Article overview chromosomes
- What is a chromosome?
- Which functions do chromosomes have?
- Where are chromosomes?
- What problems can chromosomes cause?
"> What is a chromosome?
Chromosomes are the carriers of the entire genetic information of an organism and are located in the cell nuclei.
Most of the time, the chromosomes are present as a rod-like or hook-like single strand called chromatid. This is also referred to as a one-chromatid chromosome.
Shortly before a cell and nuclear division, the chromosomes must be doubled. Thus arise two identical chromatids which bind together at one point (the centromere). The two chromatids of these two chromatid chromosomes are pulled apart in the central division (mitosis) at the centromere and towards opposite cell poles. In between, a new cell membrane is formed - two new daughter cells, each with a complete set of chromosomes, have been created.
Chromosomes consist on the one hand of the DNA (abbreviation for deoxyribonucleic acid), which has stored the genetic information in the form of individual genes. On the other hand, chromosomes contain special proteins (such as histones).
In the time between successive cell divisions (interphase) chromosomes are present in a loosened form as chromatin in the cell nucleus. But as soon as a cell and nuclear division is pending, the chromatin is transferred into a more densely packed form of transport - the chromosomes.
Read more about chromatin in the article "Chromatin"
How many chromosomes does a human have?
The normal number of chromosomes (human) in all nucleated body cells (except the egg and sperm cells) is 46. Strictly speaking, there are 22 autosomal pairs and 2 sex chromosomes (gonosomes). This is called a double (diploid) set of chromosomes.
Each copy comes from the mother and father. The same applies to the two sex chromosomes: Each parent has "contributed" a gonosome during procreation (fusion of egg and sperm cell).
The oocytes and spermatozoa (spermatozoa) have a simple (haploid) chromosome set: In the formation of germ cells, the normal double chromosomal rate must first be halved (in the course of so-called reduction division or meiosis). Only in this way does the fusion of egg and sperm cell result in a cell with a double chromosome set, from which a new person then grows.To the table of contents
Which functions do chromosomes have? "> What is the function of chromosomes?
The chromosomes contain the entire genome of an organism - for example, the genetic information about hair color, height and possibly the risk of certain diseases. In each body cell, however, only the genetic information that the cell needs for its specific function is always active. The remaining genes are shut down.
The chromosomes also determine the sex of a human: The sex chromosomes in women are two X chromosomes. Men, on the other hand, have an X and a Y chromosome as a pair of gonosomes.
Read more about the gonosomes in the articles: "X-Chromosome" and "Y-Chromosome"To the table of contents
Where are chromosomes? "> Where are chromosomes?
They are in the nucleus of every cell of the organism - in humans, animals and higher plants.To the table of contents
What problems can chromosomes cause?
A chromosome aberration (anomaly) is referred to when the structure or number of chromosomes deviates from the "normal state". In the first case there is a structural, in the second a numerical aberration.
Down syndrome (trisomy 21) is a numerical aberration: there is an additional (third) chromosome 21 present. Typical signs include dwarfism, flat back of the head, round and flat face and slanting eyes. In addition, people with Down syndrome are susceptible to heart defects, malformations in the digestive tract, hearing and vision disorders and leukemia, among others. Often, however, there are also special abilities such as a pronounced musical talent.
Klinefelter syndrome is another numerical chromosome aberration. It affects the male sex: those affected have an additional X chromosome. Possible consequences: The testes are very small, the mammary glands often enlarged (gynecomastia). In addition, those affected are usually infertile.
Another chromosome aberration is the Ullrich-Turner syndrome that occurs in the female sex: one of the two X chromosomes is missing or has structural defects. This usually leads to dwarfism, malformed ovaries and infertility.
A rare part of chromosome 5 is missing in rare crying syndrome (cri-du-chat syndrome). The affected babies emit shrill, monotonous screams like a cat's. In addition, a small head, a wide root of the nose, a strikingly small jaw, and psychomotor and mental retardation are symptoms of this chromosome aberration.