Homozygosity is the condition of having two identical alleles from the parents for a gene (AA). Heterozygosity is the condition of having two different alleles for a trait from parents (Aa).

LOH stands for Loss of Heterozygosity. LOH happens when a somatic cell consist only of one copy of allele caused by non-disjunction in mitosis, segregation all through out re-combination, or during chromosome segment deletion.

F = 1-observed frequency(Aa)/expected frequency(Aa)

As alleles become fixed, there is an overall decline in heterozygosity as each population become homozygous for one or the other of the alleles.

Codominance. It's the case of AB blood types, for instance. Neither trait is dominant over the other, so both manifest.