One gen is a fragment of DNA that stores genetic information for protein synthesis or regulation. One allele each version is different from a gene for the same protein. For example, the ABO gene encodes the human blood group protein ABO, which has at least three alleles: A, B, and O.
Genes determine the physical and biochemical characteristics that an individual will have. They are manifested through visible physical features (phenotype), such as the color of the skin or eyes, as well as the functioning of the body.
One allele is a specific variation in the DNA sequence of a gene that determines how genetic traits will be expressed to the individual. For example, the androgen receptor gene has several alleles, one of which is associated with hair loss in men (baldness or androgenic alopecia).
|Definition||It is a fragment of DNA that contains genetic information for the synthesis of a protein.||It is a possible variation of a gene in a species.|
No coding: with information to synthesize proteins.
Nothing non-coding: act as regulators of protein synthesis.
Nothing constitutive: are expressed continuously.
No housework: maintain the basic functions of the cell.
Nothing optional: only expressed under certain conditions.
Nothing inducible: are expressed in response to certain stimuli.
Dominant alleles: is expressed whenever it is present.
Recessive alleles: is expressed only when presented in identical pairs.
Wild alleles: is the allele that is predominantly expressed in the majority of the population of a species
Mutant alleles: any allele other than the wild.
|Quantity||In diploid eukaryotic cells they occur in pairs, one from the father and one from the mother.||There can be multiple alleles for each gene.|
There is a gene for eye color, blood type, hair type and skin color.
Whether the eyes are blue or brown eyes; blood, type A or B; hair, curly or straight, and skin, light or dark.
What is a gene?
The gene is the functional unit of inheritance. It consists of a fragment of DNA (deoxyribonucleic acid) that contains the genetic information for the synthesis of a protein. Proteins are the macromolecules that perform the main functions of a cell.
The word “gene” comes from the Greek root people, which means ‘race’ or ‘origin’. Gregor Mendel (1822-1884) was the first to describe genes as “inheritance packages.”
The set of genes in an individual is known as the genome and determines the genotype or DNA sequence of the genome. He phenotype it is represented by the visible and measurable characteristics and features of the living being.
The position on the chromosome of a gene is called the locus. For example, the insulin gene (INS) is found on human chromosome 11 at the 11p15.5 locus, while the gene for melanocortin receptor 1 (MC1R), which is responsible for skin pigmentation, is located at the locus. 16q24.3.
Characteristics of genes
- It is made up of DNA.
- They are transmitted by inheritance from the parents.
- There are about 20,000 genes in humans.
- They are transcribed in the form of messenger RNA.
- They can undergo changes that produce a genetic mutation, giving rise to alleles.
- In eukaryotes, genes have coding sequences (exons) and non-coding sequences (introns).
Functioning of a gene
For gene information to be expressed in protein form, there are sequences in the DNA called promoters, which are the starting point for transcription. The enzyme responsible for “reading the gene” is RNA polymerase, which forms messenger RNA from the genetic sequence. Messenger RNA then translates into proteins in ribosomes.
Basically, genes store the code that transmits the specific biological characteristics of each living thing, from one generation to another.
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What is an allele?
An allele is any of the variations in DNA sequence that a gene can adopt. Each gene can have two or more alleles, the difference of which can range from a single nucleotide to the addition or removal of a piece of the sequence.
Each individual inherits an allele from the father and another from the mother, by the same gene, which may be the same or different. If the alleles are equal, it is a homozygous individual; when the alleles are different, the individual is heterozygous.
The word allele is an abbreviation of allelomorph, composed of the Greek word allelo-meaning ‘one to the other’, and –morphéwhich means ‘form’.
Characteristics of an allele
- It can be caused by a simple replacement of a nucleotide, by insertion of nucleotides or by removal of nucleotides.
- They occupy the same locus on the chromosomes.
- They can be “wild” when the allele is predominantly expressed in a species, or “mutant” when it differs from the wild.
- When is it dominant: Determines features visible to the next generation.
- When is it recessive: is present, but not manifested, in the set of visible dashes.
- If there are two recessive alleles inherited from the parents, the traits of these alleles are manifested.
Origin of alleles
Alleles originate from the substitution, insertion, or deletion of nucleotides in the DNA sequence of the gene. For example, protein Na 1.7 (which is a sodium channel) is encoded by the gene SCN9A which may have different alleles:
|Gen.||Gene sequence change||Allele|
|SCN9A||A cytosine C is replaced by a thymine T at position 829||829 C> T|
|SCN9A||A cytosine C is replaced by an adenine A at position 984||984 C> A|
|SCN9A||A guanine G is exchanged for an adenine A at position 5067||5067 G> A|
|SCN9A||A T thymine is inserted at position 2076||2076_2077insT|
|SCN9A||Nucleotides from 3703 to 3713 are removed||3703_3713del|
Functioning of an allele
Alleles contain information about specific traits that each gene possesses. These traits may manifest (it is possible to see them) or they may be hidden (even if they are present). For example, in rabbits, the color of the coat is determined by the C gene, which has four alleles:
- Brown c+: brown rabbits are considered wild, which is considered the “normal” phenotype.
- Albino color c: Rabbits homozygous for this allele do not produce pigment and have white fur and pink eyes.
- Chinchilla color cch: these rabbits are gray.
- Himalayan color ch: These rabbits are white but have dark fur on their legs, ears and nose.
When one of the alleles is expressed in the phenotype (manifests), it is called dominantwhile the allele that is not expressed in an individual is called recessive. For example, any rabbit with the dominant allele c+ will be brown (c+c, c+cch o c+ch). The recessive allele c it will only be evident in homozygous rabbits CC.
Homozygous and heterozygous
Most diploid organisms have chromosome pairs inherited from both parents. Each of these chromosomes has an allele of one gene. If the two alleles are in the same place (locus) of their respective chromosome are equalthe cell or individual is homozygous. When alleles are located in it locus of the chromosome are differentthey are called heterozygotes.
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