Class X Biology - Chapter: Genetics and Evolution - Topic: Mendelian Genetics Numerical Problems

Problem 1: Monohybrid Cross

In pea plants, tall (T) is dominant over dwarf (t). If a homozygous tall pea plant is crossed with a homozygous dwarf pea plant, what will be the phenotypic and genotypic ratios of the F1 generation?

Solution:

• Parental Generation (P): Homozygous Tall (TT) x Homozygous Dwarf (tt)
• Gametes: T, t
• F1 Generation: All Tt (Tall)

Phenotypic Ratio: All Tall (100% Tall) Genotypic Ratio: All Heterozygous (100% Tt)

Problem 2: Dihybrid Cross

In pea plants, round seeds (R) are dominant over wrinkled seeds (r), and yellow seeds (Y) are dominant over green seeds (y). If a pea plant heterozygous for both traits (RrYy) is self-pollinated, what will be the phenotypic ratio of the offspring?

Solution:

This is a dihybrid cross. The gametes produced by RrYy will be RY, Ry, rY, ry.

Using a Punnett Square (16 squares):

Phenotypes and their counts:

• Round, Yellow (R_Y_): 9 (RRYY, RRYy, RrYY, RrYy)
• Round, Green (R_yy): 3 (RRyy, Rryy)
• Wrinkled, Yellow (rrY_): 3 (rrYY, rrYy)
• Wrinkled, Green (rryy): 1 (rryy)

Phenotypic Ratio: 9 (Round, Yellow) : 3 (Round, Green) : 3 (Wrinkled, Yellow) : 1 (Wrinkled, Green)