What is inbreeding and whats not?

here's a start in in line breeding and breeding sisters to brothers.

i hope tim doesn't get mad that i posted this but i'm sure he'd rather all of us get educated.

Lets say a person crosses rooster A with hen B. An organism can only
give 50% of its genes to its offspring. The F1 offspring will have 50%
of roosters A's genes and 50% of hen B's genes. So the F1 are 50A/50B.
If a person crosses two F1 50A/50B x 50A/50B (producing F2), then the
F1 rooster can only give 25% of the A genes to the F2 and the hen will
provide 25% of the A genes also, equalling 50% A genes in the F2 the
same is true for the B genes. The F2 offspring are 50A/50B just like
the F1 parents.

If a person back crosses the F1 50A/50B to Rooster A (100% A), then
the formula changes and the offspring are more like the rooster
genetically- 75%A/25%B. If a person back crosses to the hen- then the
offspring are more like her 25%A/75%B.

The problem arises when there are unwanted genes that are recessive in
a flock.

If a person crosses two birds that are carriers of a recessive gene(
they do not express the trait), they can have chicks that do not have
the trait and chicks that do have the trait. You cull the birds that
have the trait. Some of the birds that do not have the trait will be
carriers so they can pass the gene on to their offspring. Some of the
offspring will not even carry the gene so they can not even give the
gene to their offspring. You can eliminate the trait from your flock
by crossing siblings or you can encourage the trait by crossing
siblings but you cull the bad birds.

Culling is the key to inbreeding. Once a breeder has a flock that is
genetically homogeneous then a breeder must out cross to improve
traits. Lets say a person is wanting to improve a specific trait, and
the breeder crosses a specific male to a specific female and hatches
30 eggs from the crossing and none of the chicks have improved on the
trait- then genetically there is nothing to be gained by crossing the
two again. A breeder will have to out cross to get the gene or genes
needed to improve the trait.

 

I had a professor in my veterinary classes in college who said, "It's linebreeding when it works & inbreeding when it doesn't."