This makes sense since RNA was thought to be the original molecule that brought about life on Earth. For a while it was thought that RNA only served this intermediate step, but new discoveries have revealed that RNA plays much more important roles than simply being an intermediate molecule. However, to get from DNA to protein, there is an intermediate step in which the DNA is turned into RNA before becoming protein (Photo above). The X chromosome randomly gets shut off early in development, during the blastocyst stage (image below). That means all the cells that come from the cell with the black allele shut off will become brown, and vice versa. When cells divide, they make two new cells that are exactly the same as the previous one. However, this X chromosome inactivation happens randomly in the beginning of development (during the blastocyst stage, shown in the image below), meaning some cells will shut off the chromosome with the black allele, and some will shut off the chromosome with the brown allele. They can either have two black versions, two brown versions, or a black and a brown version (the black and brown are necessary to make a calico cat).Īs I mentioned above, the X chromosome is shut down to equalize X chromosome DNA between males and females. This gene is located on the X chromosome and since females have two x chromosomes, they will have two versions of the coat color gene. In calico cats, there is a gene that determines what their coat color will be - brown or black. These versions can account for the differences in hair color, eye color, etc. All of these genes have different versions. Our height, hair color, eye color, what we can taste, etc. Genes are responsible for creating all of the different parts that make us, us. Our DNA is broken up into different sections called genes. This is what women and calico cats have in common: An essential, fundamental biological process!īut what about calico cat spots? Let’s quickly discuss how DNA makes us, and these calico cats, unique. This biological phenomenon is called X chromosome inactivation (XCI), and happens to essentially all female mammals. Because of the imbalance, females have evolved a biological mechanism to shut off one of their X chromosomes, and make the levels of X chromosome DNA between males and females equal. Since females have two X chromosomes and males have one, this means that the females have two times as much X chromosome DNA as males do. Males have an X and Y sex chromosome, and females have two X chromosomes. One pair of chromosomes is called the sex chromosomes.
Chromosomes also determine the biological sex of an organism. Different species have different number of chromosomes, from plants to insects to mammals. DNA can be broken up into different number of chromosomes - humans have 23 chromosomes. This compacted structure is called a chromosome and is compacted so much, that it can fit inside a microscopic cell. How does a structure that big fit into a space smaller than a microscopic cell? Our DNA is compacted into a structure that kind of looks like a ball of yarn. Why is it that calico cats are almost exclusively female? And how does this relate to woman? To answer these questions, we need to go back to one of the most fundamental concepts of biology: DNA.įun fact: DNA, when stretched out, is about 6 feet long. Calico cats are especially unique in their distinct coat pattern, and that usually only female cats are calico. Huskies have beautiful blue eyes and Siamese cats have white bodies with dark paws, tails, and ears. In the case of pets, we know that certain breeds of cats and dogs tend to have unique eye colors or coat patterns. They can be works of art, and sometimes shapes can be seen, like a cat whose fur pattern looks like it has a moustache. One of the most beautiful characteristics of animals is their diverse colors and patterns.
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