They are the functional units of heredity, also known as a segment of the appropriate DNA sequence to a protein, a group of protein variants, or structural RNA molecules that do not originate proteins.
The Human Genome Project established that the human being has in his genome 20,000-25,000 genes in the 3 billion base pairs of DNA. The fruit fly Drosophila melanogaster contains approximately 14,000 genes in 137 million base pairs, and the plant Arabidopsis thaliana has 26,000 genes in 142 million base pairs of DNA.
Genes in eukaryotic cells exhibit:
- Promoter region: DNA sequence that precedes the series that codes for a protein. It is the region that inspects the transcription of the gene.
- Coding region: DNA sequence transcribed into mRNA and then translated into an amino acid sequence.
- Exons: DNA sequences that occur in the definitive messenger RNA.
- Introns: Intermediate sequences that are annulled in messenger RNA.
types of genes
There are different types of genes and they are the following:
- Structural genes: like the ACTB gene that codes for the protein actin, it is essential in the cytoskeleton of the cell.
- Regulatory genes: encode for proteins that encode the transcription of other genes.
- Specialized genes: only enunciated in certain cells; for example the globin gene in the precursors of red blood cells.
- Maintenance or constitutive genes are genes whose transcription is invariable in the cell and which carry out its basic functions.
- Pseudogenes: they are non-functional genes, the result of the accumulation of mutations.
These have information that establishes the characteristics of the species, they also inspect the development and functions of cells. The BRCA1 gene on chromosome 17 in humans encodes a protein that maintains genome stability and acts as a tumor suppressor.
They are threadlike organizations that are located inside the nucleus that is composed of DNA and proteins. Eukaryotic cells of each species of living being contain a characteristic fixed and constant number of chromosomes.
Chromosomes can be seen under a microscope when cells begin to separate. In a given species, the chromosomes can be known by their number, size, centromere position, and banding pattern. The karyotype is the number and appearance of human chromosomes.
In bodies where there is sexual reproduction, the sexual cells or gametes have only one set of the chromosomes of the species, that is, they are haploid.
The number of chromosomes is not related to the complication of the organism, for example, in the somatic cells of people there are 46 chromosomes, in mice 42, in cattle 60.
Each chromosome has the following:
- A narrowing called the centromere.
- End ends that are called as telomeres.
- Two arms, one small or p-arm (for the French petit) and one long or q-arm.
Chromosomes are classified into:
- Somatic chromosomes: they are similar chromosomes between individuals of a species, regardless of their sex. In humans there are 22 pairs of somatic chromosomes known as homologous chromosomes.
- Sex chromosomes: are two chromosomes that determine the sex of the subject. In humans, one pair of X chromosomes (XX) determines that the individual is female, while one X chromosome and one Y chromosome (XY) establishes that the individual is male.
Chromosomes are classified according to the position of the centromere in:
- Metacentric chromosomes: the centromere is in the middle of the chromosome.
- Submetacentric chromosomes: the centromere is at one end.
- Acrocentric chromosomes: the centromere is close to the end, which generates a very small p arm.
- Telocentric chromosomes: the centromere is located exactly at the end.
function of chromosomes
Its main function of chromosomes is the packaging of DNA within the nucleus. The DNA of the person reaches more than 3 billion base pairs that if it could be extended would measure 2 meters, however, the nucleus barely measures 0.000006 meters.
Chromosomal disorders where there is a change in the number of chromosomes of the species are identified as aneuploidy and within them we find:
- Trisomy: due to the presence of an extra chromosome in the cell. For example, Down syndrome or trisomy 21 is known to have three copies of chromosome 21, instead of the normal two copies.
- Monosomy: due to the absence of a chromosome in the cell. For example, Turner syndrome, where there are only 45 chromosomes with only one X chromosome.
Genes and Chromosomes
|Definition||functional unit of heredity.||Linear packaging structure of DNA.|
|Location||in the chromosomes.||in the cell nucleus.|
|Composition||DNA.||Chromatin: DNA and proteins.|
|According to function in the cell:
somatic chromosomes or autosomes
X and Y sex chromosomes.
According to location of the centromere:
|examples||ACTB gene: actin gene.
BRCA1 gene: tumor suppressor gene.
INS gene: insulin gene.
|Homo sapiens: 46 chromosomes.
Mus musculus: 40 chromosomes.
Gorilla gorilla: 48 chromosomes.