A basic understanding of genetic inheritance is helpful for a breeder to work towards bettering the breed. Through a carefully thought-out program of test breeding, inbreeding, and selective breeding your chance of achieving the goal of a well-bred rat are greatly improved.
Rats have 42 chromosomes in each cell with the exception of the sex (germ) cells which have 21. Each offspring inherits the chromosomes from the parents via the egg and the sperm cells.
The arrangement and the makeup of the genes on each of these inherited cells combined with its match will determine the genetic makeup of each baby.
Since there are usually different combinations of genes in each of the sex cells, the offspring will have varied genetic makeup. The exception to this would be heavily inbred lab lines where the rats are almost genetically identical.
In this section of the Breeding Guide we will touch on such things as the genes that affect appearance and type, genetic mutations, and genetic diseases.