Freemartin-- Female born twin to a bull calf (approximately 9 out of 10 will not conceive).

Generation interval--Average age of the parents when the offspring destined to replace them are born. A generation represents the average rate of turnover of a herd.

 Genes--The basic units of heredity that occur in pairs and have their effect in pairs in the individual, but which are transmitted singly (one or the other gene at random of each pair) from each parent to offspring.

Genetic correlations--Correlations between two traits that arise because some of the same genes affect both traits. When two traits (i.e., weaning and yearling weight) are positively and highly correlated to one another successful selection for one trait will result in an increase in the other trait. When two traits are negatively and highly correlated (i.e., birth weight and calving ease) to one another, successful selection for one trait will result in a decrease in the other trait.

Genotype--Actual genetic makeup (constitution) of an individual determined by its genes or germplasm. For example, there are two genotypes for the polled phenotype [PP (homozygous dominant) and Pp (heterozygote)].

Genotype-environment interaction--Variation in the relative performance of different genotypes from one environment to another. For example, the "best" cattle (genotypes) for one environment may not be the "best" for another environment.

Gonad--The organ that produces the reproductive cells, the testicle in the male and the ovaries in the female.

Half-sibs--Individuals having the same sire or dam. Half-brothers and/or half-sisters.

Heat synchronization--Causing a group of cows or heifers to exhibit heat together at one time by artificial manipulation of the estrous cycle.

Heifer--A female of the cattle species less than three years of age that has not borne a calf.

Heredity--The transmission of genetic or physical traits of parents to their offspring.

Heritability--The proportion of the differences among cattle, measured or observed, that is transmitted to the offspring. Heritability varies from zero to one. The higher the heritability of a trait, the more accurately does the individual performance predict breeding value and the more rapid should be the response due to selection for that trait.

Heritability estimate--An estimate of the proportion of the total phenotypic variation between individuals for a certain trait that is due to heredity. More specifically, hereditary variation due to additive gene action.