A gene is a portion of deoxyribonucleic acid (DNA) that codes for a protein or RNA. A chromosome It is a nuclear structure that corresponds to the DNA packaging where a number of genes are found. That is, the chromosome is a large portion of DNA, the molecule responsible for the genetic information of living beings, which is expressed through genes.
Gene Chromosome Definition Functional unit of heredity Linear DNA packaging structure Location In chromosomes In cell nucleus Composition of DNA Chromatin: DNA and proteins Types
structural genes
regulatory genes
specialized genes
housekeeping genes
pseudogenes
According to function in the cell:
Somatic Chromosomes or Autosomes Sex Chromosomes X and Y
According to the location of the centromere:
Metacentric Chromosomes Submetacentric Chromosomes Acrocentric Chromosomes Telocentric Chromosomes Examples
ACTB gene: actin gene.
BRCA1 gene: tumor suppressor gene.
INS gene: insulin gene.
Human being (Homo sapiens): 46 chromosomes
Mouse(musculus): 40 chromosomes
Gorilla (gorilla gorilla): 48 chromosomes
What are genes?
Diagram of the location of the gene in the DNA and of the chromosome in the cell nucleus.
Genes are the functional units of heredity. A gene is defined as a segment of the DNA sequence corresponding to a protein, to a set of protein variants or to structural RNA molecules that do not produce proteins.
The Human Genome Project determined that the Human beings have 20,000 to 25,000 genes in their genome. in the 3 billion base pairs of DNA. The fruit fly Drosophila melanogaster has approximately 14 thousand genes in 137 million base pairs and the plant Arabidopsis thaliana owns approx. 26 thousand genes in 142 million base pairs of DNA.
Genes in eukaryotic cells have:
promoter region: DNA sequence that precedes the sequence that codes for a protein. It is the region that controls the transcription of the gene.
coding region: DNA sequence transcribed into mRNA to later be translated into an amino acid sequence.
Exons: DNA sequences that occur in the final messenger RNA.
introns: Intermediate sequences that are deleted in the messenger RNA.
gene types
Genes can be of the following types:
structural genes: as the ACTB gene that encodes the actin protein, important in the cytoskeleton of the cell.
regulatory genesThey code for proteins that regulate the transcription of other genes.
specialized genes: genes that are only expressed in certain cells; for example, the globin gene in red blood cell precursor cells.
maintenance genes or constitutive (of English housekeeping genes): are genes whose transcription is constant in the cell and which fulfill its basic functions.
pseudogenes: they are non-functional genes, the result of the accumulation of mutations.
gene function
Genes are the elements that contain the information that determines the characteristics of the species. They also control the development and functions of cells. For example, the BRCA1 gene on chromosome 17 in humans codes for a protein that maintains genome stability and acts as a tumor suppressor.
What are chromosomes?
Normal human chromosomes.
Chromosomes are thread-like structures found inside the nucleus, made up of DNA and proteins. The eukaryotic cells of each species of a living being have a fixed and constant number of characteristic chromosomes. For example, the human Homo sapiens It has 23 pairs of chromosomes or 46 chromosomes.
Chromosomes are visible under a microscope when cells begin to divide. In a given species, chromosomes can be identified by their number, size, centromere position, and banding pattern. He karyotype is the number and appearance of human chromosomes.
In organisms where there is sexual reproduction, the sex cells or gametes have half of the chromosomes of the species, that is, they are haploid. For example, in humans, eggs have 23 chromosomes and sperm also have 23 chromosomes.
The number of chromosomes is not related to the complexity of the organism. Such is the case of human somatic cells, where there are 46 chromosomes, while there are 42 in mice, and 60 in bovines.
chromosome structure
Each chromosome has:
a narrowing called centromere;
end points that are known as telomeres;
two arms, one small or p-arm (for the French little) and one long or arm q.
types of chromosomes
Scheme of human somatic chromosomes and sex chromosomes.
In living beings where two sexes differ, the chromosomes are classified into:
somatic chromosomes: are those identical chromosomes between individuals of a species, regardless of their sex. In humans there are 22 pairs of somatic chromosomes, also called homologous chromosomes.
sex chromosomesThey are a pair of chromosomes that determine the sex of the individual. In humans, a pair of X chromosomes (XX) determines that the individual is female, while an X chromosome and a Y chromosome (XY) determines that the individual is male.
Additionally, chromosomes can be 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 located at one end;
acrocentric chromosomes: the centromere is very close to the tail end, producing a very small p-arm;
telocentric chromosomes: the centromere is exactly at the end.
Chromosome function
The main function of chromosomes is the packaging of DNA within the nucleus. Human DNA comprises more than 3 billion base pairs, which if stretched out would be 2 meters, but the nucleus is barely 0.000006 meters!
Chromosomal abnormalities
Chromosomal disorders where there is a change in the number of chromosomes of the species is known as aneuploidy, within which we have:
trisomy: given by the presence of an extra chromosome in the cell. For example, Down syndrome or trisomy 21 is characterized by having three copies of chromosome 21, instead of the normal two copies.
monosomy: given by the absence of a chromosome in the cell. For example, Turner syndrome, where there are only 45 chromosomes with a single X chromosome.
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