Heredity: How Traits Pass from Parents to Offspring: 15 MCQs with answers

C · Heredity

Heredity is the transmission of traits from parents to offspring; genetics is the study of heredity and variation.

B · Alleles

Alleles are the alternative forms of a gene, such as T and t for plant height.

D · Two

Each organism carries two alleles per gene, one inherited from each parent.

C · Heterozygous

Tt has two different alleles, so it is heterozygous.

A · True

Mendel's monohybrid F₂ generation shows a phenotypic ratio of 3:1 (dominant : recessive) and a genotypic ratio of 1:2:1.

C · 1/4

The cross gives 1 TT : 2 Tt : 1 tt, so 1/4 are tt (short).

A · Law of Segregation

The Law of Segregation states that the two alleles separate during gamete formation, so each gamete carries one allele.

B · 9:3:3:1

Mendel's dihybrid cross gave a 9:3:3:1 phenotypic ratio in the F₂ generation.

B · 1:2:1

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

D · They receive a unique combination of alleles from each parent.

The correct option is B. Siblings inherit a unique combination of alleles from each parent, which leads to different phenotypes. This genetic variation is a result of the segregation of alleles during gamete formation, allowing for diverse traits to be expressed.

D · Phenotype depends on genotype and environment.

Phenotype = genotype + environment; identical genotypes can produce different phenotypes under different environmental conditions.

D · Recessive traits need two copies to show but can be common.

Recessive simply means the trait requires two recessive alleles to be expressed; it does not imply rarity or harm.

D · A dihybrid cross of round-yellow × wrinkled-green

Independent assortment is observed when two traits are tracked together, as in a dihybrid cross producing a 9:3:3:1 ratio.

D · Heredity and Mendelian inheritance

Breeders use heredity principles, including Mendelian inheritance, to select and combine desirable traits such as disease resistance.

A · 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green

The correct phenotypic ratio of a dihybrid cross (RrYy × RrYy) is 9:3:3:1, where 9 offspring will have round yellow seeds, 3 will have round green seeds, 3 will have wrinkled yellow seeds, and 1 will have wrinkled green seeds. This is a result of the independent assortment of alleles during gamete formation.