Question 1

In a monohybrid cross between heterozygous tall (Tt) pea plants, what is the phenotypic ratio of the offspring?

Accepted Answer

Answer: The phenotypic ratio is 3 tall : 1 dwarf. In a Tt × Tt cross, the genotypic ratio is 1 TT : 2 Tt : 1 tt, and since both TT and Tt show the tall phenotype, three out of four plants are tall and one is dwarf. Explanation: TT → Tall Tt → Tall tt → Dwarf Thus, the phenotypic ratio = 3 tall : 1 d

Question 2

Which of the following is an example of a sex‑linked trait in humans?

Accepted Answer

Answer: Colour blindness is a classic X‑linked recessive trait in humans. Explanation: The gene responsible is located on the X chromosome. Males (XY) who inherit the defective allele on their single X chromosome express the condition, while females (XX) need two copies to be affected. Other options

Question 3

According to Mendel’s law of segregation, alleles separate during which stage of meiosis?

Accepted Answer

Answer: Alleles separate during Anaphase I of meiosis. Explanation: In Anaphase I, homologous chromosomes are pulled to opposite poles, causing the two alleles of a gene (present on each homolog) to move into different daughter cells. This ensures each gamete receives only one allele for each gene.

Question 4

In a dihybrid cross between heterozygous plants (RrYy × RrYy) where R = round, r = wrinkled, Y = yellow, y = green, what is the phenotypic ratio of the F₂ generation?

Accepted Answer

Answer: The phenotypic ratio is 9 : 3 : 3 : 1. Explanation: The classic Mendelian dihybrid cross yields nine plants showing both dominant traits (round‑yellow), three showing round‑green, three showing wrinkled‑yellow, and one showing wrinkled‑green.

Question 5

If a homozygous recessive individual (aa) is crossed with a heterozygous individual (Aa), what proportion of the offspring will be heterozygous?

Accepted Answer

Answer: 50 % of the offspring will be heterozygous (Aa). Explanation: The Punnett square shows two possible genotypes: 1 aa and 1 Aa. Hence, half (2 out of 4) are Aa.

Heredity — NCERT Class 10 Science Important Questions & Revision Notes