Genetics - Some Basic Fundamentals

  • Question

    In a homozygous plant round seeds (R) are dominant over wrinkled seeds (r):

    i. Draw a Punnett square to show the gametes and offspring when both the

    plants have heterozygous round seeds (Rr).

    ii. Mention the Phenotype and Genotype ratios of the offspring in F2 generation.

    iii. Name the sex chromosomes in human males and females.

    iv. Briefly explain the term ‘Mutation’.

    v. What is the number of chromosomes in the gametes of human beings?


    i. Parents: Rr x Rr 

      R r

    RR Rr
    r Rr rr

    Gametes: R, r; R, r
    Offspring: RR (Round); Rr (Round); rR (Round); rr (Wrinkled)


    ii.   Phenotypic ratio: 3:1
    Genotypic ratio: 1:2:1

    iii.  Sex chromosomes in human males: XY and human females: XX

    iv. Mutation is a sudden change in one or more genes or in the number or in the structure of chromosomes.

    v.   The number of chromosomes in human gametes is 23 (22 autosomes and 1 sex chromosomes)

    NCERT Book Store

    NCERT Sample Papers

    Entrance Exams Preparation