Genetics

Basics

DNA (deoxyribonucleic acid) is carrier of genetic information of most of organisms. There are coded all informations which are necessary for life - growing (how organism looks like) and survival. DNA is biologic large molecule in form of chain of nucleotides. Nucleotides are composed by deoxyribose sugar, phosphate group and one of four nucleic bases. Information function has nucleic bases, adenine A, cytosine C, guanine G or thymine T. Two strands of DNA are very often connected and then they create known duplex DNA. The two strands of DNA run in opposite directions to each other and in between opposite bases are created hydrogen bridges, two between adenine and thymine and three between cytosine and guanine. Parts of DNA are different by order of those connected bases and this quartet A, C, G and T has role of "letters" of the genetic code. Crucial are quite short sections at which are in locuses placed genes, which determine order of amino acids in molecules of proteins, they are such a "recipes" for creating proteins. Each gene usually contains instruction for composing one protein. Proteins affect for example, when we take colour of fur, production of eumelanine, which is responsible for black (with reduction amount grey) colour and brown (with reduction amount blond) colour or pheomelanine, which is responsible for red colour (hamster lips) and yellow colour. Simple genes can also affect biochemical reactions when melanin is created or they regulate amount of produced melanine, amount of melanocytes or their structure.

The most important ability of DNA is ability to replicate (create copies of itself). When DNA is replicated, there are created two structural absolutely same daughter molecules. By this, there is catered continuity of genetics informations in the next generations.

Genetics information in cells of eukaryot organisms is not placed in only one molecule of the DNA. Instead of that, it is divided into more parts - chromosomes. These parts of DNA create komplex with different proteins and exist in nucleus like a kind of functional unity. Collection of all the chromosomes is called caryotype.

Chromosomes ar placed in nucleus of majority of cells of organism. They exist in very similar pairs, called homologous. Characters coded in one chromosome have almost always match on sister chromosome. One pair of genes (on sister chromosomes) can be exactly the same or different. Particular form of gene is called allele and it is variation of the gene on molecular level when each allele has small difference in sequence of nucleotides of the DNA. These slight differences are created by mutations (changes) in genotype of organism. Most of mutations are entirely random. In nature, only useful or neutral mutations survive, because inconvenient mutation can cause death or some inconvenient for surviving. For example nature colour of Syrian Hamster is golden, so it can as much as possible coincide in semidesert where Syrian Hamster originates from. If there would occur mutation Black (aa), animal probably would not be able to escape from predator´s attention, so it would not have a chance to successful reproduce and spread its mutated genes. When genes are placed on the same chromosomes, they are in genetics linkage. It depends how far away are they from each other, they can only be inherited always together (if they are very close on one chromosome) or separately. Generally more far away are they, more weak is their linkage.

So locus is a place of the gene on the DNA. Different locuses are denoted by different letters (for example A, B, C and so on), dominant genes are genes which can show themself only in one inherited copy from one parent and are marked by big letters, recessive genes must be inherited from both parents and are marked by small letters. Every Syrian Hamster baby inherits half og genetics informations from the father and half from the mother. If alleles are the same from both parents, animal is homozygous in this character (for example Black aa) if they are different baby is heterozygous (for example Golden Hamster, which is carrier of black colour of fur Aa). Some locuses can have more alleles for example locus C. Interallelics affiliations of the same gene can be total dominance or partial dominance and recessivity, eventually codominance. Example of dominance is for example Umbrous Golden (U_), recessivity Black (aa), partial dominance Silver Grey (Sg_), when SgSg hamster is more silver grey than Sgsg hamster. Codominance is a stage when both present alleles have full effect and they do not affect each other.

Syrian Hamster has 44 chromosomes, 22 pairs. 21 pairs are autosomes, which have exact match and they are denoted by numbers and 1 pair of sexual chromosomes which looks different in the microscope, when one has one side much shorter and it is called by that character Y and the other looks like letter X, so it is denoted as letter X. XY individual is a male, XX a female. There are also other genes on X and Y chromosomes, not only those sexual ones. Because they are inherited on sexual chromosomes with sex, they are called sex-linked. On female chromosome X is quite big part of DNA without match on Y chromosome, so there are also many genes which don´t have their match on chromosome Y. These genes determinate on males its phenotype. There is totally different situation with females, females have alleles on both of the chromosomes X. But inheritance functionates here bit different than with autosomes. There is chosen one of X (from father or from mother) in very early development in each cell which will be active for the rest of female´s life, whereas the other X is deactivated. This process is called X-inactivation or lyonization. After that each of these original cells is dividing and creates tissue and it imparts natural tend of activation of the same X, result of this is a mosaic female with some parts of female body under control of one of the X and the other of the other X. For example with Yellow gene when one parent transmits To allele and the other to allele it leads to Tortoiseshell female (Toto).

Genetic linkage happens to the genes which are close to each other on one chromosome. After that those genes are inherited from one parent always together. If those genes are quite far away from each other on one chromosome, they are usually separated during homologous recombination of the genes. During the formation of gametes (sperm and eggs), chromosomes go through a process called homologous recombination. First the cell makes an identical copy of each chromosome, those copies are called sister chromatides, and they remain attached to one another for now. After that they are close to one another and they swap large sections of DNA. The DNA strands actually break and rejoin. After recombination, the chromosomes still have the same genes arranged in the same order, but the alleles have been rearranged. In the end, chromosomes are devided up so that each gamete gets one copy of each chromosome of alleles for those genes. Recombination increases genetic diversity. 

Mutations of Syrian Hamster

You can read informations about mutation in this order: mutation name, genetic symbol, symbol derivation, year and place when mutation occured. Genes which look alike in homozygous and heterozygous form are marked as unknown data _.

Other mutations now believed to be extinct.

Mutations which occured in laboratories and didn´t get out of there.

Inheritance

We look for the best hamsters with genes we wish to breed for. Hamster should match exhibition standards as much as possible, which are published by Czech Hamster Club or another hamster club in given country.

Hamsters should be as less as possible relative and have desire genes. More experienced breeders can also use inbreeding but they should not forget that inbreeding concentrates good but also bad genes. Backcrossing is crossing between father and daughter or mother and son, sibling crossing is crossing between brother and sister. Sibling crossing is the most dangerous. Next tool is linebreeding, which is less risky when we breed more further relatives (for example crossing between two cousins).

Dominant genes are more easy to get, because of it is enough to inherit them only from one of the parents. We can take Umbrous (U_) gene as an example. Let´s take ideal situation when we have one of the parents homozygous UU when crossing to any other hamster will results show this trait in all the babies. If we use punnett square (mathematical tool used by geneticists to predict phenotypes and their ratios in offspring) for homozygous Umbrous (UU) hamster and Dark Golden (uu) hamster (note that we don´t have to write all the genes it has, but only locus u), it will look like this:

UU x uu

Result: 100% Umbrous (Uu)

Next example we will take is heterozygous Umbrous (Uu) and Dark Golden (uu):

Uu x uu

Result: 50% Umbrous (Uu) and 50% Dark Golden (uu)

Recessive genes must be inherited from both parents. They tend to pop up even though we don´t expect them to appear. In ideal case we have both parents homozygous in given trait. We can take crossing of two Black (aa) hamsters as an example:

aa x aa

Result: 100% Black (aa)

Next example is Black (aa) and Dark Golden (AA) hamster:

aa x AA

Result: 100% Dark Golden (Aa)

You surely noticed that there was no Black hamster baby in previous example. This should change further crossing, when we use inbreeding either father x daughter or brother x sister crossing. The first variation should give us more babies with wished trait, but it is more risky, second variation less, but it is more safe. We will write down both examples. We start with father and daughter. Father is Black (aa), daughter Dark Golden (Aa):

aa x Aa

Result: 50% Dark Golden (Aa), 50% Black (aa)

In the second example both hamsters are Dark Golden (Aa):

Aa x Aa

Result: 75% Dark Golden (AA and Aa) and 25 % Black (aa)

Punnett squares for more genes start to be more complicated. More genes we have, more complicated it is to fill punnett square. For example, we will cross Chocolate (aabb) hamster and Dark Golden hamster who is Black and Rust carrier (AaBb):

aabb x AaBb

Result: 25% Dark Golden (AaBb), 25% Rust (Aabb), 25% Black (aaBb) and 25% Chocolate (aabb)

Genetics linkage is a little bit changing results, because if some genes are linked (close to each other on the same chromosome), they are almost always inherited together. Known linkage in Syrian Hamster is Banded (Ba_) and Longhaired (ll), Dark Eared White (c(d)c(d)) or Extreme Dilute (c(e)c(e)) and Cinnamon (pp) and Umbrous (U_) and Satin (Sasa). Normally hamster with two different genes produces four different gametes in the same ratio. Dark Golden, Banded hamster who is carrier of Longhaired (BabaLl) should produce 25% BaL, Bal, baL and bal. Due to genetic linkage, it is not producing all four kinds evenly. If alele Ba is on the same chromozome like alele L and on the other chromosome is ba and l, hamster will mostly produce only BaL and bal. Rarely can occur crossing over and hamster will produce also Bal and baL. It will affect results óf breeding and very rarely can be born for example Banded Longhaired (Baball) baby (when crossed with notbanded Longhaired (baball) hamster. So genetic linkage "affects" genotype ratio and changes results in benefit of genetic linkage.

Sex-linked genes are written down with marked gender. We will look at punnett square for gender inheritance as first. Male (XY) and female (XX):

XY x XX

Result: 50% females (XX) and 50% males (XY)

Now we will add sex-linked genes into the punnett square. There is only one such a gene in Syrian Hamster and that is Yellow (To_). We take Yellow male (ToY) and Dark Golden female (toto) as an example:

ToY x toto

Result: 50% Dark Golden Tortoiseshell female (Toto) and 50% Dark Golden male (toY)

In the next example, we will take Dark Golden (toY) male and Yellow (ToTo) female.

toY x ToTo

Result: 50% Dark Golden Tortoiseshell female (Toto) and 50% Yellow male (ToY)

Even though both parents had the Yellow gene, in the sons it came only from the mother, and from the father it passed only to daughters.

Epistasis (or masking) is in genetics a situation when activity of one gene masks effects of other gene. We can take Dark Eared White (c(d)c(d)) as an example, when this colour of fur masks almost all the other colours. It is because of this gene removes almost all of the pigment. You can see effect of Cinnamon gene (pp) only on ears of Dark Eared White hamster, which changes colour of ears from dark grey to pink and this combination is called Flesh Eared White (c(d)c(d)pp). Another example is Black Eyed Cream (ee), when activity of Black (aa) gene is masked by cream gene because cream gene removes all eumelanin. Cream gene also masks Yellow (To_). 

Lethality occurs in some of the genes, which should not be bred together. Is is gene Light Grey (Lglg) and Dominant Spot (Dsds). When we cross two Light Grey hamsters (Lglg x Lglg) 25% of babies die in utero or shortly after birth.

Genotyping

Syrian Hamster has many mutations of colour of fur and these can be combined in many other colours. When genotyping Syrian Hamster, we have to look at it´s phenotype (how the hamster look like). We have many of basic agouti colours, agouti hamsters have agouti markings: cheekflashes, crescents, chestband and light coloured underside (for example Dark Golden, Rust or Cinnamon), as well as some basic self colours, when hamster has the same colour of the body, except some white markings usually on the chin, white chest stripe, white on the belly and legs (Black, Black Eyed Cream, Dark Eared White).

Natural colour of Syrian Hamster is Dark Golden (++). Its genotype can be written also like a row of all already known genes: AABBbabaBsBsCCDDDgDgdsdsEEHrHrLLlglgPPRdRdRxRxsasasgsgto_tutuuuwhwh.

Cinnamon Hamster (pp) can be written similar: AABBbabaBsBsCCDDDgDgdsdsEEHrHrLLlglgppRdRdRxRxsasasgsgto_tutuuuwhwh.

To make it more easy we can write down just ++ or pp (so only changed genes). If we write the punnett square we write down also changed genes of the other hamster. So if we cross Black x Rust, we write aaBB x AAbb.

Basic colours

We have 14 basic colours of the fur (included natural Dark Golden, Dilute - which only dilutes colour and Umbrous - which adds sooty grey wash over the entire coat colour and which creates colour Sable with Black Eyed Cream gene. Standard colours are in bold face (BHA - British Hamster Association):

Colour combinations

Basic colours can be combinated and they are creating many different colours of fur, but beware of too many colours together because you can end up with unidentifiable colour. So we have many colour combinations and the most often are written down in the table and standard colour are again in bold face, two colour combinations:

Three or more colour combinations:

Patterns of fur

Syrian Hamster has couple of patterns of fur. All but one add white spots or areas. Exception is pattern Tortoiseshell, which adds yellow colour.

Lenghts of fur

Syrian Hamster has three lenghts of fur:

Types of fur

Syrian Hamster has three types of fur:

Eye colour

Natural colour of hamster eyes is black. Some genes which change colour of fur or pattern of fur can also change colour of eyes from pink to garnet. Dark Eared White hamster (c(d)c(d)) has red eyes, Cinnamon (pp) has red eyes as well, but they darken with age to garnet and they look black already in age of 2 months. Dominant Spot hamster (Dsds) can also have red eyes, Extreme Dilute hamster (c(e)c(e)), White Bellied/Roan (Whwh) has red circles in the eyes when seen in a strong light. Rust hamster (bb) can have red eyes when together with Dominant Spot (Dsds) and White Bellow/White Sprinkled (bsbs) has in combination with Dominant Spot (Dsds) also red circles in strong light, whereas it is the best seen in the dark.

Ear colour

Natural colour of ears is dark grey, Black hamsters (aa) have black ears, Rust hamsters (bb) light brown, Dilute hamsters (dd) dilute and Cinnamon (pp) pink. Russian Shadowed hamsters (p(rs)p(rs)) have ears with spots of light grey and some patterns of fur has also spotted ears (Banded (Ba_), Dominant Spot (Dsds)).

Expanding the genotype

We can get more informations about genotype of hamster, if we know its parents or if it has babies.

Parents can give us informations about dominant and as well recessive genes. If one of the parents has dominant gene and is homozygous in this trait, 100% of the babies inherit it and are heterozygous in that trait (Silver Grey hamster (SgSg) has all the babies at least heterozygous Silver Grey (Sgsg)), if parent is heterozygous in some dominant trait, its babies might have it or not (heterozygous Silver Grey (Sgsg) can give but do not have to give this trait to the baby, so it can be heterozygous Silver Grey (Sgsg) or without Silver Grey gene (sgsg)). If both parents have the same recessive gene, it is clear, that all the babies will also have the gene (if both parents are Black (aa), all babies must be Black (aa) as well), if one of the parents has some recessive gene and baby doesn´t have, it must give it to the baby as well but we can´t see it (parent is Black (aa), baby is not Black but it carries Black gene (Aa)).

Babies also give us informations about dominant and recessive genes. If some baby has some of the dominant genes, we have to search who gave it to it (baby is Banded (Baba) but none of the parents seems to have this trait, whereas we mated Dark Eared White (c(d)c(d)) male and Dark Golden (++) female, this gene had to be inherited from the father which must also be Banded (Ba_), but its colour of fur masks its pattern). With recessive genes baby discovers genotype of parents when Black baby (aa) had to have either Black parents (aa) or Dark Golden parents, which carry gene for Black colour of fur (Aa).

So it is always good to look at parents of your hamster (what they had to or could give to the baby) and as well eventually offspring of your hamster (what it had to give to its babies).

Inadvisable matings

In conclusion we will write here down what is better not to cross together and why is that.

We start with lethal genes, dominant genes which when inherited from both parents (from father and mother the same time) mean death of such a babies, what is not good either for the mother (it can have troubles whilst giving birth) nor mostly for these babies which die in utero or shortly after birth. So it is not advisable to breed two hamsters which are both Light Grey (Lglg x Lglg) or Dominant Spot (Dsds x Dsds), because LgLg and DsDs babies can be born and they all will die.

Farther it is not good to breed genes which can make serious health troubles when it is in homozygous form: crossing two hamsters with gene White Bellied/Roan (Whwh x Whwh) produce 25% of babies which are Anofthalmig White (WhWh) so they are blind and very often death as well, so they live their life in total darkness and calmness at the same time.

It is inadvisable to mate Hairless female (hrhr), who is not able to produce milk.

Farther we have aesthetical troubles with two Satin hamsters (Sasa x Sasa), when double Satin hamsters (SaSa) are quite ungainly.

It is also not good to cross too many colours of fur together, because we can end up with indistinguishable mix. Mostly too colours which are very similar, so Dark Grey (dgdg), Light Grey (Lglg) and Silver Grey (Sg_) together. Another example is Rust (bb) and Cinnamon (pp) and Black Eyed Cream (ee) x Yellow (To_).