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Yellow (Males, To_, Females ToTo)

The naturally occurring mutation which causes Yellow is sex linked. This means that it is expressed differently in males and females, and the results of matings involving Yellow animals can vary according to which parent is Yellow.

Like all mammals, Syrian hamsters have a pair of "sex chromosomes", which determine whether an animal is male or female. Female mammals have a pair of "X" chromosomes as their sex chromosomes, while males have one "X" and one "Y" chromosome. (The "Y" chromosome appears to be a "cut down" version of the "X", with part of the "X" being removed). When females make their egg cells each will contain a copy of one or the other of the pair of "X" chromosomes, while when males make sperm cells, half will contain a copy of the male's "X" chromosome, half a copy of the "Y". "X" sperm, fertilising "X" eggs, will give "XX" embryos which will grow into females, while "Y" sperm, fertilising "X" eggs, will give "XY" embryos which will grow into males.

The gene for Yellow, (To), can be found on the X chromosome, on the part of the chromosome missing in the Y. This means that, in effect, the female has two copies of this gene, (one on each of her two Xs), and the male only one, (on the X but not the Y chromosome). Another peculiarity about the Yellow gene is that it is "incompletely dominant". If a hamster has only Yellow genes it will be Yellow, if it has only "non-Yellow", (to), genes it will not be Yellow, and if it has one Yellow and one non-Yellow gene it will show both, as patches of Yellow and non-Yellow fur. This last pattern is called Tortoiseshell and is only found in female hamsters, since only they have two X chromosomes and so only they can have two different genes on them.

Guidelines for mating Yellow/ non-Yellow animals.

In all the following matings, please bear these tenets in mind;

"Male hamsters inherit one or the other of the their mother's two Yellow or non-Yellow genes, and show that colour".

"Female hamsters inherit one or the other of the their mother's two Yellow or non-Yellow genes, and show that colour. They inherit their father's Yellow or non-Yellow gene, and show that colour as well".

Examples

1. Mating a Yellow male to a Yellow female gives all Yellow males and all Yellow females.

2. Mating a Yellow male to a non-Yellow female gives all non-Yellow males and all Tortoiseshell females.

3. Mating a non-Yellow male to a Yellow female gives all Yellow males and all Tortoiseshell females.

4. Mating a non-Yellow male to a non-Yellow female gives all non-Yellow males and all non-Yellow females.

5. Mating a Yellow male to a Tortoiseshell female gives Yellow and non-Yellow males and Yellow and Tortoiseshell females, (in the expected ratio 1:1:1:1).

6. Mating a non-Yellow male to a Tortoiseshell female gives Yellow and non-Yellow males and Tortoiseshell and non-Yellow females, (in the expected ratio 1:1:1:1).

Explanation.

Matings 1 and 4 show that the Yellow gene is pure breeding and cannot be carried; if you mate two Yellow animals together you get only Yellow young, if you mate two non-Yellow ones you get only non-Yellow young.

Matings 2 and 3 show that the male young inherit their Yellow or non-Yellow colouration from their MOTHER ONLY, (on their X chromosome). The fact that the females show no difference between the two matings indicates that they inherit an X chromosome from EACH PARENT and show its effects equally.

Matings 5 and 6 demonstrate that males pass their Yellow or non-Yellow colouration on to their daughters BUT NOT THEIR SONS. In both cases it can be seen that the male young are the same for both matings, but that the females vary according to what their father is.

From matings 1 and 5 it can be seen that Yellow females can only come from mating Yellow males ot either Yellow or Tortoiseshell females. Yellow MALES, however, can be bred from Yellow or Tortoiseshell females REGARDLESS of the colour of the male they are bred to, (matings 1, 3, 5 and 6).

Yellow combines with Cinnamon to produce Honey and with Dark Grey to produce Smoke Pearl. Both these colours are sex linked, due to the action of the Yellow gene, although "non-yellow" animals, (which would be Goldens in the examples), would be Cinnamons and Dark Greys for Honey and Smoke Pearl respectively. Where there were GOLDEN Tortoiseshells in the examples there would be Cinnamon or Dark Grey Tortoiseshells, as appropriate.

Black Tortoiseshells are also known, and look very striking due to the contrast between the Black and the Yellow. The inheritance of Yellow in Black Tortoiseshells is the same as above. Yellow also combines with Black to produce "Yellow Black" or "Smoke Yellow", although the exact method of inheritance is uncertain.

There are at the moment no recognised Yellow derived or Tortoiseshell patterned animals resulting from combining Yellow with Cream, or Cream and Umbrous, (Sable). It is known, however, that some Cream and Sable animals ARE, in fact, genetically Yellow or Tortoiseshell, since, when they are "outcrossed" to Goldens, Yellows and Tortoiseshells result. (The resulting Yellows, invariably very pale, are sometimes referred to as "Ghost Yellows"). A close watch should be kept when breeding Self coloured animals, (such as Creams and Sables), to Agouti varieties, (such as Goldens), since the appearence of young with the Yellow gene at such times is often the only indication that there is "invisible" Yellow in the Self animals.

NHC Standard
YELLOW (To = male; ToTo = female)
TOP COAT Rich dusky yellow carried well down
BASE COLOUR Ivory yellow
BELLY FUR Ivory
CRESCENTS Ivory
TICKING Heavy and even black ticking overall
CHEST BAND Rich dusky yellow
CHEEK FLASHES Black - not solid but concentrated ticking
EYE COLOUR Black
EAR COLOUR Dark grey, almost black
NOTES  
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