Question

Short / Long answer type questions.
Explain a monohybrid cross taking seed Coat colour as a trait in Pisum sativum. Work out the cross up to F2 generation. (b) State the laws of inheritance that can be derived from such a cross. (c) How is the phenotypic ratio of F2 generation different in a dihybrid cross?

Answer 1

F${}_2$ generation	Y	y
Y	YY (yellow)	Yy (yellow)
y	Yy (yellow)	yy (green)

(a) Yellow seed coat colour (YY) is dominant over green seed coat colour (yy).

YY $\ast$ yy $\to$ Yy (F${}_1$ generation produced all have yellow seed coat color).

F${}_2$ generation produced have phenotypic ratio 3: 1 and genotypic ratio 1: 2: 1.

(b) The law which can be derived from this cross is the law of segregation. This can be inferred that both the plants produce gametes and the alleles segregate from each other such that only one allele is transmitted to a gamete. The segregation is a random process so there is a 50 percent chance of a gamete containing either Y or y allele.

(c) Dihybrid cross, phenotypic ratio: 9: 3: 3: 1.

Monohybrid cross, phenotypic ratio: 3: 1.