Heredity: Dihybrid cross

The expected phenotypic ratio obtained by crossing the F1 generation in dihybrid cross would be?

• 3:1

• 1:2:1

• 9:3:3:1

• 1:2:1:2:4:2:1:2:1

Answer explanation

The phenotypic ratio obtained by the dihybrid cross is 9:3:3:1 while that by a monohybrid cross is 3:1. The genotypic ratio of a monohybrid cross is 1:2:1 while the genotypic ratio of dihybrid cross would be 1:2:1:2:4:2:1:2:1.

Mendel took _______ contrasting characteristics of pea plants.

• eight

• seven

• six

• five

Answer explanation

Mendel used seven contrasting characters of traits in pea plants:

Pea shape: Round or Wrinkled.

Pea color: Green or Yellow.

Pod shape: Constricted or Inflated.

Pod color: Green or Yellow.

Flower color: Purple or White.

Plant size: Tall or Dwarf.

Position of flowers: Axial or Terminal.

Which of the Mendelian law can be studied using a dihybrid cross but not a monohybrid cross?

• Law of Segregation

• Law of Linkage

• Law of Independent Assortment

• Law of Dominance

Answer explanation

The Law of Independent Assortment states that during a dihybrid cross (crossing of two pairs of traits), an assortment of each pair of traits is independent of the other. In other words, during gamete formation, one pair of trait segregates from another pair of traits independently.

If the parent generation shows one homozygous recessive parent and one homozygous dominant parent, what kind of offsprings does the F1 generation show?

• Homozygous dominant

• Heterozygous recessive

• Heterozygous dominant

• Homozygous recessive

Answer explanation

The offsprings shown by the homozygous recessive and homozygous dominant parent in the F1 generation will all be heterozygous dominant. (Law of Dominance)

While constructing a Punnett square for a Dihybrid cross, How many combinations will be seen in the F2 generation?

• 16

• 14

• 12

• 20

Answer explanation

There will be total 4x4 squares, that is equal to 16 squares. 16 possible combinations.