In genetics, what are homozygous and heterozygous genes, and are they alternate for each other?Reference link:...

There were actually three different genes questions at the
link you supplied. When an organism has two of the same genes for a trait, this
condition is known as homozygous. When an organism has two
different genes for a trait, this is called heterozygous.
The alternate genes for a particular trait are called
alleles. An example of various alleles for the same trait
are the alleles for blood type. There is an allele for A, for B, and for O. The
recessive allele is O and A and B alleles are codominant. So, for blood type, a person
could be homozygous, if their gene combination is AA, BB, or OO. However, if a person
has the gene combinations-- AO, BO or AB, they would be heterozygous for that particular
trait.