Define key terms (gene, allele, genotype, phenotype)

3.1.1 · Biology › Mendelian Genetics

1. Gene

KYA HAI: Chromosome par ek aisi location jo ek characteristic control karti hai — jaise "flower colour ka gene" ya "seed shape ka gene."

YEH KYUN IMPORTANT HAI: Mendel ko DNA ke baare mein nahi pata tha, lekin unhone reason kiya ki kuch discrete "factors" zaroor hone chahiye jo pure pass hote hain, blend nahi hote. Hum ab in factors ko genes kehte hain.

KAISE PEHCHANO: Gene ek trait ki category hai (flower colour). Yeh chromosome par ek fixed jagah par rehta hai jise locus kehte hain (plural: loci).

2. Allele

KYA HAI: Agar gene "flower colour" hai, toh alleles ho sakte hain purple (P) aur white (p).

KYUN: Diploid organisms mein har gene ki do copies hoti hain (ek har parent se), ek-ek homologous chromosome par. Yeh do copies same allele ho sakti hain ya alag alleles bhi.

KAISE LIKHTE HAIN: Capital letter = dominant allele (jaise $P$ ). Lowercase = recessive allele (jaise $p$ ).

Homozygous = do identical alleles ( $P P$ ya $pp$ ). "Homo" = same.
Heterozygous = do alag alleles ( $P p$ ). "Hetero" = different.

3. Genotype

KYA HAI: Flower colour ke liye genotype in mein se ek hoga: $P P$ , $P p$ , ya $pp$ .

PHENOTYPE SE ALAG KYUN HAI: Kyunki ek hidden (recessive) allele genotype mein tab bhi exist karta hai jab uska effect dikh nahi raha. $P p$ white carry karta hai lekin dikhta purple hai.

KAISE PADHEIN: Har gene ke liye do letters (diploid). Har letter ek chromosome par ek allele hai.

4. Phenotype

KYA HAI: "Purple flowers" ya "white flowers." Height, colour, blood type — kuch bhi jo aap observe kar sako.

GENOTYPE ≠ PHENOTYPE KYUN: Dominance ka matlab hai ek allele doosre ko mask kar sakta hai. Toh alag genotypes same phenotype de sakte hain:

$P P \to purple, P p \to purple, pp \to white$

Yahan $P P$ aur $P p$ do genotypes hain, ek phenotype.

ENVIRONMENT KAISE GHUS AATA HAI: Phenotype = genotype + environment. Ek plant jiske paas "tall" genes hain lekin paani nahi mila, woh chhota reh sakta hai. Toh phenotype expression hai, sirf code nahi.

Figure — Define key terms (gene, allele, genotype, phenotype)

Scratch se derivation: "2 genotypes → 1 phenotype" kyun zaroor hota hai

Apni galtiyon ko steel-man karo

Worked examples

Recall Feynman: 12-saal ke bachche ko samjhao (click to reveal)

Socho har pea plant ke paas flower colour ke liye ek chhoti si instruction card hai. Card slot gene hai. Us par jo words likh sakte hain — "purple" ya "white" — woh alleles hain. Tumhe do cards milte hain, ek mum se, ek dad se. Jo exact pair tum pakde ho (purple+white, ya white+white) woh tumhara genotype hai. Flower actually jis colour ka nikalta hai woh tumhara phenotype hai. Trick: ek "purple" card pakad lena kaafi hai flower ko purple banane ke liye — purple boss hai (dominant), isliye woh white card ko chhupaata hai. Isliye do plants same colour ke dikh sakte hain lekin secretly alag cards pakde ho sakte hain!

Active recall flashcards

Gene kya hai?

Heredity ki ek unit — DNA ka ek stretch jo ek fixed locus par hota hai aur ek particular trait ke liye code karta hai.

Allele kya hai?

Gene ka ek variant (alternative form), jaise flower colour ke liye purple vs white.

Gene vs allele ek line mein?

Gene = sawaal/trait category; allele = ek possible jawab/version.

Genotype kya hai?

Alleles ka complete set jo ek organism carry karta hai (uska genetic makeup), jaise Pp.

Phenotype kya hai?

Genotype plus environment se milne wala observable trait, jaise purple flowers.

Homozygous vs heterozygous?

Homozygous = do identical alleles (PP ya pp); heterozygous = do alag alleles (Pp).

Do organisms same phenotype share karte hue genotype mein alag kyun ho sakte hain?

Dominance recessive allele ko mask karta hai, isliye PP aur Pp dono purple dikhte hain.

Pp × Pp ke liye genotype aur phenotype ratios batao.

Genotype 1 PP : 2 Pp : 1 pp; phenotype 3 purple : 1 white.

Kya "dominant" ka matlab stronger ya more common hai?

Nahi — iska sirf matlab hai ki present hone par yeh express hota hai (doosre allele ko mask karta hai).

2 alleles wale ek single gene se kitne genotypes bante hain?

Teen (AA, Aa, aa), n(n+1)/2 se n=2 ke saath.

Phenotype equation words mein?

Phenotype = genotype + environment.

Connections

Law of Segregation — kyun har parent exactly ek allele per gamete pass karta hai
Law of Independent Assortment — multiple genes ko combine karna
Dominant and Recessive Alleles — phenotype genotypes ko kaise collapse karta hai
Punnett Squares — genotype/phenotype ratios predict karne ka tool
Homologous Chromosomes — kyun diploids har gene ke liye do alleles carry karte hain
Incomplete Dominance and Codominance — jab genotype ≠ phenotype rules change ho jaate hain