Syrian Hamster Genetics:  Mutation

Mutation Basics

Every time a cell divides each chromosome is replicated (copied exactly) so that the daughter cells will have the same chromosomal complement as the original.  Rarely, a mistake is made during replication that alters (mutates) a gene, producing a new allelic form.  Radiation and certain chemicals can also induce mutations.  Once a mutation occurs it is permanent and will be copied faithfully with cell division.  Mutations in germ cells (cells that become eggs and sperm) can be passed on to future generations.

Most mutations are harmful.  Embryos from mutated germ cells are often incapable of survival.  A seemingly innocuous mutation like a change in fur color may make an animal in the wild much more visible to predators.  Its genes would not be passed on, and the mutated gene would become extinct.  This keeps the animals of a species looking very similar, and this look is called the wild type.  The color and markings of a wild type are also referred to as agouti.

The Agouti phenotype in the Syrian hamster is the common shorthair Golden.  It has a golden brown coat with a dark slate grey undercolor.  The coat is ticked through with black guard hairs.  There is a golden brown chest band and black cheekflashes in front of ivory crescents.  The belly is also ivory.  Eyes are black.  Ears are dark grey.  The Golden hamster has an agouti phenotype at every locus governing color, coat type and pattern.

Once animals are captured and bred in captivity, mutations are watched for, and if they cause what is felt to be a desirable change, they are selected for.  In this way, over time, many different phenotypes can be developed.

Mutation in Syrians

Syrian hamsters have 44 chromosomes - 21 pairs of autosomes and 2 sex chromosomes.  On these chromosomes are tens of thousands of genes, all governing the hamster's appearance and functioning.  Of these, only about two dozen have been identified that affect color, coat type and pattern.  Several are restricted to laboratory populations, leaving 21 that are seen in pet and show stock.  Some are very common; others may be extinct or nearly so.  Each of these genes has become identifiable only because a mutation has occurred at the locus.

The following table lists the mutations along with the possible genotypes for each locus.  In a wild population, genotypes would hardly ever include mutant genes.  (For example, at the E locus, an agouti hamster would nearly always be EE, not Ee which would have required either a mutation or inheritance from a parent with e.)  In human-owned stock, agouti hamsters often carry hidden recessive mutant genes.

Table of Mutations

A few things to note:

All wild type counterparts to the recessive mutations are considered to be completely dominant.  That is, there is no reliable difference in phenotype between AA and Aa, EE and Ee, etc.  It is appreciated by show breeders, however, that heterozygosity can produce subtle changes in color and coat.

The recessive mutation at the C locus in some other species is c (without any superscript).  Only the cc genotype results in true albinism.  The related mutations seen in Syrians (written with the d or e superscripts to designate them as different alleles from c) allow partial pigmentation.  Since these hamsters are not totally devoid of pigment, they are not true albinos.

For full descriptions and photos of the colors, patterns and coat types, please refer to the Pet Web Site.