Do chromosomes occur in pairs and why do chromosomes exist in pairs? What are homologous chromosomes

First of all, the question "Do chromosomes appear in pairs?" is too big a question to ask, because chromosomes don't necessarily come in pairs depending on the situation.

I fainted, I have something to do in the afternoon.

In general, most organisms are diploid and contain two sets of chromosomes, so the chromosomes in somatic cells exist in pairs.

Homologous chromosomes: refers to a pair of chromosomes with the same shape and size, one from the father and one from the mother.

Your understanding of chromosomes is biased, and it doesn't mean that every pair of chromosomes corresponds to something in your body. The 23rd pair of chromosomes is a sex chromosome, which can determine sex, but not only sex, and the genes for gender-related genetic diseases such as hemophilia are also located on the 23rd pair of chromosomes (hemophilia is specifically on the X chromosome, with X recessive inheritance).

And the other chromosomes are not a pair that correspond to a certain part of the body or a certain shape. A pair of homologous chromosomes has a variety of genes responsible for a variety of different functions, most of which cannot be seen from the characterization, such as the synthesis of various enzyme systems of cellular metabolism, and it cannot be said that this pair of chromosomes corresponds to anything in the body.

In addition, many functionally related genes, or genes from the same gene family, are located on different chromosomes. Such as p53 and its upstream and downstream genes. P53 is located on chromosome 17, P73, MDM4, and ASPP1 are located on chromosome 1, P63 is located on chromosome 3, INK4a is located on chromosome 9, MDM2 is located on chromosome 12, and IASPP is located on chromosome 19.

This example is used to illustrate that there are many traits that are not determined by one pair of homologous chromosomes alone, but by many chromosomes in many cases.

In summary, a pair of homologous chromosomes will be involved in the determination of multiple traits, and a trait is often determined by genes on multiple pairs of chromosomes, so it is impossible to say which pair of chromosomes corresponds to what in the body.

Hope it helps.

I'm talking in layman's terms: chromosomes are made up of DNA, and usually there is a DNA on a chromosome. There can be many genes on a single DNA, and there are 20,000-25,000 genes on 23 pairs of chromosomes in a person.

So the average DNA has about 1000 genes. So one chromosome can control multiple traits, because there are too many and too complex, so scientists have not been able to study every gene. But for example, the gene that controls the single eyelid and double eyelid is located on chromosome 10, and there are some genes on chromosome 10 that may be related to the formation of tumors, which are related to many physical traits, and these traits are not necessarily related, not that chromosome 10 is responsible for the eyes!

So your question is too profound, wait until scientists finish working on the genome project! By the way, China is responsible for part of chromosome 3!

If you don't understand, ask me!