{"id":1475,"date":"2026-01-25T15:18:49","date_gmt":"2026-01-25T21:18:49","guid":{"rendered":"https:\/\/zogen.local\/?p=1475"},"modified":"2026-01-25T15:18:49","modified_gmt":"2026-01-25T21:18:49","slug":"genes-and-chromosomes","status":"publish","type":"post","link":"https:\/\/zogen.mx\/en\/genes-y-cromosomas\/","title":{"rendered":"Genes and chromosomes"},"content":{"rendered":"
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DNA, or deoxyribonucleic acid, is a complex molecule found in every cell of our body, containing the instructions necessary to create and maintain life. It is primarily composed of four chemical substances: adenine (A), thymine (T), guanine (G), and cytosine (C), which pair in a very specific way: A with T, C with G. Along these sequences of "letters," we can distinguish certain segments known as genes, which contain the information necessary to produce proteins that, as we will see below, are essential for the proper functioning of the organism.<\/p>\n\n\n\n

The complete set of DNA, that is, our genetic material, is called the genome. With few exceptions, every cell in the body contains a copy of our entire genome. If we think about it, we might imagine that all our DNA is a single, very long molecule. However, this is not the case, as it is divided into a series of unequal segments that, thanks to other molecules, are compacted and form what we know as chromatin. When cells divide, the chromatin reaches its highest degree of compaction, forming chromosomes.<\/p>\n\n\n\n

Chromosomes<\/strong><\/h2>\n\n\n\n

As you just saw, chromosomes are compacted packages of DNA. In humans and other organisms, they are not found free in the cell, but are contained within a structure called the cell nucleus.<\/p>\n\n\n\n

DNA contains the instructions necessary to create and maintain life, so, as you can imagine, each organism contains a different number of chromosomes. For example, a dog's cells contain 78 chromosomes, and an elephant's cells contain 56.<\/p>\n\n\n\n

A curious fact: one of the organisms with the most chromosomes that we know of are ferns, which have more than 100 chromosomes, and the one with the fewest is the ant Myrmecia pilosula, which only has one.<\/p>\n\n\n\n

How many chromosomes do humans have?<\/strong><\/h2>\n\n\n\n

Well, in our case, each human cell has 46 chromosomes, organized into 23 pairs. That is, we have two copies of each chromosome, one from our father and one from our mother. This occurs in all the cells of our body, except for sex cells, that is, eggs and sperm, which contain only 23 chromosomes.<\/p>\n\n\n\n

This makes it possible that, when both cells (egg and sperm) unite, a zygote is formed which will give rise to an embryo whose cells will have the 23 pairs of chromosomes, one copy of which is from each parent.<\/p>\n\n\n\n

Are chromosomes the same?<\/strong><\/h2>\n\n\n\n

Each chromosome contains information with different instructions for the maintenance and functioning of the organism and, therefore, they are different from each other.<\/p>\n\n\n\n

In the case of humans, as we have seen, we have 23 pairs: 22 of them are called autosomes, while the 23rd pair is called the sex chromosome. This differs between the sexes:<\/p>\n\n\n\n

\u2013 In the case of women, chromosome 23 is composed of two X copies (XX).<\/p>\n\n\n\n

\u2013 In the case of males, chromosome 23 consists of one X copy and one Y copy (XY).<\/p>\n\n\n\n

How are chromosomes formed?<\/strong><\/h2>\n\n\n\n

As we have seen, DNA molecules are very long, so the formation of chromosomes is essential for cell division. Logically, both resulting cells must have the same genetic information, so when cells divide, the genetic information is duplicated before forming two daughter cells.<\/p>\n\n\n\n

DNA is shaped like a double helix. Imagining a spiral staircase can help you visualize it. It is found in the cell nucleus, where the double helix folds around proteins called histones and forms a structure called a nucleosome.<\/p>\n\n\n\n

Nucleosomes and chromatin<\/strong><\/h2>\n\n\n\n

These nucleosomes (double helices folded around a set of proteins) gradually come together and form a structure resembling a string of beads, which continues to compact further until it generates another structure called chromatin, in which other molecules (proteins and RNA) participate. When chromatin reaches its maximum degree of compaction, it gives rise to chromosomes.<\/p>\n\n\n\n

When a cell divides, as mentioned earlier, the genetic information is duplicated and X-shaped chromosomes are formed, which are visible under a microscope. If we take a picture of the nucleus and then arrange the chromosomes in pairs, we can obtain what is called a karyotype, in which the chromosomes look like this:<\/p>\n\n\n\n

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\nhttps:\/\/www.genome.gov\/genetics-glossary\/Karyotype\n<\/div><\/figure>\n\n\n\n

But if we want to take a closer look at a chromosome, this is the structure we would find:<\/p>\n\n\n\n

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\nhttps:\/\/www.genome.gov\/genetics-glossary\/Centromere\n<\/div><\/figure>\n\n\n\n

Types of chromosomes based on the centromere<\/strong><\/h2>\n\n\n\n

As we can see in the image, when a cell is about to divide, the chromosomes are made up of two sister chromatids, which contain the same genetic information. These are joined by a constriction called the centromere, which, as we can see, divides the chromatids into arms. The length of the chromatid arms depends on the location of the centromere on the chromosome. Based on this, there are different types of chromosomes, which we explain below:<\/p>\n\n\n\n