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UNDERSTANDING BASIC breeding and genetic terms is not extremely difficult. However, if it is not something you use every day, hearing or reading a word or phrase can leave a person scratching their head and saying, “Huh?” In the world of poultry breeding, there are some basic genetic and breeding terms that you may hear. While not all inclusive
by any means, here are some of the more basic terms you might come across, and their definitions.
Breeding and Mating:
FLOCK MATING. In the world of poultry, flock mating is simply allowing a flock of hens and roosters to breed freely. Eggs from the flock are incubated, either naturally or in an incubator, as a means of generating new offspring. This is the method used to generate larger volumes of new offspring. In flock mating, fowl not meeting ideal standards are often removed, or culled, from the flock, in order to maintain high quality and set standards within the flock.
LINE BREEDING. Line breeding is the controlled process of breeding closely-related animals — within a family or line to concentrate desired
traits within the group. It may mean that females are bred back to their
father or grandfather, or that halfsiblings are mated together. Because of
the inbreeding involved, there is also the potential to bring out undesirable
traits. Line breeding requires a willingness and ability to cull and remove any birds from the breeding program that do not meet standards or have less-than-desirable traits. In line breeding programs, detailed histories are kept, showing which birds or animals were mated together and details of the flock lineage. Line breeding is common in cattle, sheep, and poultry improvement plans.
Genetic Terminology:
ALLELE. Allele technically refers to a gene that is part of a pair of genes, at the same locus on a pair of chromosomes. Sometimes you may see the word allele substituted for the word gene.
AUTOSOME. Any chromosome other than a sex chromosome.
CHROMOSOMES. These are segments of DNA (short for deoxyribonucleic acid). These are found within the nucleus, or center, of a cell. The “genes” are attached to these. The chromosomes are in pairs in all cells, except the sex cells (egg cells and sperm). Sex cells only contain one-half of each set, or
pair. Thus, when an egg and sperm join together, the new, developing
organism will have received one-half of its chromosomes from the mother,
and one-half of its chromosomes from the father. The term, chromosome,
literally means “colored body,” since these show up under a microscope,
after a preparatory staining or coloring.
Each species of animal or plant has its own number of chromosomes in its cell nucleus. Chickens have 39 pairs or 78 individual chromosomes in each
cell.
DILUTE/DILUTION. In the world of genetics, there are colors and patterns that may be altered or less pronounced because of one or more genes within the genome. These are often known as “dilution genes.” One example of this is lavender or “self-blue” plumage in chickens. Two recessive, autosomal genes are present in the bird’s genetic makeup, which dilute or alter both black and brown or red pigments in the feathers, causing them to have a lavender or “blue” color (actually it is a shade of light gray). Two self-blue birds, when bred together, will produce all self-blue offspring. In actuality, there are at least two other known sets of
modifying or helper genes that work in conjunction with the self-blue
genes to make this happen.
Sometimes you may hear the term “dilute barring.” In this case, it means that only one sex-linked barring gene is present. The barred pattern will still be there, but it may be less distinct and clear. Hence, the term “dilute.”
DOMINANT GENE. A gene that, by itself, will cause an organism to have
a certain trait. In nomenclature or writing about genetics, they are always
designated with a capital letter.
GAMETE. A reproductive cell. Can be either an egg or a sperm.
GENES. These are actually just shorter segments of DNA that are attached to, and lined up, along the edges of the chromosomes. The genes hold the blueprint or “code” that designates what the animal or plant will look like and what traits it will have.
GENOME. The whole big picture of all the genes and chromosomes put together, in an animal or plant.
GENOMICS. The study of genetics at a cellular and molecular level.
GENOTYPE. This refers to the actual genetic makeup in an organism’s cells. So far there have been over 23,000 genes identified in the lowly little chicken.
GERM CELL. Same as a gamete.
HETEROGAMETIC. This refers to differing sex chromosomes carried by an organism. For example, in chickens, the female is heterogametic. She has
both a Z (“male” sex chromosome) and a W (“female” sex chromosome) in her genome, or genetic makeup.
HETEROZYGOUS. This means that only one of the genes for a particular trait is carried by the animal or plant.
hom*oGAMETIC. This means that the organism carries two of the same
sexual chromosomes. In chickens, males are hom*ogametic, as they carry two Z chromosomes in their genome.
hom*oZYGOUS. Two genes for the same trait, carried by the animal or plant.
LETHAL GENE. These are genes that, when two genes are present (in a
hom*ozygous state), usually cause the organism to die during development,
or shortly after hatching or birth. These genes are usually recessive.
LOCUS (PLURAL: LOCI). This is simply the “location” of where a gene sits on a chromosome.
MODIFYING, OR “HELPER” GENES. These are genes that, in some way, modify or change the effects of other genes. In reality, many genes work on each other, to a certain extent, as modifiers.
MUTATION. A change in the actual molecular structure of a gene. These
changes can be either good or bad. Such a mutation may then make a physical change in the actual structure of the new organism.
PHENOTYPE. This refers to what the animal or plant actually looks like.
RECESSIVE GENE. Always designated by small letters in nomenclature, these genes require two of them, working together, to give an organism a certain trait.
SEX CHROMOSOMES. The chromosomes that determine an organism’s sex. In birds, these chromosomes are called Z and W. Males have two Z chromosomes; females have one Z and one W chromosome.
SEX-LINKED GENE. A gene attached to either the Z or the W sex chromosome. In birds, most sex-linked traits are due to a gene on the male, or Z chromosome. One example is the dominant gene for black and white
barring on the feathers, which is carried on the Z, in fowl. Breeding and genetics are fascinating because of the unending variations that so often show up in any breeding project. The sky is the limit, and the possibilities are endless. What hidden genetic secrets can you find out about your birds?
DOUG OTTINGER lives, works, and writes from his small hobby farm in Northwest Minnesota. Doug’s educational background is in agriculture
with an emphasis in poultry and avian science.
Originally published in the February/March 2023 issue of Backyard Poultry magazine, and regularly vetted for accuracy.
