The most extreme form of inbreeding is selfing, that is, the mating of an individual to itself. Suppose a plant has genotype Bb for some part of its chromosome structure. Since germ cells contain a sample half of the plant's genetic material, half would contain B, and half b for both male and female cells. If those offspring were mated to themselves, only BB offspring would result from BB individuals, and bb offspring from bb individuals. Dairy cattle don't self, but the same process of increasing the frequency of homozygotes occurs at a slower rate.
Consequences Inbred animals become homozygous at more chromosome locations than non-inbreds.
The positive aspect of inbreeding is that the genotypes of sperm or egg cells are more predictable than for outbreds. If the inbred were superior and transmitted its superiority with regularity, the advantages would be obvious. Unfortunately, inbreeding produces many undesirable side effects. If the individual does survive, it may be totally unprofitable. With inbreeding, these genes appear with greater frequency as homozygotes - the gene frequencies don't change but the number of homozygotes increases.