![]() If the X chromosome carrying the gene for orange fur is inactivated, that cell will create black fur. Because the Xs that are inactivated are chosen at random, the pattern on each calico cat is distinct from another. In a calico cat, the gene that dictates fur color happens to be located on the X chromosome.Īs shown on the illustration below, if the X chromosome carrying the gene for black fur gets inactivated, that cell will instead create orange fur. ![]() The RNA molecules initiate other changes that lead to the X chromosome being condensed down into a small, dense, cluster of DNA (seen on the image below.) The inactivated X is now called a "Barr Body" named after Murray Barr, the person who first discovered the structure.īut, what does this have to do with a calico cat? It is inactivated through a process that slathers the chromosome with small RNA molecules, resulting in those genes not being expressed. ![]() Humans have the opposite strategy. Females shut down one of their Xs early on in the process of embryogenesis (when the fertilized egg (zygote) divides to form the cells that will eventually become a person) through a process called "X chromosome inactivation." The X that is inactivated is chosen randomly in each cell. For example, male fruit flies express the one copy of their X twice as much as female fruit flies, making up the difference that way. There are different compensatory solutions to this predicament, which is species-dependant. So, they need to compensate somehow for this imbalance. One complication is that, males only have one X chromosome (XY) and females have two (XX.) However, females cannot survive if they have double the proteins made by the X chromosome. Therefore, the X chromosome is required for all humans, not just females. It is large and has hundreds of genes on it, many of which are essential for cells to survive. SRY makes a protein that works to create male traits, for example, controlling the production of male hormones among other male-related things. One of the genes on the Y chromosome is called the SRY (sex determining region Y) gene. The Y chromosome is important in the process of becoming male. This is clearly illustrated by all females, who obviously do just fine without any Y chromosomes. The Y chromosome has very few genes on it (only 72 that make proteins) and none of those genes is required for the cell to survive. This is not the case for all animals, but, that is a topic for another article. And, since the sperm that fertilizes the egg also determines the sex, if a sperm carrying a Y wins the race, you are male. In most cases, there is an equal chance for either type of sperm to make it to the egg, which always has an X chromosome. Whether a cat (or human) is biologically male or female is dictated by which sex chromosome (X or Y) they got from their father's sperm. (1) A male cat with an XY could not make this same pattern of fur. You see, almost all calico cats are female which means that they have two X chromosomes in every cell. The black and orange patches that define the coloring of a calico cat beautifully illustrate the genetic mechanism known as "dosage compensation." Not just any cat - it has to be a calico, specifically. In order to appreciate the power of genetics, you only need to take a good look at a cat.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |