Question

In cattle, the gene for black colour (B) is dominant over the gene for white (b).
A hybrid cow is crossed with a white bull.
1.1 Use the Punnet square to show the genotype of the F1 generation.
BR
BB
bbbb
B​

Answer 1

Answer:

A Punnett square for a cross between two heterozygous snapdragons will predict the genotypes RR, Rr, and rr in a 1:2:1 ratio, and since these alleles display incomplete dominance, the phenotypes will be red, pink and white in a 1:2:1 ratio.

Answer 2

We know that Black is dominant over the white , so any allele of Black (B) will be dominant over any allele of white (b) .

Now , when hybrid cow ( Bb) is crossed with white (bb) bull , the punnet square will be as :

$\begin{tabular}{c|c|c|} Alleles & B & b \\ \cline{1-3}b & Bb & bb \\ \cline{1-3} b & Bb & bb \\ \cline{1-3}\end{tabular}$

Hence progeny will be Bb ( Hybrid Black) and bb ( pure white) in the ratio 1:1 both phenotypically as well as genotypically.

This is also an example of test cross .

• In a test cross , a recessive parent is crossed with another parent. If the progeny ratio comes out to be 50% , the another parent was heterozygous .
• If it comes out to be 100% , the another parent was homozygous dominant.