By Doug Ottinger
UNDERSTANDING basic genetic and genetic terms is not extremely difficult. However, if it’s not something you use every day, hearing or reading a word or phrase can cause a person to scratch their head and say, “Huh? In the world of poultry farming, you may hear some basic terms in genetics and breeding. Although not all inclusive
by all means, here are some of the more basic terms you might come across, and their definitions.
Reproduction and mating:
HERD MATING. In the world of poultry, herd mating simply allows a flock of hens and roosters to breed freely. The flock’s eggs are incubated, either naturally or in an incubator, to generate new offspring. This is the method used to generate larger volumes of new offspring. During flock mating, birds that do not meet ideal standards are often removed or culled from the flock, in order to maintain high quality and set standards within the flock.
BREEDING ONLINE. Line breeding is the controlled process of breeding closely related animals – within a family or line to focus
characteristics within the group. This may mean that the females are mated to their
father or grandfather, or half-siblings are mated. Due to
inbreeding involved, there is also the potential to bring out undesirables
features. Line breeding requires a willingness and ability to cull and remove from the breeding program any birds that do not meet standards or have less than desirable characteristics. In online breeding programs, detailed histories are kept showing which birds or animals were bred and details of the lineage of the flock. Line breeding is common in cattle, sheep and poultry improvement schemes.
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 replaced by the word gene.
AUTOSOME. Any chromosome other than a sex chromosome.
CHROMOSOMES. They are segments of DNA (short for deoxyribonucleic acid). These are found in the nucleus, or center, of a cell. The “genes” are attached to these. Chromosomes are in pairs in all cells except sex cells (eggs and sperm). The sex cells contain only half of each set, or
pair. Thus, when an egg and a sperm come together, the new
the organism will have received half of its chromosomes from the mother,
and half of his chromosomes from the father. The term, chromosome,
literally means “colored body”, as these appear under the microscope,
after staining or preparatory staining.
Each animal or plant species 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 can be altered or less pronounced due to one or more genes in the genome. These are often referred to as “dilution genes”. An example of this is the lavender or “self-blue” plumage in chickens. Two autosomal recessive genes are present in the genetic makeup of the bird, which dilute or alter the black and brown or red pigments in the feathers, giving them a lavender or “blue” color (in fact, it’s a shade of gray clear). Two auto-blue birds, when mated, will all produce auto-blue offspring. In fact, there are at least two other known sets of
modifier or helper genes that work in conjunction with self-blue
genes for this to happen.
Sometimes you may hear the term “dilute the ban”. In this case, it means that only one sex-linked prohibition 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 which, by itself, will cause an organism to have
a certain trait. In nomenclature or writings on genetics, they are always
denoted by a capital letter.
GAMETE. A reproductive cell. It can be an egg or a sperm.
GENOA. They are actually just shorter stretches of DNA that are attached and lined up along the edges of the chromosomes. Genes hold the blueprint or “code” that designates what the animal or plant will look like and what traits it will have.
GENOME. The overview of all the genes and chromosomes together, in an animal or a plant.
GENOMICS. The study of genetics at the cellular and molecular level.
GENOTYPE. It is the actual genetic makeup of an organism’s cells. So far, more than 23,000 genes have been identified in the humble little chicken.
GERM CELLS. Same as a gamete.
HETEROGAMETIC. These are different 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 its genome, or genetic makeup.
HETEROZYGOUS. This means that only one of the genes for a particular trait is carried by the animal or plant.
HOMOGAMETIC. This means that the body carries two of the same
sex chromosomes. In chickens, males are homogametic, as they carry two Z chromosomes in their genome.
HOMOZYGOTE. Two genes for the same trait, carried by the animal or the plant.
DEADLY GENE. These are genes which, when two genes are present (in one
homozygous state), generally cause the death of the organism during development,
or shortly after hatching or birth. These genes are usually recessive.
LOCUS (PLURAL: LOCI). It is simply the “location” where a gene is located on a chromosome.
MODIFIER OR “HELP” GENES. These are genes that in some way modify or change the effects of other genes. In fact, many genes interact to some extent as modifiers.
MUTATION. Altering the actual molecular structure of a gene. These
changes can be good or bad. Such a mutation can then bring about a physical change in the actual structure of the new organism.
PHENOTYPE. It refers to the actual appearance of the animal or plant.
RECESSIVE GENE. Always referred to as lowercase letters in nomenclature, these genes require two of them, working together, to give an organism a certain trait.
SEX CHROMOSOMES. The chromosomes that determine the sex of an organism. In birds, these chromosomes are called Z and W. Males have two Z chromosomes; females have a Z chromosome and a W chromosome.
SEX-LINKED GENE. Gene attached to the Z or W sex chromosome. In birds, most sex-linked traits are due to a gene on the male, or Z chromosome. An example is the dominant gene for black and white
except on the feathers, which is carried on the Z, in poultry. Breeding and genetics are fascinating because of the endless variations that appear so often in any breeding project. The sky is the limit and the possibilities are endless. What hidden genetic secrets can you uncover about your birds?
DOUG OTTINGER lives, works and writes from his small hobby farm in northwest Minnesota. Doug’s background is in agriculture
with a focus on poultry and avian science.