Coat patterns are patterns of white (or other colours) that go "on top of" any hamster base colour.
Banded
One of the most common coat patterns is banded. Banded is on the Ba locus and is a dominant pattern (BaBa or Baba). A perfect banded pattern creates a solid white band around the middle of the hamster with two blocks of colour on each side. Oftentimes, bands aren't perfect and the white may be more irregular, or may have coloured spots inside the band. The quality of bands only matters for showing and has no effect on the health of the hamster.
One of the most common coat patterns is banded. Banded is on the Ba locus and is a dominant pattern (BaBa or Baba). A perfect banded pattern creates a solid white band around the middle of the hamster with two blocks of colour on each side. Oftentimes, bands aren't perfect and the white may be more irregular, or may have coloured spots inside the band. The quality of bands only matters for showing and has no effect on the health of the hamster.
The first picture here shows Hathor's Ara and banded baby Lingonberry. As you can see, Lingon's band is not perfect and has some spots and lines down the band. On the right, Hathor's Ursa and a few of her babies. Ursa has my favourite kind of band, a solid stripe down the back. It is certainly not a perfect band, but it sure is cute!
Dominant Spot
Dominant Spot is a white pattern that creates a spotted-like appearance on the backs of the hamster. Dominant spot is located on the Ds locus and is a dominant pattern, however it is homozygous lethal and so is only found in the genotype as Dsds and not DsDs. Dom spot hamsters have a white blaze on their face that covers the nose and goes up over the forehead. Dom spot hamsters also have a white belly.
Dominant Spot is a white pattern that creates a spotted-like appearance on the backs of the hamster. Dominant spot is located on the Ds locus and is a dominant pattern, however it is homozygous lethal and so is only found in the genotype as Dsds and not DsDs. Dom spot hamsters have a white blaze on their face that covers the nose and goes up over the forehead. Dom spot hamsters also have a white belly.
Holmden Hill Haven's Happy and Chap are both examples of dominant spot hamsters on a black and golden base colour, respectively.
Recessive Dappled
Recessive Dappled is a recessive white pattern on the Rd locus (rdrd). Recessive dappled is similar to dominant spot, however the patterns show up differently. Recessive dappled hamsters often have a blaze that comes over the top of the head and down, leaving spots of colour around the ears that vary in size. Recessive dappled hamsters often have more white on their body, and have small spots of colour on the rump with mottled ears.
Recessive Dappled is a recessive white pattern on the Rd locus (rdrd). Recessive dappled is similar to dominant spot, however the patterns show up differently. Recessive dappled hamsters often have a blaze that comes over the top of the head and down, leaving spots of colour around the ears that vary in size. Recessive dappled hamsters often have more white on their body, and have small spots of colour on the rump with mottled ears.
Hathor's Yoshi and Marvel show examples of recessive dappled on ED black tortoiseshell and cream, respectively.
Holmden Hill Haven's Skeebo and Happy show good examples of the difference between recessive dappled (left) and dominant spot (right) patterns. We can see Skeebo has a blaze that goes over the top of the head and stops before covering the nose. If we remember from before in the dom spot section, Happy has a blaze that covers the nose and goes over the jawline.
Tortoiseshell
Before reading this section on tortoiseshell, please also read the section on yellow on the basic genes page. Tortoiseshell is a sex-linked gene on the To locus. We know already that To is linked to the X chromosomes and produces yellow on a male with To (ToY) and yellow on a female with two To alleles (ToTo). When a female has only one To allele, this creates the tortoiseshell pattern (Toto). Cells on the females body will randomly activate either the To allele (producing yellow pigment) or the to allele (producing base colour pigment). The level of yellow pigment on the hamster is random and not genetic.
Before reading this section on tortoiseshell, please also read the section on yellow on the basic genes page. Tortoiseshell is a sex-linked gene on the To locus. We know already that To is linked to the X chromosomes and produces yellow on a male with To (ToY) and yellow on a female with two To alleles (ToTo). When a female has only one To allele, this creates the tortoiseshell pattern (Toto). Cells on the females body will randomly activate either the To allele (producing yellow pigment) or the to allele (producing base colour pigment). The level of yellow pigment on the hamster is random and not genetic.
Hathor's Cassava is an example of a flashy extreme dilute black tortoiseshell. SBH's Arya is an example of a classic black tortoiseshell hamster.