Aberdeen Angus cattle are black BB and polled no horns PP Re

Aberdeen Angus cattle are black (BB) and polled (no horns) (PP). Red shorthorn cattle are red with horns (bb pp). Black (B) and polled (P) are dominant. What will be the F2 ratios of a cross between BBPP times bbpp? A test cross with a Black Polled cow of unknown genotype of gives 2 black polled cows and two black horned. What is the genotype of the unknown parent?

Solution

Answer:

8. (a) Homozygous dominant (BBPP) and homozygous recessive (bbpp), all the F1 offspring will be heterozygous BbPp.

The dihybrid cross: BbPp x BbPp. It leads to 9:3:3:1 phenotype ratio.

9 gives dominant traits
3 gives a combination of B_pp (Bb or BB)
3 gives a combination of bbP_ (PP or Pp)
1 gives bbpp in recessive condition.

So, the cross gives:

9 black polled: 3 black horned: 3 red polled: 1 red horned

(b) The genotype of the unknown parent is BBPp.

The cross: BBPp * bbpp , which gives black polled and black horned in the ratio 1:1.