Question

Define or explain the following terms: 

i. Genotype

ii. Phenotype 

iii. Monohybrid cross

iv. Dihybrid cross 

v. Monohybrid

vi. Monohybrid ratio

Answer 1

i. Genotype: It is the genetic constitution of an individual with respect to a single character or a set of characters. e.g. Tall (TT or Tt), Dwarf (tt).

ii. Phenotype: The external appearance of an individual for a given trait. e.g. tallness, dwarfness.

iii. Monohybrid cross: A cross between two pure (homozygous) parents differing in a single pair of contrasting character is called monohybrid cross. The ratio for this cross is 3 : 1.

iv. Dihybrid cross: A cross between two pure parents differing in two pairs of contrasting characters is called dihybrid cross. The ratio for such cross is 9 : 3 : 3 : 1.

v. Monohybrid: It is heterozygous for one trait and produced by crossing two pure parents differing in a single pair of contrasting characters. eg. Cross between pure tall (TT) and dwarf (tt) parent gives rise to hybrid tall (Tt).

vi. Monohybrid ratio: The phenotypic ratio of different types of offsprings (dominant and recessive) obtained in F₂ generation of a monohybrid cross is called Monohybrid ratio. In all Mendelian crosses, the monohybrid ratio is 3 : 1.