In a homozygous plant, round seeds (R) are dominant over wrinkled seeds (r): [5 MARKS]
(a) Draw a Punnett square to show the gametes and offspring when both the plants have heterozygous round seeds (Rr).
(b) Mention the Phenotype and Genotype ratios of the offsprings in F2 generation.
(c) Name the sex chromosomes in human males and females.
(d) Briefly explain the term 'Mutation'.
(e) What is the number of chromosomes in the gametes of human beings?

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Solution

Each Part: 1 Mark

(a)
(i) Rr $$ Rr

(b) $F_{2}$ generation
1. RR $$ RR
Phenotypic ratio - 4:0 (all round)
Genotypic ratio - 4:0 (all homozygous round)
2. Rr $$ Rr
Phenotypic ratio - 3:1 (3 round, 1 wrinkled)
Genotypic ratio - 1:2:1 (1 homozygous round, 2 heterozygous round, 1 wrinkled seed)
3. rr $$ rr
Phenotypic ratio - 4:0 (all wrinkled)
Genotypic ratio - 4:0 (all homozygous wrinkled)

(c) Males - XY Females - XX

(d) Mutation is a sudden change in one or more genes, or in the number or in the structure of chromosomes.

(e) The number of chromosomes in the gametes of human beings 23.

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