22,000 Genes for Cattle
The genome is all the genes for a cell, and therefore for an individual. The gene corresponds to a sequence, a region of the DNA, located in a very specific place (locus) on a chromosome, which can be assimilated into all the hereditary material of an individual. Each region of DNA which produces a molecule of functional RNA is a gene.
More precisely a gene is a unit of genetic information, or of heredity, controlling a particular characteristic. Genes are transmitted from generation to generation and they occupy a specific place on a given chromosome (its locus) with, on average, 3000 other genes. So the same gene will always be located on the same locus for all the individuals in the same breed.
The genotype is the information carried by the genome of an organism and it is contained in each cell of this organism. The genes of a living being are normally found in all the members of its species. However, there are several versions of each gene. The different versions of a single gene are known as alleles. This gives a significant number of different combination possibilities between the genes.
Each genotype is therefore usually unique except in exceptional cases like identical twins. Genotype is often familiarly known as the “genetic identity card” of an organism.
Genotyping is aimed at determining the identity of a genetic variation, at a specific position on all or part of the genome. As for sequencing this is aimed at determining a sequence, i.e. a certain portion of DNA, accurately. The procedure used makes it possible to determine the order (sequence) of bases making up a fragment of DNA.
Cattle possess 30 pairs of chromosomes and 22,000 genes (nearly 15,000 of which are equivalent in seven other species of mammals).