Heterozygous & Homozygous
The unfamiliar words, e.g., heterozygous, homozygous and hemizygous, are inescapable when trying to establish precisely what is being discussed. Following are some definitions that may help with the derivation of these words.
- A zygote is: the cell formed by the union of two gametes (sperm and ovum).
- The suffix -zygous implies: a zygotic constitution of a specified kind.
- The prefix hetero- means: different (or, not alike).
- The prefix homo- means: same (or, alike).
- The prefix hemi- means: half (or, partial).
- The term heterozygous means: having dissimilar genes at corresponding loci.
- The term homozygous means: having identical genes at corresponding loci.
- The term hemizygous means: having no allelic counterpart; unpaired gene at a locus; - (typical of the sex-linked genes in female pigeons).
Note: The versatility of a pencil is lost when using a typewriter. For example: the numeric fraction one-fourth is express as 1/4 when typewritten on the same line. For expressing typewritten genotypes the adoption of the forward slash "/" is used to represent an unpaired chromosome, and a double-slash "//" to represent paired chromosomes. Gene symbols are typewritten adjacent to their respective chromosome. The genotype of a brown cock that is heterozygous for reduced is written - "rb//+b". Please note - the "+" symbol in the genotype is used to express a wildtype gene opposing the reduced "r" gene - at the reduced locus.
Following are some genotypes for sex-linked genes only:
Genotype: Sex: Phenotype: Description: BA//+ cock ash-red heterozygous for ash-red b//+ cock wildtype heterozygous for brown +//r cock wildtype heterozygous for reduced BA//BA cock ash-red homozygous for ash-red b//b cock brown homozygous for brown r//r cock reduced homozygous for reduced d//d cock dilute homozygous for dilute d+//db cock dilute homozygous for dilute & heterozygous for brown rb//+b cock brown heterozygous for reduced & homozygous for brown db//db cock dilute-brown homozygous for dilution & brown BA/. hen ash-red hemizygous for ash-red b/. hen brown hemizygous for brown dBA /. hen dilute-ash-red hemizygous for dilute & ash-red db/. hen dilute-brown hemizygous for dilution & brown