Gerbil Genetics ~ Section 1
For many keepers of gerbils, their coat colour genetics may not be of much interest to them or of much use, but for a breeder of gerbils it can be very useful to have a grasp of the basic genetics of the animal they have chosen to breed. This not only can save much time and tank space, and often many unwanted litters, but if you are after a certain coat colour, it will enable you to successfully predict the outcome of crosses so that your goals can be achieved with reasonable accuracy, and in a much shorter time period. It can often be a very disappointing experience for a beginning breeder if the two pretty coat colours they have just chosen to mate together go on to produces just Golden Agouti gerbils, but with a basic grasp of colour genetics this can be avoided. Saying this, breeding itself shouldn't ever be taken lightly, and breeding for coat colours should be secondary to good health and temperament. Good breeding includes good welfare and should also include the proper after care of the pups that have been produced and are now effectively in your care.
To give you a greater understanding of how genetics work, we first need to look into the cell, and at genes, chromosomes and DNA, and to explain this we need to take a closer look at how a cell works in a gerbil's body. So let's move forward and go on a cellular journey into the working of a typical cell in the gerbil's inner ear.
Now that we have explored cells and have a better understanding of chromosomes and the DNA within them, we now need to look at how a cell replicates itself, and more importantly how the mechanisms of cell division that occurs in sex cells can pass on genetic information from both parents to their offspring.
Cell division is the process by which cells multiply during the growth of tissues and organs. Cells first make an extra copy of their genetic material. One cell then splits into two new cells, each with its own set of genetic material and other cellular structures. Cell division can occur through mitosis or meiosis. In multi-cellular organisms such as humans and of course our Mongolian gerbil, it is the body (somatic) cells which undergo mitosis, while germ cells ( these are cells which are destined to become either sperm cells in males or ova in females) divide by a similar process that is known as meiosis.
This is the process of division of body cells in which each daughter cell receives the same amount of DNA as the parent cell. The cells produced here are identical to the original cell that has been divided. The chromosomes in the cells nucleus are duplicated to generate two daughter nuclei; this is then followed by a process called cytokinesis, which then divides the nuclei, cytoplasm, organelles and the cell membrane, into two separate daughter cells carrying a roughly equal share of all these cellular components.
Mitosis and cytokinesis are the defining processes of the mitotic phase of a cells life cycle. The mitotic phase itself is relatively short in the full cell cycle, and there are several other stages where a cell will grow, then duplicate its chromosomes, prepare for mitosis and then finally divide. Each phase has its own particular name and can be seen in extreme detail in the photographs in the gallery below.
Mitosis in itself is a traumatic period for a cell, and although extremely rare, this process can go wrong. Errors in mitosis can be potentially dangerous to an organism because any future replications from an error in a parent cell will then carry the same disorder. The effects from an abnormal cell can all depend on the specific nature of the error and may range from being benign to having a noticeable effect, through to cell mutations that can lead to cancer. In many instances an error in cell mitosis will cause apoptosis, which will kill the cell. "Apoptosis" is a programmed cell death and can occur for several reasons such as when the cell is damaged beyond repair, or infected with a virus, etc, and the decision for apoptosis can come from the cell itself, surrounding tissue and even from another cell that is part of the bodies immune system. In these instances apoptosis is a beneficial process, however if apoptosis cannot occur due to a mutation or a biochemical inhibition, the cell itself will continue to divide and this process can develop into a tumour.
This is a special form of cell division in which each daughter cell receives half the amount of DNA as the parent cell. Meiosis occurs during the formation of egg and sperm cells in mammals. During meiosis all the hereditary information stored in the DNA on chromosomes in a diploid germ cell undergoes DNA replication which is followed by two rounds of division, the net result being the formation of haploid cells known as gametes. These haploid cells can then fuse with other haploid cells of the opposite sex during fertilization to create a new diploid cell or zygote (a cell which is a result of fertilization) the zygote then undergoes mitotic cell division to eventually form an embryo.
A diploid cell is simply a cell that contains genetic information from both parents. In humans most cells are diploid; they carry one set of chromosomes from each parent. A haploid cell is the sex cells (ova and sperm) and refers to their chromosome content which only has one copy of each chromosome, so have only half the number of chromosomes that are found in other cells of the body.
Meiosis ensures that each zygote produced will have a unique set of genetic blueprints encoded in its DNA, and the process of meiosis and sexual reproduction ensures genetic variation.
The process of meiosis uses many of the same biochemical mechanisms that are used during mitosis, but meiosis has several unique features. The Mongolian gerbil also has a unique form of meiosis that is shared with marsupials and some insect species, and that is the sex chromosomes that pair and segregate during the meiosis of male gerbils do so without undergoing meiotic recombination. We know that meiosis is a special kind of cell division that leads to the formation of gametes, and that the number of chromosomes has to be halved in the daughter cells, and to ensure this is done properly most organisms use a strategy where during the first of the two meiotic divisions, homologous chromosomes will associate in pairs, and then undergo a reciprocal genetic interchange, which is known as meiotic recombination, and this ensures that these homologous chromosomes remain very tightly knitted until they eventually segregate. In male gerbils though there are several proteins that are reorganised to make sure that sex chromosomes are tightly knitted together until they eventually segregate, without them having to undergo meiotic recombination.
In Mongolian gerbils, germ cell loss (apoptosis) helps regulate the amount of sperm produced, which occurs mainly during meiosis. This process ensures that most often defective cells and also cells that carry DNA mutations are eliminated. Studies on male Mongolian gerbils have shown that around 30% of germ cell loss occurs during meiosis.