-zygous (pronounced zeye-guss) means two letters when used with homo- and hetero-

We now know hetero and homo. But heterozygous means two different letters (alleles), a capital or lower case and homozygous means the same two letters (alleles).

Zygous is the pairing of chromosomes with homo and hetero used to define the pairing

The gust (-zygous) of wind blew away two letters.

Example

In the punnett square, which graphically illustrates the basic rules of heredity, letters are used to depict the trait from the sex cells of each parent. In this example the mother has brown eyes but carries one brown allele and one blue allele. The father also has brown eyes but again carries one blue allele and one brown allele.

Homozygous means the same alleles but a heterozygous pairing means one allele is dominant to the other

BB = homozygous (same two letters) or homozygous dominant

Bb = heterozygous (different two letters)

bB = heterozygous (different two letters)

bb = homozygous (same two letters) or homozygous recessive

For recessive and dominant press here.