Class 10 Science

Chapter 8: Heredity

Learn the fundamental mechanisms by which characteristics are passed from parents to offspring—from Mendel's famous pea plant experiments to the molecular path of gene expression and sex determination. Parents से offspring में characteristics पास होने के fundamental mechanisms को सीखें—Mendel के प्रसिद्ध pea plant experiments से लेकर gene expression और sex determination के molecular path तक।

🌐 Language / भाषा:

Remember from before:

In Class 9, we learned that cells divide using mitosis (for growth) and meiosis (to make reproductive gametes). Class 9 में, हमने सीखा था की cells growth के लिए mitosis और reproductive gametes (युग्मक) banane ke liye meiosis division का उसे करती हैं.
In Chapter 7, we saw that the creation of a chemical DNA copy is the basic event of reproduction, which leads to minor errors (variations). Chapter 7 में, हमने देखा कि chemical DNA copy बनाना reproduction का basic event है, जिससे minor errors (variations) पैदा होती हैं।
Chromosomes inside the cell nucleus hold our genetic data in DNA strands. Cell nucleus के अंदर present chromosomes (गुणसूत्र) DNA strands mein hamara genetic data hold karte hain.

1. Accumulation of Variation during Reproduction 1. Accumulation of Variation during Reproduction (जनन के दौरान विविधताओं का संचयन)

Section Goal: Explain how variations are generated during cell division and compare how they accumulate across generations in asexual vs. sexual reproduction. Section Goal: Cell division के dauran variations (विविधताएं) kaise generate hoti hain aur asexual vs. sexual reproduction mein ye generations ke sath kaise accumulate hoti hain, ise samjhein.

🖨️ The Hand-written Recipe Book Analogy 🖨️ The Hand-written Recipe Book Analogy (हाथ से लिखी रेसिपी बुक का उदाहरण)

Imagine copying a massive 100-page recipe book by hand. If you copy it alone (asexual copying), you will write very similar books, with only a rare spelling typo (variation). If you pass that slightly misspelled book to the next person to copy, they inherit your typo AND make a new typo of their own. Over time, typos pile up. However, if two people mix pages from their books (sexual copying), you get a massive variety of completely new recipes instantly! Maan लीजिए आप haath से 100 pages की ek बड़ी recipe book copy कर रहे हैं। अगर आप akele copy करते हैं (asexual copying), तो आप lagbhag same books likhenge, jisme bas कोई ek-aadhi spelling typo (variation) होगी। अगर आप वह typo वाली book किसी और को copy करने के लिए देते हैं, तो उन्हें वह typo तो milegi ही, sath ही वह अपनी nayi typo भी karenge। Dhire-dhire typos बढ़ती jayengi। लेकिन अगर do log अपने-अपने books के pages mix karke copy banate हैं (sexual copying), तो instantly nayi recipes की dheron varieties mil jayengi!

Inheritance from the previous generation provides both a common basic body design, and subtle changes in it, for the next generation [NCERT p.128]. When this new generation reproduces, the offspring will inherit the existing differences from the parents, and also develop newly created differences [NCERT p.128]. Previous generation से milne वाली inheritance से ek basic body design और usme थोड़े changes (subtle changes) next generation को मिलते हैं [NCERT p.128]। जब ये new generation reproduce करती है, तो offspring parents से मिली hui differences को inherit करते हैं और sath ही nayi variations भी develop करते हैं [NCERT p.128]।

This accumulation of differences behaves very differently depending on the type of reproduction: Differences का यह accumulation reproduction के type पर depend करता है और दोनों modes में काफी अलग होता है:

Asexual Reproduction (अलैंगिक जनन): When a single individual divides, as seen in bacteria, the resulting offspring are highly similar [NCERT p.128]. The only differences are minor, arising from tiny chemical inaccuracies during DNA replication [NCERT p.128]. If we observe a sugarcane field, we see almost zero differences among the individual plants because they are propagated asexually. Asexual Reproduction (अलैंगिक जनन): जब ek single individual divide होता है, जैसे bacteria में, तो offspring highly similar होते हैं [NCERT p.128]। Inme सिर्फ minor differences होते हैं जो DNA replication के dauran chemical inaccuracies के karan paida होते हैं [NCERT p.128]। Agar hum sugarcane (गन्ने) ka khet dekhein, toh individual plants ke beech lagbhag zero differences dikhte hain kyunki wo asexually propagate hote hain।
Sexual Reproduction (लैंगिक जनन): In organisms that reproduce sexually, like humans or dogs, two parents contribute genetic material [NCERT p.128]. This process maximizes the mixing of gene combinations, creating quite distinct, visible variations among different individuals [NCERT p.128]. Sexual Reproduction (लैंगिक जनन): Sexually reproducing organisms, जैसे humans या dogs में, do parents genetic material contribute करते हैं [NCERT p.128]। ये process gene combinations की mixing को badhata है, jisse different individuals के बीच distinct और visible variations create होती हैं [NCERT p.128]।

Environmental Selection: Environmental Selection (पर्यावरणीय चयन):

Do all these variations have an equal chance of surviving? Definitely not [NCERT p.128]. Survival depends on the nature of the variation and how it fits the environment. Kya सभी variations के survive करने के equal chances होते हैं? बिल्कुल nahi [NCERT p.128]। Survival is baat पर depend करता है की variation का nature kaisa है और वह environment के sath kaise set होता है।

🧬 Try-It Lab 1: Asexual Variation Tree Simulator 🧬 Try-It Lab 1: Asexual Variation Tree Simulator (अलैंगिक विविधता वृक्ष सिम्युलेटर)

Slide the control below to step through generations of dividing bacteria. Click on any bacterium to inspect its inherited and newly acquired mutations (variations). Dividing bacteria के generations को dekhne के लिए slider control का उसे करें। किसी भी bacterium पर click karke uske inherited और new mutations (variations) को inspect करें।

Show Generations: Show Generations (पीढ़ियाँ दिखाएं): Generation 0, 1, 2

Click a bacterium in the tree above to inspect its genetic traits and see how mutations accumulate.

⚡ Checkpoint 1

A trait X exists in 10% of a population of an asexually reproducing species and a trait Y exists in 60% of the same population. Which trait is likely to have arisen earlier? [NCERT p.129, Q1]

📝 Section Summary 📝 Section Summary (अनुभाग सारांश)

DNA Replication Errors: Inaccuracies during cell division are the fundamental cause of genetic variations. DNA Replication Errors: Cell division के दौरान होने वाली inaccuracies, genetic variations का fundamental cause हैं।
Reproduction Type: Asexual reproduction produces very little variation (clones), while sexual reproduction creates vast, distinct differences due to gene mixing. Reproduction Type: Asexual reproduction बहुत कम variation produce करता है, जबकि sexual reproduction, gene mixing के कारण बड़ी और distinct variations create करता है।
Survival Advantage: Natural selection preserves variations that help organisms withstand harsh environmental changes. Survival Advantage: Natural selection उन variations को बचाता है जो organisms को बदलते environment में survive करने में help करती हैं।

2. Rules for the Inheritance of Traits — Mendel's Contributions 2. Rules for the Inheritance of Traits — Mendel's Contributions (लक्षणों की वंशागति के नियम — मेंडेल का योगदान)

Section Goal: Learn Mendel's inheritance laws, understand dominant and recessive alleles, and analyze monohybrid and dihybrid Punnett crosses. Section Goal: Mendel के inheritance laws को seekhein, dominant और recessive alleles के बीच का difference समझें, और monohybrid/dihybrid crosses को analyze करें.

🎲 The Coin-Toss and Blueprint Mixing Analogy 🎲 The Coin-Toss and Blueprint Mixing Analogy (सिक्का उछालने और ब्लूप्रिंट मिक्सिंग का उदाहरण)

Think of your genes as a set of coins. For every trait (like height), you get one coin from your father and one from your mother. If your father gives you a 'Tall' coin (dominant) and your mother gives you a 'Short' coin (recessive), you will grow tall because the Tall coin overrides the Short one. Only if BOTH parents give you 'Short' coins will you be short. Genetic inheritance is like this probability game! अपने genes को coins के ek set की तरह समझें। हर trait (जैसे height) के लिए, आपको ek coin father से और ek mother से मिलता है। अगर father 'Tall' coin (dominant) देते हैं और mother 'Short' coin (recessive) देती हैं, तो आप tall ही grow karenge kyunki Tall coin Short वाले को override कर देता है। अगर dono parents से 'Short' coins milenge, tabhi आप short grow karenge। Genetic inheritance probability का aisa ही khel है!

The rules of inheritance in human beings are based on the fact that both parents contribute practically equal amounts of genetic material (DNA) to the child [NCERT p.129]. Thus, for each trait, every child has two versions (alleles) [NCERT p.129]. Humans में inheritance के rules is fact पर based हैं की child को dono parents से lagbhag equal amount में genetic material (DNA) मिलता है [NCERT p.129]। Iska matlab है की child में हर trait के do versions (alleles) होते हैं [NCERT p.129]।

Gregor Johann Mendel (1822–1884) worked out these basic rules using garden peas (Pisum sativum) [NCERT p.130]. He chose pea plants because they have distinct, contrasting visible characters (e.g., tall/short, round/wrinkled seeds, white/violet flowers) [NCERT p.130]. Gregor Johann Mendel (1822–1884) ne garden peas (Pisum sativum) का उसे karke basic rules of inheritance develop किए [NCERT p.130]। Unhone pea plants को isliye chuna kyunki inme distinct और contrasting characters होते हैं (जैसे tall/short, round/wrinkled seeds, white/violet flowers) [NCERT p.130]।

Figure 8.2 — Variants in human populations: (a) Free and (b) attached earlobes. Lobe attachment is a genetic trait [NCERT p.129].

1. Monohybrid Cross: Tall × Short Plants 1. Monohybrid Cross: Tall × Short Plants (एकसंकर संकरण)

Mendel crossed a pure tall plant (genotype TT) with a pure short plant (genotype tt) [NCERT p.130]: Mendel ne ek pure tall plant (genotype TT) और pure short plant (genotype tt) के बीच cross karaya [NCERT p.130]:

F1 (First Filial) Generation: All plants in the F1 progeny were tall [NCERT p.130]. There were no medium-height plants. This showed that only one parental trait—Tallness—was expressed. F1 (First Filial) Generation: F1 progeny के सभी plants tall (लंबे) the [NCERT p.130]। कोई भी medium height का plant nahi था। Isse पाता चला की parents के contrasting traits में से सिर्फ ek—tallness—ही express hua।
F2 (Second Filial) Generation: When Mendel self-pollinated the F1 tall plants (Tt × Tt), the progeny were not all tall. Instead, exactly one-quarter (25%) of them were short, and three-quarters (75%) were tall [NCERT p.130]. F2 (Second Filial) Generation: जब Mendel ne F1 tall plants (Tt × Tt) की self-pollination karayi, तो progeny के सभी plants tall nahi थे। Unme से exactly one-quarter (25%) short थे और three-quarters (75%) tall थे [NCERT p.130]।

This proved that both the tallness and shortness traits were inherited in the F1 plants, but only the tallness was visible. The trait expressed in the heterozygous state (T) is the dominant trait (प्रभावी), and the hidden trait (t) is the recessive trait (अप्रभावी) [NCERT p.130]. Isse ये prove hua की F1 plants में tallness और shortness dono traits inherit hue थे, पर सिर्फ tallness ही visible थी। Heterozygous state में जो trait express होता है (T) उसे dominant trait (प्रभावी) kehte हैं, और जो hidden रहता है (t) उसे recessive trait (अप्रभावी) kehte हैं [NCERT p.130]।

Phenotypic Ratio (बाहरी अनुपात): 3 Tall : 1 Short (3:1) [NCERT p.130] Phenotypic Ratio (बाहरी अनुपात): 3 Tall : 1 Short (3:1) [NCERT p.130]
Genotypic Ratio (जीनी अनुपात): 1 TT : 2 Tt : 1 tt (1:2:1) [NCERT p.130] Genotypic Ratio (जीनी अनुपात): 1 TT : 2 Tt : 1 tt (1:2:1) [NCERT p.130]

🌱 Try-It Lab 2: Mendel's Monohybrid Punnett Square Board 🌱 Try-It Lab 2: Mendel's Monohybrid Punnett Square Board (एकसंकर पुनेट वर्ग बोर्ड)

Build the F2 generation cross by selfing the F1 hybrid tall plant (Tt × Tt). Click on the blank cells below to toggle their genotypes, then check your answers! F1 hybrid tall plant (Tt × Tt) की selfing karake F2 generation cross बनाएं। Blank cells पर click karke genotype toggle करें, फिर answers verify करें!

F1 ♀ \ ♂

T
(Dominant)

t
(Recessive)

2. Dihybrid Cross: Independent Assortment 2. Dihybrid Cross: Independent Assortment (द्विसंकर संकरण)

Mendel also crossed plants with two differing traits: seed shape (Round/Wrinkled) and seed color (Yellow/Green) [NCERT p.131].
Crossing pure Round Yellow (RRYY) with pure Wrinkled Green (rryy) pea plants yields F1 progeny that are all Round Yellow (RrYy), establishing Round and Yellow as dominant characteristics [NCERT p.131]. Mendel ne do contrasting traits वाले plants के बीच भी crosses karaye: seed shape (Round/Wrinkled) और seed color (Yellow/Green) [NCERT p.131]।
Pure Round Yellow (RRYY) और pure Wrinkled Green (rryy) plants को cross karaye jaane पर F1 progeny के सभी seeds Round Yellow (RrYy) मिले, jisse Round और Yellow dominant traits establish hue [NCERT p.131]।

When these F1 plants self-pollinate (RrYy × RrYy), the F2 offspring exhibit entirely new combinations [NCERT p.131]: जब इन F1 plants की self-pollination (RrYy × RrYy) करायी गयी, तो F2 generation में बिल्कुल नए combinations देखने को मिले [NCERT p.131]:

Some are Round Yellow (9/16) कुछ seeds Round Yellow (9/16) थे।
Some are Round Green (3/16) — (New combination!) कुछ seeds Round Green (3/16) थे — (नया combination!)
Some are Wrinkled Yellow (3/16) — (New combination!) कुछ seeds Wrinkled Yellow (3/16) थे — (नया combination!)
Some are Wrinkled Green (1/16) कुछ seeds Wrinkled Green (1/16) थे।

This 9:3:3:1 phenotypic ratio shows that seed shape and seed color are inherited independently of each other. This is known as the Law of Independent Assortment [NCERT p.131]. यह 9:3:3:1 phenotypic ratio शो करता है कि seed shape और seed color एक दूसरे से independently inherit होते हैं। इस नियम को Law of Independent Assortment (स्वतंत्र अपव्यूहन का नियम) कहते हैं [NCERT p.131]।

🟢 Try-It Lab 3: Dihybrid Cross Interactive Sandbox (16-Cell Grid) 🟢 Try-It Lab 3: Dihybrid Cross Interactive Sandbox (द्विसंकर संकरण सैंडबॉक्स)

Click on the buttons below to highlight specific seed phenotypes in the 4x4 F2 cross. Notice how the traits assort independently to yield the 9:3:3:1 ratio! You can also click individual cells to inspect their specific genotype. 4x4 F2 cross में specific phenotypes को highlight करने के लिए नीचे दिए buttons पर click करें। Dekhein kaise traits independently segregate hokar 9:3:3:1 ratio banate हैं! हर cell पर click karke genotype inspect किया ja सकता है।

RY\RY

RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

Click a seed in the Punnett square or filter above to inspect its genetic data.

⚡ Checkpoint 2

What does a 9:3:3:1 phenotypic ratio in an F2 generation represent?

📝 Section Summary 📝 Section Summary (अनुभाग सारांश)

Contrasting Characters: Mendel's pea plant crossings established dominant (expressed in Tt) and recessive (expressed only in tt) traits. Contrasting Characters: Mendel ने pea plant crossings से establish किया कि traits, dominant (जो Tt में express होता है) और recessive (जो सिर्फ tt में express होता है) होते हैं।
Monohybrid Cross (TT × tt): Yields an F1 generation that is 100% tall, and an F2 generation with a 3:1 phenotypic (Tall:Short) and a 1:2:1 genotypic ratio. Monohybrid Cross (TT × tt): इससे F1 generation 100% tall मिलती है, और F2 generation में 3:1 phenotypic (Tall:Short) और 1:2:1 genotypic ratio मिलता है।
Dihybrid Cross (RRYY × rryy): F2 generation self-cross yields a 9:3:3:1 phenotypic ratio, proving independent assortment. Dihybrid Cross (RRYY × rryy): F2 generation के self-cross से 9:3:3:1 ratio मिलता है, जो independent assortment को prove करता है।

3. How do these Traits get Expressed? 3. How do these Traits get Expressed? (लक्षण अपने आप को कैसे व्यक्त करते हैं?)

Section Goal: Trace the chemical path of inheritance from a DNA segment (gene) to an active protein/enzyme that dictates physical trait development. Section Goal: DNA segment (gene) से lekar active protein/enzyme तक के chemical path of inheritance को समझें जो body traits के expression को direct करते हैं.

🏭 The Factory Machine Manual Analogy 🏭 The Factory Machine Manual Analogy (फैक्ट्री मशीन मैनुअल का उदाहरण)

How does cellular inheritance actually control physical characteristics? Cellular inheritance actual physical characteristics को kaise control करती है?

How does cellular inheritance actually control physical characteristics?

The DNA Blueprint: Cellular DNA is the ultimate source of information for synthesizing proteins in the cell [NCERT p.131]. The DNA Blueprint: Cellular DNA cell के अंदर proteins की synthesis के लिए primary information source है [NCERT p.131]।
The Gene: A section of DNA that provides instructions for making one specific protein is called the gene (जीन) for that protein [NCERT p.131]. The Gene: DNA का वह section जो ek specific protein banane के लिए information देता है, उसे us protein का gene (जीन) kehte hain [NCERT p.131]।
Protein & Enzymes: Genes control traits by producing proteins. Many of these proteins are enzymes [NCERT p.131]. Let's take plant height as an example. Plant growth is triggered by hormones. The amount of hormone made depends directly on the efficiency of the enzyme responsible for making it [NCERT p.131]. Protein & Enzymes: Genes proteins banakar traits को control करते हैं। Inme से kayi proteins enzymes होते हैं [NCERT p.131]। Example के लिए plant height को lete हैं। Plant height growth hormone पर depend करती है, और hormone kitna banega ये उसे banane वाले enzyme की efficiency पर depend करता है [NCERT p.131]।
Trait Expression: If the gene provides instructions for a highly efficient enzyme, a lot of plant hormone is made, and the plant will grow tall [NCERT p.131]. If the gene has an alteration (mutation) that makes the enzyme less efficient, less hormone is synthesized, and the plant remains short [NCERT p.131]. Trait Expression: अगर gene ek efficient enzyme banane की instruction देता है, तो dher सारा plant hormone banega और plant tall grow karega [NCERT p.131]। लेकिन अगर gene में कोई change (mutation) हो jisse enzyme less efficient हो jaye, तो hormone कम banega और plant short reh jayega [NCERT p.131]।

Key concept: Chromosomes as Independent Pieces
During sexual reproduction, each parent contributes a copy of the same gene, meaning every cell has two sets of all genes, housed on homologous pairs of chromosomes [NCERT p.131]. Germ cells (gametes) receive only one chromosome from each homologous pair [NCERT p.132]. When a maternal and paternal gamete fuse at fertilization, the normal double set of chromosomes is fully restored, ensuring genetic stability across species [NCERT p.132]. Key concept: Chromosomes as Independent Pieces
Sexual reproduction के dauran, dono parents same gene की ek-ek copy contribute करते हैं, jisse cell में हर gene के do sets ban जाते हैं, जो chromosomes के homologous pairs पर होते हैं [NCERT p.131]। Germ cells (gametes) को इन homologous pairs में से ek ही chromosome मिलता है [NCERT p.132]। जब maternal और paternal gametes fertilization के समय fuse होते हैं, तो chromosomes का normal double set फिर से restore हो jata है, jisse species की genetic stability बनी रहती है [NCERT p.132]।

⚙️ Try-It Lab 4: Gene-to-Protein Trait Pathway Simulator ⚙️ Try-It Lab 4: Gene-to-Protein Trait Pathway Simulator (जीन-टू-प्रोटीन लक्षण मार्ग सिम्युलेटर)

Adjust the slider to change the enzyme efficiency level. Watch the molecular path from DNA transcription down to the physical height of the pea plant! Enzyme efficiency level को change करने के लिए slider को adjust करें। DNA transcription से lekar pea plant की height तक के pure molecular pathway को dekhein!

Enzyme Efficiency: Enzyme Efficiency (एन्जाइम दक्षता): 100% (High)

Normal Gene: The gene provides standard instructions, creating a highly efficient enzyme. This synthesizes abundant growth hormone, leading to cell elongation and a TALL plant.

⚡ Checkpoint 3

What determines whether a pea plant grows tall or remains short at a biochemical level?

📝 Section Summary 📝 Section Summary (अनुभाग सारांश)

Gene to Trait Path: Genes serve as templates to build proteins (enzymes) that catalyze hormone synthesis, regulating physical characteristics. Gene to Trait Path: Genes templates की तरह काम करते हैं जो hormone synthesis को catalyze करने वाले proteins (enzymes) बनाते हैं, और body traits को regulate करते हैं।
Homologous Pairs: Organisms inherit two sets of chromosomes, providing two alleles for every genetic trait. Homologous Pairs: Organisms, chromosomes के दो sets inherit करते हैं, जिससे हर genetic trait के लिए दो alleles मिलते हैं।
Gamete Fusion: Germ cells are haploid (one set of chromosomes), and their fusion at fertilization restores the diploid number (two sets). Gamete Fusion: Germ cells haploid (chromosomes का single set) होते हैं, और fertilization के समय इनका fusion, chromosome number को restore करके diploid (double set) कर देता है।

4. Sex Determination 4. Sex Determination (लिंग निर्धारण)

Section Goal: Explain how sex is determined in different organisms and describe the genetic, chromosomal mechanisms in humans. Section Goal: Alag-alag organisms में biological sex kaise determine किया jata है, और humans में iske chromosomal mechanism को समझें.

🪙 The Coin Flip Analogy 🪙 The Coin Flip Analogy (सिक्का उछालने का उदाहरण)

Different species use very different strategies to decide the sex of a newborn child [NCERT p.132]: Alag-alag species newborn baby का sex determine करने के लिए different strategies उसे करती हैं [NCERT p.132]:

Different species use very different strategies to decide the sex of a newborn child [NCERT p.132]:

Environmental Sex Determination: Some reptiles depend completely on temperature. The temperature at which fertilized eggs are incubated determines whether the developing embryo becomes male or female [NCERT p.132]. Snails can even change their sex during their lifetime, proving their sex is not genetically fixed [NCERT p.132]. Environmental Sex Determination: कुछ reptiles poori तरह temperature पर depend करते हैं। Egg incubation के temperature से determine होता है की embryo male banega या female [NCERT p.132]। Snails अपना sex भी badal सकते हैं, जो show करता है की उनका sex genetically fixed nahi होता [NCERT p.132]।
Genetic Sex Determination: In human beings, sex is determined genetically. The genes inherited from our parents decide the biological sex from the moment of fertilization [NCERT p.132]. Genetic Sex Determination: Humans में sex genetically determine होता है। Parents से inherit hone वाले genes fertilization के time ही biological sex fix कर देते हैं [NCERT p.132]।

Sex Chromosomes in Humans: Sex Chromosomes in Humans (मानवों में लिंग गुणसूत्र):

Human cells contain 23 pairs of chromosomes [NCERT p.132]: Human cells में chromosomes के 23 pairs होते हैं [NCERT p.132]:

Autosomes (अलिंग गुणसूत्र): 22 pairs are perfect matching pairs, identical in both men and women, carrying body features [NCERT p.132]. Autosomes (अलिंग गुणसूत्र): 22 pairs perfect matching pairs होते हैं, जो men और women dono में same होते हैं और physical features carry करते हैं [NCERT p.132]।
Sex Chromosomes (लिंग गुणसूत्र): 1 pair determines sex [NCERT p.132]. Sex Chromosomes (लिंग गुणसूत्र): 1 pair biological sex determine करता है [NCERT p.132]।

Since mothers are XX, all their eggs carry an X chromosome [NCERT p.132]. Since fathers are XY, half of their sperm carry an X chromosome, and the other half carry a Y chromosome [NCERT p.132]. Mother XX होती हैं, isliye उनके सभी eggs में ek X chromosome होता है [NCERT p.132]। Father XY होते हैं, isliye उनके aadh (50%) sperm में X chromosome और aadh (50%) में Y chromosome होता है [NCERT p.132]।

If an X-carrying sperm fertilizes the egg, the zygote is XX (Girl) [NCERT p.132]. अगर ek X-carrying sperm egg को fertilize करता है, तो zygote XX (Girl) बनता है [NCERT p.132]।
If a Y-carrying sperm fertilizes the egg, the zygote is XY (Boy) [NCERT p.132]. अगर ek Y-carrying sperm egg को fertilize करता है, तो zygote XY (Boy) बनता है [NCERT p.132]।

Thus, the sex of a child is determined entirely by what chromosome they inherit from their father [NCERT p.132]. The mother's genetic contribution is always X. Is तरह child का biological sex poori तरह is baat पर depend करता है की उसे father से kaunsa chromosome मिलता है [NCERT p.132]। Mother का genetic contribution हमेशा X ही होता है।

👶 Try-It Lab 5: Sex Determination & Fertilization Lab 👶 Try-It Lab 5: Sex Determination & Fertilization Lab (लिंग निर्धारण और निषेचन लैब)

Select which sperm cell fertilizes the mother's egg cell to see zygote formation, or simulate 100 births to test the statistical ratio! Zygote formation देखने के लिए select करें कि कौनसा sperm, egg cell को fertilize करेगा, या 100 births simulate करके statistical ratio test करें!

Mother (XX) Mother (XX / माता)

Father (XY) Father (XY / पिता)

Girls (XX) Count: 0 Boys (XY) Count: 0

Click one of the "Send Sperm" buttons to initiate fertilization and view genetic results.

⚡ Checkpoint 4

What is the mathematical probability of a child being born a boy in a human pregnancy?

📝 Section Summary 📝 Section Summary (अनुभाग सारांश)

Varying Sex Strategies: Reptile sex is often determined by egg incubation temperature, snails can change sex, and humans determine sex genetically. Varying Sex Strategies: Reptiles में sex temperature पर depend करता है, snails अपना sex change कर सकते हैं, और humans में sex genetic होता है।
Odd Chromosome Pair: Human females possess XX sex chromosomes, while males have mismatched XY chromosomes. Odd Chromosome Pair: Human females के पास XX sex chromosomes होते हैं, जबकि males के पास mismatched XY chromosomes होते हैं।
Paternal Origin: The father's sperm carries either X or Y, determining the biological sex of the offspring. Paternal Origin: Father का sperm या तो X या Y carry करता है, जो offspring का biological sex determine करता है।

NCERT Solutions NCERT Solutions (पाठ्यपुस्तक के हल)

In-Text Questions (Textbook Page 129)

Q1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier? Q1. अगर asexually reproducing species की population में trait A 10% individuals में और trait B 60% individuals में present है, तो कौनसा trait पहले पैदा हुआ होगा?

Answer: Trait B is likely to have arisen earlier.
Explanation: In asexual reproduction, genetic information is copied from a single parent with very high fidelity, producing offspring that are almost identical. Any variation arises only from rare errors in DNA replication. Once a variation appears, it is inherited by all subsequent generations. Since Trait B is found in 60% of the population, it must have been replicated and passed down for a much longer period. Trait A (10%) is present in a much smaller fraction, suggesting it is a newer mutation that has only recently arisen. Answer: Trait B पहले paida hua होगा।
Explanation: Asexual reproduction में genetic information single parent से copy होती है, jisse offspring almost identical होते हैं। कोई भी variation DNA replication में errors के karan ही आती है। Ek बार variation आने के बाद वह आगे के generations में copy होती रहती है। Chunki Trait B 60% population में है, iska matlab है की ये kaafi पहले से reproduce और pass हो रहा है। Trait A सिर्फ 10% में है, जो show करता है की ये ek naya mutation है जो haal ही में paida hua है।

Q2. How does the creation of variations in a species promote survival? Q2. किसी species में variations पैदा होने से उसका survival कैसे बढ़ता है?

Answer: Variations promote species survival by serving as a genetic safety net against sudden environmental changes.
Explanation: Ecosystem niches can shift drastically due to temperature spikes, droughts, floods, or diseases. If all members of a species are identical (no variation) and a severe environmental change occurs, the entire population could be wiped out. However, if a population has genetic variation, a few individuals might possess traits (like heat resistance or disease immunity) that allow them to survive the change. These survivors will reproduce and multiply, ensuring the survival of the species. Answer: Variations badlte environment के khilaf ek genetic safety net banakar species के survival को ensure करती हैं।
Explanation: Temperature shifts, drought, flood, या disease के karan ecosystem niches badal सकते हैं। अगर species के सारे individuals identical honge (no variation) और कोई badlaav आता है, तो poori population khatam हो सकती है। लेकिन अगर population में genetic variations हैं, तो कुछ individuals में aisi qualities हो सकती हैं (जैसे heat resistance या immunity) जो उन्हें survive करने में help करें। ये survivors multiply karenge, jisse species का survival बचा rahega।

In-Text Questions (Textbook Page 133)

Q1. How do Mendel’s experiments show that traits may be dominant or recessive? Q1. Mendel के experiments से कैसे पता चलता है कि traits, dominant या recessive हो सकते हैं?

Answer: Mendel proved this by crossing tall (TT) and short (tt) pea plants:

In the first generation (F1), all progeny were tall plants. No short or medium plants were produced. This showed that out of the two contrasting traits, only one—tallness—was expressed.
When Mendel self-pollinated these F1 tall plants (Tt), the short trait reappeared in the F2 generation, making up 25% of the offspring.

This proved that F1 plants carried the gene for shortness but did not express it. The trait that expresses itself in the presence of a contrasting allele is the dominant trait (Tallness 'T'), and the trait that remains hidden is the recessive trait (Shortness 't'). Answer: Mendel ne pure tall (TT) और pure short (tt) pea plants के बीच cross karake ये prove किया:

First generation (F1) में सभी plants tall थे, कोई भी short या medium height का nahi था। Isse पाता चला की do contrasting traits में से सिर्फ ek (tallness) ही express hua।
जब Mendel ne F1 tall plants (Tt) की self-pollination karayi, तो F2 generation में short trait wapas aa गया, जो total offspring का 25% था।

Isse prove hua की F1 plants short gene carry कर रहे थे पर express nahi कर paa रहे थे। Heterozygous state में जो trait express होता है उसे dominant trait (Tallness 'T') और जो chupa रहता है उसे recessive trait (Shortness 't') kehte हैं।

Q2. How do Mendel’s experiments show that traits are inherited independently? Q2. Mendel के experiments से कैसे पता चलता है कि traits independently inherit होते हैं?

Answer: Mendel crossed plants differing in two traits: seed shape (Round/Wrinkled) and color (Yellow/Green).
Crossing pure Round Yellow (RRYY) with Wrinkled Green (rryy) yielded all Round Yellow (RrYy) F1 plants.
When F1 plants self-pollinated to produce the F2 generation, they yielded four distinct types:

Round Yellow (9) — Parental combination
Wrinkled Green (1) — Parental combination
Round Green (3) — New combination
Wrinkled Yellow (3) — New combination

The emergence of these new, non-parental combinations (Round Green and Wrinkled Yellow) in a 9:3:3:1 ratio proves that seed shape and seed color are not linked. They segregate and are inherited independently of one another. Answer: Mendel ne do contrasting traits वाले plants के बीच cross karaya: seed shape (Round/Wrinkled) और seed color (Yellow/Green)।
Pure Round Yellow (RRYY) और Wrinkled Green (rryy) के cross से F1 generation के सभी plants Round Yellow (RrYy) मिले।
जब F1 plants की self-pollination से F2 generation produce hui, तो chaar types के combinations मिले:

Round Yellow (9) — Parental combination
Wrinkled Green (1) — Parental combination
Round Green (3) — Naya combination
Wrinkled Yellow (3) — Naya combination

9:3:3:1 ratio में naye combinations (Round Green और Wrinkled Yellow) का milna prove करता है की seed shape और color linked nahi हैं। ये independent segregation दिखाते हैं और separate inherit होते हैं।

Q3. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not? Q3. Blood group A वाले ek man ne blood group O वाली woman से marriage की और उनकी daughter का blood group O है। Kya ये information ये batane के लिए kafi है की blood group A और O में से kaunsa dominant है? क्यों या क्यों nahi?

Answer: No, this information is not enough to determine which blood group is dominant.
Explanation: Blood group alleles in humans can be heterozygous or homozygous.

Case 1: If blood group A is dominant and blood group O is recessive: The man must be heterozygous A (I^AI^O) and the woman must be homozygous O (I^OI^O). The daughter inherits I^O from the mother and I^O from the father, resulting in blood group O (I^OI^O). This is fully consistent.
Case 2: If blood group O is dominant and blood group A is recessive: The woman is homozygous O (I^OI^O) and the man is homozygous A (I^AI^A). Under this case, the daughter would inherit O and be O, but the man's A would have to behave differently. However, even if the father is heterozygous A, we cannot rule out dominance.

Since both inheritance models can explain a daughter having blood group O depending on the parents' zygosity, we need more data (such as the blood groups of the father's parents or crossing patterns of other children) to conclude which trait is dominant. (In genetics, I^A is dominant and I^O is recessive). Answer: Nahi, ये information dominant blood group batane के लिए kafi nahi (not enough) है।
Explanation: Humans में blood group alleles heterozygous या homozygous हो सकते हैं:

Case 1: Agar blood group A dominant hai और blood group O recessive है: तो man heterozygous A (I^AI^O) और woman homozygous O (I^OI^O) हो सकते हैं। Daughter को mother से I^O और father से I^O milega, jisse uska group O (I^OI^O) होगा। ये possible है।
Case 2: Agar blood group O dominant hai और blood group A recessive है: तो woman homozygous O (I^OI^O) और man heterozygous A (I^AI^O) या homozygous recessive A हो सकते हैं। Yahan भी daughter का O hona possible है।

Chunki parents के genetic structures के basis पर dono chances possible हैं, हम सिर्फ is single case से design predict nahi कर सकते। Hamein man के parents या उनके baki bachon के blood groups की mazeed information चाहिए होगी। (Genetics के rules के according I^A dominant और I^O recessive होता है)।

Q4. How is the sex of the child determined in human beings? Q4. Humans में child का sex कैसे determine किया जाता है?

Answer: In humans, sex is determined genetically by the 23rd chromosome pair (sex chromosomes) contributed by the parents:

Females have two identical sex chromosomes: XX. All eggs carry an X chromosome.
Males have mismatched sex chromosomes: XY. Half of the sperm carry an X, and the other half carry a Y.

During fertilization, the sex of the child depends on the fertilizing sperm:

If an X-carrying sperm fertilizes the egg, the zygote is XX → Girl.
If a Y-carrying sperm fertilizes the egg, the zygote is XY → Boy.

Therefore, the father's sperm determines the sex of the child. The probability is exactly 50% for each sex. Answer: Humans में sex genetic factors द्वारा, parents से milne वाले 23rd chromosome pair (sex chromosomes) से decide होता है:

Females के पास matching sex chromosomes XX होते हैं। Isliye सभी eggs में ek X chromosome होता है।
Males के पास mismatched pair XY होता है। Isliye aadh sperms X और aadh Y carry करते हैं।

Fertilization के time, child का sex fertilizing sperm के nature पर depend करता है:

अगर egg को X-carrying sperm fertilize kare, तो zygote XX (Ladki) बनता है।
अगर egg को Y-carrying sperm fertilize kare, तो zygote XY (Ladka) बनता है।

Isliye baby का sex decide करने में father के sperm का role होता है। Iske probability exactly 50% (1:1) होती है।

Chapter-End Exercises (Textbook Page 133)

Q1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as:
(a) TTWW (b) TTww (c) TtWW (d) TtWw Q1. Ek Mendelian experiment में violet flowers वाले tall pea plants को white flowers वाले short pea plants से cross karaya गया। F1 progeny के सभी flowers violet setting के थे, पर unme से lagbhag aadh plants short height के थे। Isse पाता चला की tall parent का genetic makeup kaisa था?
(a) TTWW (b) TTww (c) TtWW (d) TtWw

Correct Answer: (c) TtWW
Explanation: Let's analyze the traits one by one:

Flower Color: Since all progeny bore violet flowers (none were white), the tall parent must be homozygous dominant for violet color (WW), which completely masks the recessive white color (w).
Plant Height: Since almost half (50%) of the progeny were short, the tall parent must be heterozygous for height (Tt). Crossing Tt (heterozygous tall) with tt (short) yields 50% Tt (tall) and 50% tt (short) offspring. If the parent were TT (homozygous tall), 100% of the offspring would be tall.

Combining these gives the genotype TtWW. Correct Answer: (c) TtWW
Explanation: चलें traits को alag-alag check करते हैं:

Flower Color: Progeny के सभी flowers violet थे (कोई white nahi था), iska matlab है की tall parent violet color के लिए homozygous dominant (WW) था, जो recessive white (w) को suppress कर देता है।
Plant Height: Lagbhag 50% progeny short थी, iska matlab है की tall parent height के लिए heterozygous (Tt) था। Tt और tt के cross से ही 50% short offspring मिलते हैं। अगर parent TT (homozygous tall) होता, तो सभी offspring tall होते।

Dono को combine करने पर genotype TtWW बनता है।

Q2. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not? Q2. Ek study में देखा गया की light eye color वाले bachon के parents की eyes भी light color की थी। Kya is information पर हम bol सकते हैं की light eye color dominant trait है या recessive? क्यों या क्यों nahi?

Answer: On this basis alone, we cannot conclude whether light eye color is dominant or recessive.
Explanation:

If light eye color were a recessive trait (say, 'e'), then parents with light eyes must be homozygous recessive (ee). Two light-eyed parents (ee × ee) can only produce light-eyed children (100% ee). This matches the study's observation.
If light eye color were a dominant trait (say, 'E'), then parents could be homozygous (EE) or heterozygous (Ee). If parents are EE × EE or EE × Ee, their children will all have light eyes. Even if both parents are Ee × Ee, 75% of their children will have light eyes.

Because both scenarios can explain the outcome, the data is insufficient. We need to analyze pedigree charts over multiple generations or cross light-eyed individuals with dark-eyed individuals to see which trait is masked in the F1 generation. Answer: सिर्फ is information के basis पर हम conclude nahi kar sakte की light eye color dominant है या recessive।
Explanation:

अगर light eye color ek recessive trait (say, 'e') है: तो dono light-eyed parents homozygous recessive (ee) honge। Do ee × ee parents के सारे bache light eyes (ee) वाले ही honge। ये observation से match करता है।
अगर light eye color ek dominant trait (say, 'E') है: तो parents homozygous (EE) या heterozygous (Ee) हो सकते हैं। अगर parents EE × EE या EE × Ee हैं, तो भी bachon की eyes light hongi।

Chunki dono तरह के traits (dominant/recessive) से ये outcome हो सकता है, ये data insufficient है। Hamein multiple generations की pedigree history check karni होगी या light eyes को dark eyes के sath cross karana होगा।

Q3. Outline a project which aims to find the dominant coat colour in dogs. Q3. Dogs में dominant coat color (twacha का रंग) find करने के लिए ek project design kijiye।

Answer: Here is a project design to determine the dominant coat color in dogs (e.g., Black vs. White):

Selection of Parents: Select a purebred black male dog (homozygous) and a purebred white female dog (homozygous). Ensure they belong to the same breed to control other genetic variables.
F1 Generation: Breed the two dogs. Observe the coat color of all puppies in the resulting litter (F1 generation).
- If all F1 puppies have a black coat, then Black is dominant and White is recessive.
- If all F1 puppies have a white coat, then White is dominant and Black is recessive.
F2 Generation Confirmation: Breed the F1 sibling dogs (or cross an F1 dog with another heterozygous dog of the same generation). Observe the coat colors of the F2 litter. If the recessive coat color reappears in approximately a 3:1 phenotypic ratio (3 dominant : 1 recessive), the dominance is confirmed.

Answer: Dogs में dominant coat color (जैसे Black vs White) पाता करने के लिए project design:

Selection of Parents: Ek purebred homozygous black male और ek homozygous white female chunein। Dhyaan रहे की dono same breed के hon taaki traits control हो sakein।
F1 Generation: Dono dogs की breeding karayein। Puppies के coat color (twacha का रंग) को observe करें:
- अगर सभी puppies black हैं, तो Black dominant है और White recessive.
- अगर सभी puppies white हैं, तो White dominant है और Black recessive.
F2 Generation Confirmation: F1 puppies के बीच breeding karayein। F2 offspring के colors check करें। अगर approximately 3:1 ratio (3 dominant : 1 recessive) में colors आते हैं, तो dominance check completely verify हो jati है।

Q4. How is the equal genetic contribution of male and female parents ensured in the progeny? Q4. Progeny में male और female parents का equal genetic contribution कैसे ensure किया जाता है?

Answer: Equal genetic contribution is ensured through cell division by meiosis and fertilisation:

Diploid Body Cells (2n): Normal human body cells are diploid, meaning they contain 46 chromosomes arranged in 23 homologous pairs (one set from the father, one from the mother).
Haploid Gametes (n) via Meiosis: During gamete formation, special reproductive cells undergo meiosis (reduction division). This halves the chromosome number, producing sperm and egg cells that have only 23 single chromosomes (haploid, n). Each gamete gets exactly one chromosome from each homologous pair.
Restoration during Fertilisation (2n): When a haploid sperm (23 chromosomes) fuses with a haploid egg (23 chromosomes), they form a diploid zygote with 46 chromosomes (23 pairs).

This zygote has one maternal and one paternal copy of each chromosome, ensuring that both parents contribute exactly 50% of the genetic material to the child. Answer: Offspring में biological parents का genetic material barabar (equal) meiosis और fertilization process के through ensure किया jata है:

Diploid Cells (2n): Normal human cells में chromosomes के 23 pairs (total 46 chromosomes) होते हैं, jisme ek set mother से और ek father से आता है।
Haploid Gametes (n): Gamete formation के time special cell division meiosis (अर्धसूत्री विभाजन) hota hai। Isse chromosome number aadha hokar 23 reh jata hai (sperm aur egg cell mein)।
Fertilisation (2n): जब haploid sperm (23 chromosomes) और haploid egg (23 chromosomes) fuse होते हैं, तो diploid zygote (46 chromosomes, 23 pairs) बनता है।

Is तरह child में 50% DNA father से और 50% DNA mother से inherit होता है, jisse equal genetic contribution ensure हो jata है।

Solved CBSE Board PYQs Solved CBSE Board PYQs (हल किए गए बोर्ड प्रश्न)

1 Mark Questions (Very Short Answer) 1 Mark Questions (Very Short Answer / अति लघु उत्तरीय)

Q1. Define heredity. [CBSE 2020] Q1. Heredity (आनुवंशिकता) ko define karein। [CBSE 2020]

Answer: Heredity is the transmission of genetic characters and traits from parents to their offspring through generations. Answer: Parents से offspring में genetic characters और traits के generations-wise transfer hone की process को heredity (आनुवंशिकता) kehte hain।

Q2. Write the scientific name of the plant Mendel chose for his hybridization experiments. [CBSE 2018] Q2. Mendel द्वारा उसे किए गए garden plant का scientific name लिखें। [CBSE 2018]

Answer: Pisum sativum (commonly known as the garden pea plant). Answer: Pisum sativum (Garden pea plant ya मटर का पौधा)।

2 Marks Questions (Short Answer I) 2 Marks Questions (Short Answer I / लघु उत्तरीय I)

Q3. State two reasons why Mendel chose pea plants for his inheritance experiments. [CBSE 2019] Q3. Mendel द्वारा pea plants select करने के do main reasons बताएं। [CBSE 2019]

Answer: Mendel selected the garden pea plant (Pisum sativum) for the following reasons:

Distinct contrasting characters: Pea plants have clear, easy-to-see contrasting traits (such as Tall/Short plants, Round/Wrinkled seeds, Yellow/Green seeds) making observation simple.
Short life cycle & self-pollination: Pea plants have a short life cycle (generating results quickly) and are naturally self-pollinating, making it easy to create pure lines, but can also be easily cross-pollinated manually.

Answer: Mendel ne garden pea plant (Pisum sativum) को इन reasons के लिए chuna:

Distinct contrasting characters: Inme clear और contrasting physical features होते हैं (जैसे Tall/Short, Round/Wrinkled, Yellow/Green) jisse calculation asaan हो गयी।
Short life cycle & self-pollination: Inka life cycle छोटा होता है (fast results के लिए) और ये naturally self-pollinating होते हैं, jisse pure lines create करना easy हो jata है।

Q4. Distinguish between genotype and phenotype. [CBSE 2023] Q4. Genotype और phenotype के बीच distinction (difference) clear करें। [CBSE 2023]

Answer: The differences are:

Feature	Genotype (जीनोटाइप)	Phenotype (फेनोटाइप)
Definition	It is the genetic constitution or gene makeup of an organism for a specific trait.	It is the observable physical appearance or visible characteristics of an organism.
Example	Genotypes for height: TT (homozygous tall) or Tt (heterozygous tall).	Phenotype for height: Tall plant.

Answer: Dono के बीच differences नीचे दिए गए हैं:

Feature	Genotype (जीनोटाइप)	Phenotype (फेनोटाइप)
Definition	ये किसी trait के लिए organism का actual gene configuration (genetic constitution) होता है।	Ye organism ke physical features ka observable, visible appearance (बाहरी रूप) hota hai।
Example	Height के लिए genotype: TT (homozygous tall) या Tt (heterozygous tall)।	Height ke liye phenotype: Tall (लंबा) plant।

3 Marks Questions (Short Answer II) 3 Marks Questions (Short Answer II / लघु उत्तरीय II)

Q5. In a monohybrid cross between tall pea plants (TT) and short pea plants (tt), Mendel obtained only tall plants in the F1 generation. However, in the F2 generation, short plants reappeared. Explain this finding with a cross diagram. [CBSE 2022] Q5. Tall (TT) और short (tt) plants के monohybrid cross में F1 generation में सिर्फ tall plants मिले, पर F2 generation में short plants reappeared हो गए। Ise cross diagram के sath समझें। [CBSE 2022]

Answer:
When Mendel crossed pure Tall (TT) with pure Short (tt) plants:
1. F1 Generation: All offspring inherit 'T' from the tall parent and 't' from the short parent, forming heterozygous Tt. Since 'T' (tallness) is dominant, it completely masks the recessive allele 't'. Hence, all F1 plants appear tall.
2. F2 Generation: Selfing F1 (Tt × Tt) allows segregation of alleles during gamete formation. Gametes can carry either T or t.
Crossing these gametes gives:

TT (Homozygous Tall) — 25%
Tt (Heterozygous Tall) — 50%
tt (Homozygous Short) — 25%

Since 'tt' has no dominant 'T' allele, the shortness trait is expressed, and short plants reappear in a 3 Tall : 1 Short ratio. Answer:
जब Mendel ne pure Tall (TT) और pure Short (tt) plants को cross karaya:
1. F1 Generation: सभी offspring Tall parent से 'T' और Short parent से 't' inherit करते हैं, jisse heterozygous Tt बनता है। dominant allele 'T' recessive allele 't' के impact को suppress कर देता है, isliye सभी F1 plants tall दिखते हैं।
2. F2 Generation: F1 plants (Tt × Tt) की selfing से gametes form होते हैं जो या तो T या t carry करते हैं।
Gamete crossings से:

TT (Homozygous Tall) — 25%
Tt (Heterozygous Tall) — 50%
tt (Homozygous Short) — 25%

Chunki 'tt' zygote में dominant 'T' nahi है, short height trait express हो jata है और short plants 3 Tall : 1 Short ratio में wapas aa जाते हैं।

5 Marks Questions (Long Answer) 5 Marks Questions (Long Answer / दीर्घ उत्तरीय)

Q6. (a) What is a dihybrid cross? Explain with the help of a Punnett square Mendel's cross of Round Yellow and Wrinkled Green seeds.
(b) State the law formulated from these results. [CBSE 2020] Q6. (a) Dihybrid cross kya होता है? Round Yellow और Wrinkled Green seeds के cross को Punnett square के sath explain करें।
(b) Is experiment से जो rule develop hua उसे state करें। [CBSE 2020]

Answer:
(a) Dihybrid Cross: A cross made between two plants differing in two pairs of contrasting traits (such as seed shape and seed color).
Mendel crossed pure Round Yellow (RRYY) seeds with Wrinkled Green (rryy) seeds:

Parental Gametes: RY from RRYY parent and ry from rryy parent.
F1 Progeny: All offspring are heterozygous RrYy, producing Round Yellow seeds (since Round 'R' and Yellow 'Y' are dominant).
Selfing F1 (RrYy × RrYy): F1 plants produce four types of gametes in equal proportions: RY, Ry, rY, ry.

The F2 Punnett square is:

Gametes	RY	Ry	rY	ry
RY	RRYY (Round Yellow)	RRYy (Round Yellow)	RrYY (Round Yellow)	RrYy (Round Yellow)
Ry	RRYy (Round Yellow)	RRyy (Round Green)	RrYy (Round Yellow)	Rryy (Round Green)
rY	RrYY (Round Yellow)	RrYy (Round Yellow)	rrYY (Wrinkled Yellow)	rrYy (Wrinkled Yellow)
ry	RrYy (Round Yellow)	Rryy (Round Green)	rrYy (Wrinkled Yellow)	rryy (Wrinkled Green)

This yields 4 distinct phenotypes in F2:

Round Yellow: 9
Round Green: 3
Wrinkled Yellow: 3
Wrinkled Green: 1

Phenotypic Ratio is 9:3:3:1.

(b) Law of Independent Assortment: Based on these results, Mendel formulated the Law of Independent Assortment. It states that when two pairs of contrasting traits are combined in a hybrid cross, the segregation and inheritance of one pair of characters is completely independent of the inheritance of the other pair. Answer:
(a) Dihybrid Cross (द्विसंकर संकरण): Do pairs of contrasting features (contrasting traits) वाले different plants के बीच karaya गया cross (जैसे seed shape और seed color)।
Mendel ne pure Round Yellow (RRYY) और pure Wrinkled Green (rryy) seeds को cross karaya:

Parental Gametes: RRYY parent से RY और rryy parent से ry gametes आते हैं।
F1 Progeny: सभी offspring heterozygous RrYy (Round Yellow) होते हैं (Round 'R' और Yellow 'Y' dominant hone के karan)।
Selfing F1 (RrYy × RrYy): F1 plants 4 type के gametes banate हैं: RY, Ry, rY, ry।

F2 generation का Punnett square नीचे table में देख सकते हैं:

Gametes	RY	Ry	rY	ry
RY	RRYY (Round Yellow)	RRYy (Round Yellow)	RrYY (Round Yellow)	RrYy (Round Yellow)
Ry	RRYy (Round Yellow)	RRyy (Round Green)	RrYy (Round Yellow)	Rryy (Round Green)
rY	RrYY (Round Yellow)	RrYy (Round Yellow)	rrYY (Wrinkled Yellow)	rrYy (Wrinkled Yellow)
ry	RrYy (Round Yellow)	Rryy (Round Green)	rrYy (Wrinkled Yellow)	rryy (Wrinkled Green)

Isse 4 phenotypes मिलते हैं:

Round Yellow: 9
Round Green: 3
Wrinkled Yellow: 3
Wrinkled Green: 1

F2 Phenotypic ratio 9:3:3:1 होता है।

(b) Law of Independent Assortment (स्वतंत्र अपव्यूहन का नियम): Is experiment के basis पर Mendel ne independent assortment का rule दिया। Is rule के according, जब do contrasting features वाले hybrid cross होते हैं, तो characters के segregate और inherit hone की process ek-dusre से completely independent होती है, yaani seed shape और seed color के transmission पर आपस में कोई dependency nahi होती।

☑ What You Can Now Do: ☑ What You Can Now Do (अब आप यह कर सकते हैं):

Explain why sexual reproduction creates far greater genetic variation than asexual reproduction. यह explain कर सकते हैं कि sexual reproduction में asexual reproduction के मुकाबले ज्यादा genetic variation (आनुवंशिक विविधता) क्यों होती है।
Construct a 2x2 Punnett square for a monohybrid cross and calculate phenotypic (3:1) and genotypic (1:2:1) ratios. Monohybrid cross के लिए 2x2 Punnett square बना सकते हैं और phenotypic (3:1) और genotypic (1:2:1) ratios calculate कर सकते हैं।
Explain how traits assort independently in a dihybrid cross to yield a 9:3:3:1 ratio. यह explain कर सकते हैं कि dihybrid cross में traits independently inherit होकर 9:3:3:1 ratio कैसे बनाते हैं।
Trace the molecular path from DNA genes to physical characteristics. DNA genes से physical characteristics के expression के पूरे molecular pathway को trace कर सकते हैं।
Diagram the chromosomal cross (XX x XY) that determines human biological sex. Chromosomal cross (XX x XY) का diagram बना सकते हैं जो humans में sex determination को explain करता है।