Final answer:
Inbreeding increases homozygosity of loci leading to inbreeding depression, while outbreeding introduces heterozygosity which can improve genetic diversity and population fitness.
Step-by-step explanation:
Inbreeding and outbreeding affect genetic loci in different ways. Inbreeding tends to increase the homozygosity of loci, which means that there is a higher chance for offspring to inherit two identical alleles for a given gene. This can lead to the expression of deleterious recessive mutations and a reduction in overall fitness, a phenomenon known as inbreeding depression. In contrast, outbreeding (or outcrossing) introduces greater heterozygosity at loci because it involves mating between genetically unrelated individuals, which can increase genetic diversity and potentially improve population fitness by including new, beneficial alleles into the gene pool.
A breeder may avoid inbreeding because it can result in undesirable traits becoming more common, such as the expression of deleterious recessive alleles, and can prevent gene flow which brings new, advantageous genes into the population. Meanwhile, outbreeding can help maintain or increase genetic diversity, which is important for the adaptive potential of a population or species. Measuring the levels of heterozygosity is one way to gauge genetic diversity, and populations with more alleles typically have higher genetic diversity.