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Why do most people have 23 pairs of chromosomes?



You may have heard that 137 is the magic number, but if you ask a geneticist, they will tell you the real magic is in 46. Why 46? Because it is the total number of chromosomes found in almost every human cell – 23 pairs to be precise – and the small thread-like structures pack all the information about who you are and what makes you unique.

DNA and chromosomes

To understand what chromosomes are, first understand what DNA is. Formally known as deoxyribonucleic acid, DNA is a complex molecule found in all plants and animals. It is found in almost every cell of an organism's body and contains all the information needed to keep the organism up and running (and develop and reproduce). DNA is also the primary way in which organisms pass on hereditary information. In the reproduction process, part of the DNA is sent from mother to offspring. In short, DNA is what tells the story of your unique biology.

As you can imagine, DNA has to be quite a long time to keep such important information. And that is ̵

1; if you stretched the DNA in a single cell all the way to its full length, it would be approx. 6.5 feet long, and if you put the DNA together in all your cells, you would have a chain about twice the diameter of the solar system.

Fortunately, the cells are clever and have an ingenious way of packing all that information into space-saving packages. Enter: the chromosome.

With its name rooted in the Greek words for color (chroma) and body (soma), the chromosome is a cell structure (or body) that scientists can see under a microscope by staining it with colored dyes (get it?). Each chromosome consists of protein and – you guessed it – DNA.

Each chromosome contains exactly one molecule of DNA, to be precise, and the long strand of genetic information is tightly wrapped around the protein (called a histone) which acts as a coil that effectively bundles the long, info-rich molecule in the perfect size and shape to fit into a cell. Each human cell has 23 pairs of chromosomes totaling 46 (except for sperm and egg cells, each containing only only 23 chromosomes.

Why 23 Pairs?

Why 23 Pairs?] It Magic numbers of 46 (23 pairs) per cell are not universal among living things. First, however, humans appear to be a "diploid" species, meaning that most of our chromosomes come in matched sets called homologous pairs ( The two members of each pair are called homologues.) Many animals and plants are diploid, but not all have a total number of 46. Mosquitoes, for example, have a diploid chromosome number of six, frogs have 26 and shrimp have a huge 508 chromosomes! 19659005] But why do people have 23 pairs? It happened during evolution. "People have 23 pairs of chromosomes, while all other large monkeys (chimpanzees, bonobos, gorillas and orangutans) have 24 pairs of chromosomes," says Belen Hurle, Ph.D. via e-mail Hurle is a researcher at the National Human Genome Travel arch Institute at the National Institutes of Health. "This is because in the human evolutionary line, two ancestral monkey chromosomes merged with their telomeres [tips] which produced human chromosome 2. Thus, humans have fewer pairs of chromosomes, which is one of the major differences between the human genome and the genome of our closest relatives. "

Let us now go back to the sperm and egg problem – these cells have only one homologous chromosome from each pair and are considered" haploid ". Here's why: When a sperm and egg seal combines their genetic material to form a complete, diploid set of chromosomes. And if you think about it, it makes perfect sense. This means that each parent contributes to a homolog of a homologous pair of chromosomes in their child's cells.

Consider blood type as a clear example: People with AB blood type inherited two different gene variations on their two homologous chromosomes – one for A and one for B – which together produced AB.

Too many or too few chromosomes

Now you know that a healthy human's textbook has 23 pairs of chromosomes in almost every cell in their body, but life is not & # 39; t always a textbook. What happens if something causes more or less chromosomes to develop? A benefit or loss of chromosomes from standard 46 (called aneuploidy) occurs either during the formation of reproductive cells (sperm and eggs), in early fetal development or in any other cell in the body after birth.

One of the more common forms of aneuploidy is "trisomy", which is the presence of an extra chromosome in the cells. A well-known result of trisomy is Down's syndrome, which is a condition caused by three copies of chromosome 21 in each cell. This extra chromosome leads to a total of 47 chromosomes per day. Cell instead of 46.

The loss of a chromosome in a cell is called "monosomy" and describes a condition in which humans have only one copy of a specific chromosome per cell. cell in contrast to two. Turner's syndrome, where women only have one copy of the X chromosome. Cell versus the common two are considered a form of monosomy.

There are also other variations of aneuploidy, and in extreme cases they can compromise a person's life. In addition, cancer cells also have changes in their number of chromosomes. In contrast to the variations that occur in reproductive cells, these changes occur in other cells in the body so that they are not inherited.


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