![]() Technically, if you are a girl it is an actual pair (XX), but if you are a boy, they are different (XY). Humans have 23 homologous pairs of chromosomes: 22 pairs of autosomes and 1 "pair" of sex chromosomes. They carry the same type of information (that is, the various genes on that chromosome), but they are not identical because each will have slightly different DNA sequences by which you can tell them apart. These two chromosomes, one from each parent, are known as homologous chromosomes (or a homologous pair). These two copies are not exactly the same, though one is from Mom and one is from Dad. To recap, a diploid cell has two copies of each type of chromosome. ![]() Now we've mentioned that a haploid cell has n chromosomes, while a diploid cell has 2n chromosomes. Cytogenetics is the study of karyotypes and is a important tool when studying human chromosomal abnormalities and diagnostically in prenatal screening. Although, it takes a lot more coiling of the DNA and histones to produce this shape, which first appears during prophase.Įvery eukaryotic organism has its own particular number of chromosomes of a particular shape and size. Together, the DNA and proteins are known as chromatin, which translates roughly as "colored stuff" in fact, the word chromosome literally means "colored body."ĭuring S phase, that DNA molecule is replicated to form the beginnings of what most people think of as a chromosome – a cross-shaped structure, pinched in at (or near) the middle. And by naked, we mean doesn't have any histones. ![]() Except in bacteria-their DNA is completely naked. But, a chromosome isn't DNA it also contains proteins, called histones, which the DNA is wrapped around for protection and support. Most of the time, each chromosome is a single, long molecule of DNA. Now let's step back and talk briefly about chromosomes. In other words a diploid cell that has 2n chromosomes produces four cells, each of which contains n chromosomes. In meiosis, however, you start with a diploid cell that divides twice to produce four haploid cells. If a haploid cell undergoes mitosis, which is something certain types of plant and fungus do as part of their normal life cycles, the end result is two identical haploid cells (n→n). Prokaryotic cells, for example bacteria, use this process to reproduce asexually, in a process known as binary fission. Therefore, if a diploid cell undergoes mitosis, the result is two identical diploid cells (2n →2n). ![]() This makes a lot of sense, because mitosis is essentially like making a photocopy: it creates a perfect reproduction of what you started with. If a haploid cell has n chromosomes, a diploid cell has 2n (n represents a number, which is different for every species – in humans, for example, n = 23 and 2n = 46).īoth diploid and haploid cells can undergo mitosis. Diploid cells comprise the majority of your body, while examples of haploid cells are eggs and sperm. This is in contrast to a haploid cell, which only has one copy of every chromosome. A diploid cell has two of each chromosome, one from each parent. In order to understand these two processes, it is important to become familiar with the terms diploid and haploid. We will go through all the detailed steps of mitosis and meiosis in the next section, but first let's focus on how the processes have some features in common, yet are still different. We have mentioned two types of nuclear division: mitosis, where the nucleus divides into two identical nuclei, and meiosis, which results in the production of four nuclei with half the original number of chromosomes of the parent cell.
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