If you mate a Hereford bull with horns to a female without horns if the female is homozygous for the no horns how many calves could be born without horns Why?

Answer 1

This is not a matter of how many it's a matter of chance in terms of percentages. In this example, any bull that is horned is ONLY homozygous, both phenotypically AND genotypically, for horned because the horned gene in cattle is recessive. The polled (non-horned) characteristic in cattle is a dominant trait both phenotypically and genotypically. So that means that any horned parent that breeds a homozygous polled parent will have offspring that are ALL polled. The only way you will get horned offspring is one of two ways: a horned sire mates with a horned dam, or, a hetero polled sire mates with a hetero polled dam (resulting in a much smaller chance than the first way). The question above is answered as followed:

Homozygous Horned (Hereford) bull x Homozygous Polled female = 100% Polled offspring.

I cannot use the Punnett square on this site, but if you use it on a piece of paper you will see that 100% of all offspring are polled. But notice that genotypically they are HETEROZYGOUSLY polled. This means they are polled physically, but in their genes their offspring have a 50% chance, should this offspring be bred to a horned partner, of having either horned offspring or polled offspring. If the offspring of the above cross were bred to a polled partner, the results would be 50% hetero polled and 50% homozygously polled. AND, if the above offspring were bred also to a hetero polled partner, you would get, phenotypically, 75% polled and 25% horned. Genotypically, this is 25% homozygously polled, 50% hetero polled, and 25% homozygously horned.

See, the most a cow can have in her lifetime is 20 calves. There is no way that she can have 100 or so calves in her lifetime to see this example work out. Producers have to go by chances of an event happening when selectively breeding cattle, not how many.