Click Image to Enlarge. The usual number of chromosomes inside every cell of your body is 46 total chromosomes, or 23 pairs. You inherit half of your chromosomes from your biological mother, and the other half from your biological father. Now you know the textbook example of a healthy human has 23 pairs of chromosomes in almost every cell of their body, but life isn't always a textbook.
What happens if something causes more or less chromosomes to develop? A gain or loss of chromosomes from the standard 46 called aneuploidy occurs either during the formation of reproductive cells sperm and egg , in early fetal development or in any other cell of 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. One well-known result of trisomy is Down 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 cell, rather than The loss of one chromosome in a cell is called "monosomy," and describes a condition in which people have just one copy of a specific chromosome per cell as opposed to two.
Turner syndrome, in which women have only one copy of the X chromosome per cell versus the regular two, is considered a form of monosomy. There are other variations of aneuploidy as well, and in extreme cases, they may compromise a person's life. Additionally, cancer cells also have alterations in their number of chromosomes. Unlike the variations that happen in reproductive cells, these changes occur in other cells of the body, so they're not inherited.
The X and Y chromosomes weren't named randomly — their shapes actually resemble the letters X and Y, respectively.
Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. These bases are also important because they code for proteins of the body. Each gene has the coding information for a protein or polypeptide, or a sequence of another type of nucleic acid called RNA ribonucleic acid.
Thus, the human genome codes for all the proteins in the body. These proteins can have different functions in the body.
For instance, some proteins such as keratin, which is found in hair and nails, are structural. Other proteins may serve as enzymes — molecules that help certain chemical reactions in the body. Yet others can play a role in passing messages from one cell to another cell signalling molecules or in protecting humans against disease e. In scientists around the world announced the results of an immense collaborative scientific effort, the final sequencing of the entire human genome — a sequence of around 3 billion base pairs.
Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique. The term chromosome comes from the Greek words for color chroma and body soma. Scientists gave this name to chromosomes because they are cell structures, or bodies, that are strongly stained by some colorful dyes used in research. The unique structure of chromosomes keeps DNA tightly wrapped around spool-like proteins, called histones.
Without such packaging, DNA molecules would be too long to fit inside cells. For 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. For an organism to grow and function properly, cells must constantly divide to produce new cells to replace old, worn-out cells. During cell division, it is essential that DNA remains intact and evenly distributed among cells.
Chromosomes are a key part of the process that ensures DNA is accurately copied and distributed in the vast majority of cell divisions. Still, mistakes do occur on rare occasions. Changes in the number or structure of chromosomes in new cells may lead to serious problems. For example, in humans, one type of leukemia and some other cancers are caused by defective chromosomes made up of joined pieces of broken chromosomes. It is also crucial that reproductive cells, such as eggs and sperm, contain the right number of chromosomes and that those chromosomes have the correct structure.
If not, the resulting offspring may fail to develop properly. For example, people with Down syndrome have three copies of chromosome 21, instead of the two copies found in other people. Chromosomes vary in number and shape among living things. Most bacteria have one or two circular chromosomes.
Humans, along with other animals and plants, have linear chromosomes that are arranged in pairs within the nucleus of the cell.
0コメント