Principles of Genetics and Breeding

6.1.2.1. Mutations caused by changes to ploidy level

Changes in the number of chromosomes can also cause mutation.

Aneuploidy: Gain/loss of individual chromosome, from a set. There are several reports of aneuploids in salmonids. E.g., a male brooktrout that was trisomic for a chromosome carrying a LDH-B enzyme locus was reported. This fish was fertile and produced euploid and trisomic offspring in equal frequencies; the trisomics were similar in size, appearance, and viability to the normal fish. “A few” trisomic and monosomic rainbow trout were also reported. These aneuploids also had no obvious differences from normal fish. Thus aneuploid salmonids seem to be common and viable.

1.Nullisomics (2n-2)	-	both of a pair of homologous missing from a diploid set
2. Monosomics (2n-1)	-	one chromosome from a diploid set missing.
3.Trisomics (2n+1)	-	one extra chromosome.