Carrier

A carrier is an organism that carries a disease without showing any symptoms. If the disease is genetic, the carrier will be heterozygous, with a dominant, healthy allele and a reccessive allele for the disease state. In the event of two carriers mating, there is a 25% chance their offspring will be affected by the disease, 50% chance of the offspring being carriers or a 25% chance of the offspring being healthy and not a carrier^[1].

An example of this is Cystic Fibrosis, where 1 in 25 of the white population are carriers of the CF gene, showing no signs of having CF themselves.

A Punnett Square showing two carriers mating: (H is healthy, dominant allele, he is recessive for disease state) indicates how alleles from each parent cross.

	H	h
H	HH	Hh
h	Hh	hh

References

1. ↑ D.L. Hartl, E.W.Jones.(2000)Genetics: analysis of genes and genomes, 5th edition. Sudbury, Jones and Bartlett publishers