Allele: Genes come in pairs (one from the father, one from the mother). An allele is either of the two paired genes affecting an inherited trait
Carrier: An animal having a recessive gene in its genetic make-up. A black animal that has a hidden recessive Dun gene, could be termed a carrier of dun. Sometimes the term carrier is used in co-dominant traits.
Chromosomes: The cell material which acts as the means for transporting genes during cell division.
Codominant: an allele that causes the heterozygous form to appear like an intermediate between the homozygous recessive and the homozygous dominant form. (All three look different from each other.) Example: Short-legged, (heterozygous form) is the intermediate between the Long-legged (homozygous recessive), and Bulldog (homozygous dominant). It may be important to note that recessive, dominant, and co-dominant are clinical terms, i.e. they are based on the outward appearance of the animal.
Dominant: an allele that causes the homozygous dominant form and the heterozygous form to look the same as each other. Example: You cannot tell a homozygous polled or a heterozygous polled animal apart. They are both polled.
Gametes: Sperm and eggs.
Genes: The units or factors of heredity that are responsible for the expression of any characteristic. Genes are tiny segments of protein contained in all cells. They normally occur in pairs and form the bridge of inheritance from one generation to the next.
Genotype: The genetic make-up of an animal. Compare to Phenotype.
Recessive: an allele that affects an animal's appearance only if it's present in the homozygous state. Example: A black animal that is heterozygous for red is still black. The animal has to have two red alleles to appear red. Black is dominant, red is recessive.
Heterozygous: having two different alleles for a genetic trait.
Inbreeding: Practice of mating animals more closely related than the average of the population. Examples: full brother to sister, sire to daughter, or son to dam.
Homozygous: having identical alleles for a genetic trait.
Lethal Gene: A gene which causes the death of the calf, usually before or at birth. Most gene pairs causing inherited lethals must be in the homozygous (pure) condition to be fatal to the calf. By this definition the gene that causes the short-legged Dexter is a lethal gene, but in itís heterozygous form Ė therefore not in itís fatal form.
Mutation: A rare change in the DNA.
Phenotype: The way the animal appears. Example: An animal that is phenotypically Red may have a genotype that includes hidden Dun genes.
Probability: The likelihood, chance or odds of the occurrence of any particular event. The odds of getting a heifer are 50:50 or 1:1.