Syrian Hamster

Genetics

The Basics

Mutation

Inheritance

Probability

Principles of Breeding

Genotyping

 

The Basics

"For most of human time, our genes have been a mystery.  Only very recently has the genetic code been sequenced, with many genes located and understood.  Unfortunately, Syrian hamsters have not been one of the chosen species studied in this way.  Since their genes can't be seen directly, we have to infer what is hidden from what we can see by looking at the animal.  Even after careful observation, only a small portion of genetic information can be deduced."

Used by permission of Jan, The River Road Hamstery http://hometown.aol.com/theriverrd/genetics.htm

 

It is not too difficult to understand the genetics, but it is necessary to realize that everything relates to everything. So I will start from very beginning and I will try to little simplify all. For breeder, it is necessary to know the basics of genetics for deciding of breeding to avoid mistakes and errors.

So Syrian Hamster consists from various parts - organums, bones etc., which are all composed from cells. Cell is the basic building unit of organisms. It consists from nucleus, nucleolus, nuclear membrane, endoplasmic reticulum, mitochondria, cytoplasm and cytoplasmatic membrane (of course among others). If we would go more deep, we will get onto macromolecular level (proteins, nucleic acids), and further to single atoms of chemical elements, protons, electrons and neutrons, till even onto level of the smallest relized parts of atoms - quarks and partons. We will be indeed the most interested in nucleus of cell, chromosomes stored inside and DNA.

Genetics is teaching of inheritance and changeability of live systems. It is quite young scholarship and promoter is Gregor Johann Mendel who was born and lived on territory of today Czech Republic (in Silesia and in Moravia), but he accounted himself to be German and his native language was German. He did hybridizing tests in plants and in 1866 he published his effort in Versuche über Pflanzenhybriden (Tests with plant hybrids) in which he described in future named Mendel's Laws. In that time his publication had no reception and it was even forgotten. Rediscovery of Mendel's work and birth of genetics as full-value science is dated on the beginning of the 20. century. Discovery of DNA - carrier of genetic information - was of course the great moment of genetics' history. DNA was first proved in 1944 by team of American Oswald T. Awery, next findings about complimentarity of base pairs were added by Erwin Chargaff and then James D. Watson and Francis H. Crick submitted structural model of double helix DNA in 1953. In 1956 there was established the number of chromosomes in human cell, in 1963 was deciphered genetic code (a way how the information coded in DNA is readed and translated into language of proteins). Discovery of modern sequencing principles enables sequencing genomes of primitive organisms (1965 - genome of yeast), with evolving technical progress was possible to sequenate more and more great genomes, which culminated by sequenation of parts of human genome in 2001 and complete sequence of human genome was made in April 2003. So we will see new discoveries in genetics daily...

In interior of cell there is a nucleus and inside of it chromosomes. Chromosomes are bowed formations whose basic structural unit are nucleosoms - it is formation made by 8 histons winded round by the DNA. Histons are small basic proteins which have high content of electrically positive amino acids (lysin and arginin). By this positive charge they create reversible complexes with DNA. We have got  five types of histons: H1, H2A, H2B, H3 and H4. Histons H2A, H2B, H3 and H4 create always in two copies octamers - nucleus of nucleosom and around it there winds round double helixed DNA. Histon H1 is present less then other histons and although it is also bound onto DNA, it is not a part of nucleosom. By spiralisation of nucleosoms are rising chromatin fibres and by next spiralisation of these fibres are rising whole chromosomes.

The molecule of DNA is a carrier of inheritable information, it is very long and if we could wind it and measure it, we will get size nearly two metres. This long molecule is formed by doublet of fibres twisted into famous double helix. It seems like crinkly tackled stair and role of tacks has chain of moleculs of sugar and phosphoric acid and imaginary "cross buntons" of ladder are made by pairs of nitrogen reactants named as bases. We have four types of bases: adenine (A), guanine (G), cytosine (C) and thymine (T), which are connected by hydrogenous bonds always only adenine with thymine (by two hydrogenous bonds) and cytosine with guanine (by three hydrogenous bonds). Different moleculs of DNA differ by succession of these base pairs and just this quartet A,C,G,T fulfils role of "letters" of genetic code, whereas important is their exact sequence. In addition relatively short sections of genetics code composed from only few thousands of litters are crucial. For example in whole human genetic information there are around 35 thousands of these short sections and they take in only about 1% of whole DNA. For these sections of DNA we use name genes. Remaining 99% of genetic information seem to be only sort of genetic "padding" but it could be only deluding semblance. Maybe we will find the most surprising discoveries just in this "needless DNA" who can play crucial role in drive of single genes. Human and animal (for example hamster) genetic information is nearly the same in size and number of genes.



 

DNA is shortcut for deoxyribonucleic acid which is macromolecule made by chains of interconnected deoxyribonucleotides. It consists from phosphate, 5-carbonaceous sugar deoxyribose and nitrogenous bases (adenine, guanine, cytosine or thymine). DNA's most important ability is replication. During replication two structurally same daughter molecules are rising from original molecule of DNA. By this way there is assured continuum of genetic informations for next generations. Crucial role during replication of DNA play enzymes (DNA polymerase). In human there are 5 types of enzymes named DNA dependent DNA polymerases. During their working they always proceed from end 5' to end 3'. To DNA polymerase  could start connecting nucleotides of new fibre of DNA, it is needed the first disturb hydrogenous bonds - ligatures between both fibres - by DNA dependent RNA polymerase. The places, where this disturbances arise, are marked as replicate beginnings. Because of polymerase activity is only in direction from 5' end to 3' end, it is only possible to do replication only by this direction on one fibre. On this fibre goes replication continually and this chain is named as lead chain. On the other chain there is more difficult situation. Replication here goes towards direction of untwisting of double helix and discontinually in smaller sections. This parts are named Okazaki fragments and whole chain is named laggard chain. This way originated fragments connects into one fibre enzyme DNA ligase. The last enzyme needed for replication is DNA primase. DNA polymerase can't start polymerization only from one nucleotide - so we have just DNA primase (which is indeed DNA dependent RNA polymerase), which synthetizes short section of RNA - primer - from which DNA polymerase can start polymerization. This primer arise not only on lead chain but also it must arise before every Okazaki fragment in laggard chain. Primers are after it cleaxed - missing sections are synthesized out and fibre is connected by DNA ligase. DNA polymerase does 1 mistake for about 107 replicated bases.

 

Mutations are changes in genotype of organism against normal. The most of mutations are random, goal-directed mutagenesises are used only for scientific purpose. In nature there is possible only keep up profitable or neutral mutations, because unthrifty mutation ends mostly by death of mutant or it makes disadvantageous conditions for survival. For example Silver Grey Syrian Hamster couldn't get off attention of predator for a long time in yellow desert and so he couldn't get its mutated genes further. In deserts and semi-deserts of Syria from where the Syrian Hamster originates, the best colouration is golden which the best unites with surround. Mutations are differenced by place and way of origin onto genic (they proceed on level of fibre of DNA - by addition, waste or compensation of bases), chromosomal (the number or structure is changed - by multiplying, waste or turnover of piece of chromosome, by line up of part of chromosome onto another chromosome or by decay of chromosome onto fragments), genomic (multiplying of the whole chromosomal pack), then mosaicism (inseparation of chromosomes it becomes once during mitosis in developing organism - on somatic level) and chimerism (individual is made by two lines of cells arose from two different zygotes which subsequently fused into one individual - for example connate twins). Frequence of creation of mutations is approximately constant in time and in allied specieses very similar.

Mutagenes are compounds which are able to evoke mutations. We can dispart them on physical (UV-radiation, RTG-radiation), chemical (aromates - nicotian smoke, dyes, organic solvents, fertilizers, herbicides) and biological (viruses).

Gene is specifically stored unit of inheritable information. From molecular aspect it is a section of nucleic acid with specific sequence of nucleotides. Every gene has got own unique place on definite chromosome. This place is named genic locus. About genes stored on the same chromosome we say that they are in genic bond. According to power of genic bond these genes are inherited either always together (strong bond) or separately (weak bond). The power of this bond is inversely proportional to distance between genes - the larger distance the weaker bond. Allele is concrete form of gene. In diploid cell for one gene always exist 2 alleles. Allele, which is commonly in population in nature, we call wild allele, unwanted allele we call mutated allele. If both alleles are the same, individual is named homozygous, if they are different we call it heterozygous. Though locus can have more alleles as well - example of this is locus C.

Interallelic relations of the same gene is whole dominance and recessivity, incomplete dominance and recessivity, codominance and superdominance. Dominant allele inhibits show of recessive allele and it is a habit to mark it by capital letter. We breeders manage purely with dominance and recessivity without marking if it is whole or incomplete and codominance. Only for your imagine whole dominance shows itself in full power already in heterozygotes (Banded Syrian Hamster), incomplete dominance even in homozygotes (Silver Grey Syrian Hamster, when heterozygote Sgsg is "less" Silver Grey then homozygote SgSg). For our definition it will be enough if we will say that dominant mutation is mutation, when only one mutated allele is enough to see changes in animals (Banded Ba_), recessive mutation will be seen only if it is present in both alleles (Black aa). Codominance is status, when both present alleles in heterozygote approves itself in whole extent and not interacts each other (heterozygote Extreme Dilute cdce). But we have yet genic interaction, when gene approves only when other gene is present also and polygenic inheritance, when to get the final effect we need many genes of weak effect (eyes colour, high).

Syrian Hamster reproduces gamic with using gametes (sperm, egg) and female is marked XX and male XY. Gametes carry half of inheritable information of new individual, so only 22 chromosomes. During fertilization individual gets whole set of 44 chromosomes, one half from father, one half from mother. Gametes rise in parents by reduction dividing - by meiosa - in practice it means that parent can give to descendant only some of its genes - from every genic pair only one (one allele). Here only marginally I need to remind rules of Mendel inheritance - 3 Mendel's rules: 1. Mendel's rule (about uniformity of F1 - the first generation of descendants from crossing two homozygotes), 2. Mendel's rule (about casual segregation of genes into gametes - during crossing of 2 heterozygotes descendant can get either from both alleles (dominant as well as recessive) with the same probability) and 3. Mendel's rule (about independent combinating of alleles).

Here I would like to end my additional interpretation of what I felt needed add to basics of genetics and next I will use excellent work of Jan, The River Road Hamstery like link to her sites with only sometimes added few photos or commentary.

 

Chromosomes and Genes - Sex Chromosomes and Sex Linkage

see Jan's site http://hometown.aol.com/theriverrd/basics.htm

 

X-Inactivation

see Jan's site http://hometown.aol.com/theriverrd/basics.htm

X-inactivation in Syrian Hamster - black areas made by X chromosome from one of parents and Yellow Black from the second parent