Heredity and Evolution — Class 10 NCERT Chapter 8: 17 MCQs with answers

A · Heredity

Heredity is the transmission of traits from parents to offspring, while variation refers to differences among individuals.

B · Tall

T (tall) is dominant over t (dwarf), so a Tt plant shows the dominant tall phenotype.

D · 1:2:1

The F2 genotypic ratio is 1 TT : 2 Tt : 1 tt, i.e., 1:2:1.

D · 3:1

Three tall (TT or Tt) to one dwarf (tt) gives a 3:1 phenotypic ratio.

B · XY

Males have one X and one Y chromosome (XY); females are XX.

A · True

Mendel's monohybrid cross on pea plants produced a 3:1 phenotypic ratio in the F2 generation.

D · 50%

Each birth is an independent event; the probability of a boy remains 50% regardless of previous children.

D · An individual with one dominant and one recessive allele who shows the dominant trait

A carrier is heterozygous (e.g., Tt) and shows the dominant phenotype but can pass the recessive allele to offspring.

B · 25%

The cross Tt × Tt gives TT, Tt, Tt, tt; only tt (1 out of 4) shows the recessive trait, so probability is 25%.

B · 9:3:3:1

Mendel's dihybrid cross produced four phenotypes in a 9:3:3:1 ratio, showing independent assortment.

C · Carriers show the dominant trait but can pass the recessive allele to offspring.

Heterozygous carriers (Tt) do not show the recessive trait but can transmit the recessive allele, allowing it to reappear in later generations.

B · 50%

The cross Tt × tt gives Tt and tt in equal numbers, so 50% are dwarf (tt).

A · A dominant allele expresses itself even when only one copy is present.

Dominance refers to expression when one copy is present, not to frequency or disease status.

A · 3 tall : 1 dwarf

The Punnett square gives TT, Tt, Tt, tt; three show tall and one shows dwarf, so 3:1.

C · She must be heterozygous (Ee).

To have a child with attached earlobes (ee), the mother must contribute an e allele; since she has free earlobes, she must be Ee.

D · It generates genetic variation, which is the raw material for natural selection.

Sexual reproduction reshuffles alleles, creating variation that helps populations adapt to changing environments.

B · 9:3:3:1

The correct option is 9:3:3:1 because this ratio represents the expected phenotypic outcomes when two traits are independently assorted during a dihybrid cross, as demonstrated by Mendel's experiments.