Question

A homozygous polled Hereford bull (with dominant hornless gene (PP) , dominant white-face spotting pattern (WW) and recessive brown coat color (bb) is crossed to an Angus female with horns (recessive, pp), no spots (recessive, ww) and a dominant solid black coat color (dominant, BB). All the F1 animals are polled (hornless), have a solid black coat and a white-face spotting pattern. These three loci are autosomal and independent from each other. The F1 animals are crossed to F1 animals to produce an F2. How often are horned, white-face and black animals expected in the F2?

Answer 1

the parental cross is

PPWWbb * ppwwBB

PpWwBb (F1)

the F1 cross is

PpWwBb * PpWwBb

le`s divide this into 3 different crosses

Pp * Pp

	P	p
P	PP (hornless)	Pp(hornless)
p	Pp(hornless)	pp ( horned)

the proportion of horned animals= number of horned animals/total number=1/4

Ww * Ww

	W	w
W	WW (white-face spotting)	Ww (white-face spotting)
w	Ww (white-face spotting)	ww ( no spotting)

the proportion of white face animal= number of white-faced animals/total number=3/4

Bb * Bb

	B	b
B	BB (black coat color)	Bb (black coat color)
b	Bb (black coat color)	bb (brown coat color)

the proportion of animals with black coat colour= number of animals with black coat colour/total number=3/4

so frequency of  horned, white-face and black animals in the F2= proportion of horned animals proportion of white face animal proportion of animals with black coat colour= 1/43/43/4=9/64

frequency of  horned, white-face and black animals in the F2=9/64