Animal Science

Breeding & Genetics

Original Power Point Created by Casey Osksa

Modified by Georgia Agricultural Education Curriculum Office

June 2002

Genetics Terms• Heterozygous = two different types of

genes (Bb)• Homozygous = two similar genes

(BB)• Dominant Gene = trait overpowers

others• Recessive Gene = must be

accompanied with another recessive gene to express trait

• Incomplete Dominance = both traits express themselves

Punnet Square

• Shorthorn Cattle• R = Red• W = white• RW = roan• If a red bull (RR) is mated to a

white cow (WW), what color will the calves be?

Punnet Square

R R

W

W

RW RW

RW RW

Punnet Square

• If a red bull (RR) is mated to a roan (RW) cow, what color will the calves be?

Punnet Square

R R

R

r

RR RR

Rr Rr

Punnet Square

• P = horned• p = polled• If a homozygous horned cow (PP) is

mated to a homozygous polled bull (pp), what percent of the calves will be horned, polled?

Punnet Square

P P

p

p

Pp Pp

Pp Pp

Punnet Square

• If a homozygous horned cow (PP) is mated to a heterozygous horned bull (Pp), what percent of the calves will be polled?

Punnet Square

P P

p

p

Pp Pp

Pp Pp

Punnet Square

• Mate an Angus bull that is homozygous black and polled (BBPP) to a red shorthorn cow which is homozygous red and horned (bbpp).

• What is the probability that the offspring will be black? Polled? Horned? Black and Polled?

Punnet SquareBP BP

bp

bp

BbPp BbPp

BbPp BbPp

Black = 100%Polled = 100%Horned = 0%Black & Polled = 100%

Punnet Square

• Now mate two of the offspring which are heterozygous for black/red and polled/horned (BbPp)

• What is the probability that the offspring will be black? Black Polled? Black Horned? Red? Red Polled? Red Horned?

Punnet Square

• How do you do a punnet square with multiple genes?

• Use all possible gene combinations• BbPp = could be BP, Bp, bP,bp• 4 x 4 grid

Punnet SquareBP Bp bP bp

BP

Bp

bP

bp

BBPP BBPp BbPP BbPp

BBpP BBpp BbPp Bbpp

BbPP BbPp bbPP bbPp

BbPp Bbpp bbPp bbpp

Punnet Square

• Black = 12 out of 16 or 75%• Black Polled = 9 out of 16 or 56.25%• Black Horned = 3 out of 16 or

18.75%• Red = 4 out of 16 or 25%• Red Polled = 3 out of 16 or 18.75%• Red Horned = 1 out of 16 or 6.25%

Punnet Square

• Mate a heterozygous bull (BbPp) to a homozygous cow (BBPP)

• What are the outcomes?

Punnet Square

BP Bp bP bp

BP BBPP BBPp BbPP BbPp

Punnet Square

• Mate a (BbPp) bull to a (BBPp) cow• what are the outcomes?

Punnet Square

BP Bp bP bp

BP

Bp

BBPP BBPp BbPP BbPp

BBPp BBpp BbPp Bbpp