![]() Without such packaging, DNA molecules would be too long to fit inside cells!įor example, if all of the DNA molecules in a single human cell were unwound from their histones and placed end-to-end, they would stretch 6 feet. The unique structure of chromosomes keeps DNA tightly wound around spool-like proteins, called histones. ![]() read more ) are often unaffected physically and mentally. Donnai and Read 1 illustrate this nicely: if you were to enlarge an average 10m cell to the size of a lecture room 10m across, then the DNA would be like a piece of string 2000km long. Chromosomes are structures within cells that contain DNA and many genes. It is estimated that each human cell contains about 2m of DNA. The human X chromosome is about three times larger than the human Y chromosome, containing about 900 genes, while the Y chromosome has about 55 genes. Chromosomes are a method of organising the DNA into manageable units. However, there are exceptions to these rules.Ĭhromosomes are also different sizes. ![]() Typically, biologically female individuals have two X chromosomes (XX) while those who are biologically male have one X and one Y chromosome (XY). In humans, the twenty-third pair is the sex chromosomes, while the first 22 pairs are called autosomes. As discussed above, each chromosome is made up of protein and DNA (a single molecule). Chromosomes seem to be thread-like in appearance and are located inside the nucleus of an animal and plant cells. A fruit fly, for example, has four pairs of chromosomes, while a rice plant has 12 and a dog, 39. A chromosome can be defined as an entire chain of DNA and it comes along with a group of stabilizing proteins. In fact, each species of plants and animals has a set number of chromosomes. Humans, along with other animals and plants, have linear chromosomes Most bacteria have one or two circular chromosomes. For example, your sex chromosomes may determine: the hormones your body. In most chromosomes, the very long thin DNA fibers are coated with nucleosome forming packaging proteins in eukaryotic cells the most important of these proteins are the histones. Chromosomes vary in number and shape among living organisms. Sex chromosomes typically determine the development of your reproductive organs and your secondary sex characteristics. A chromosome is a package of DNA with part or all of the genetic material of an organism.
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