(i) Explain monohybrid cross taking seed coat colour as a trait in Pisum sativum. Workout the cross upto $F_{ 2 }$ -generation.
(ii) State the laws of inheritance that can be derived from such a cross.
(iii) How is the phenotypic ratio of $F_{ 2 }$-generation different in a dihybrid cross?
(i) In a monohybrid cross, when homozygous dominant and homozygous recessive parents are crossed, F_{ 1 }-hybrid would be heterozygous for the trait and would express the dominant allele.
(ii) The hybrid is heterozygous containing both alternative
alleles (Y and y) but only one trait, i.e. yellow colour appeared and green colour trait is suppressed in F_{ 1 } generation. This shows that yellow seed colour is dominant over the green seed colour trait. This explains Mendel’s law of dominance.
(iii) Phenotypic ratio in F_{ 2 }-generation, Yellow seeds :
Green seeds, (3 : 1) in monohybrid cross and in dihybrid cross 9 : 3 : 3 : 1.