Question

Five Mark Questions :
(a) A true breeding homozygous Pea plant with green pods and axial flowers as dominant characters is crossed with a recessive homozygous Pea plant with yellow pods and terminal flowers. Work out the cross upto $F_2$ generation giving the phenotypic ratios of $F_1$ and $F_2$ generations respectively.
(b) State the Mendelian principle which can be derived from such a cross and not from monohybrid cross.

Answer 1

Monohybrid cross is generally the cross between a single pair of contrasting characters. And a dihybrid cross is the one which involves two pairs of contrasting traits.

The Mendelian law that can be seen from the dihybrid cross is the law of segregation of gametes which states that when a pair of contrasting factors of genes get together in heterozygous condition the two members of the allylic pair remain together without been contaminated and when the gametes are formed from the hybrid, the two separate out from each other and only one enters each gamete as seen in monohybrid and dihybrid cross. That is why the law of segregation is also termed as the law of purity of gametes.

Law of independent assortment

If the inheritance of more than one pair of characters is studied simultaneously the factor of genes for each pair of characters a sort out independently of another pair. Mental formulated this law from the result of a dihybrid cross.