A gene It is a fragment of DNA that stores the genetic information for the synthesis of a protein or its regulation. A allele it is each different version of a gene for the same protein. For example, the ABO gene codes for the ABO human blood group protein that 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 traits (phenotype), such as skin or eye color, as well as the functioning of the organism.
A allele It is a specific variation in the DNA sequence of a gene that determines how genetic characteristics will be expressed in 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).
Gene Allele Definition It is a fragment of DNA that contains the genetic information for the synthesis of a protein. It is a possible variation of a gene in a species. Guys
Coding genes: with information to synthesize proteins.
non-coding genesThey act as regulators of protein synthesis.
housekeeping genes: are expressed continuously.
housekeeping genesThey maintain the basic functions of the cell.
facultative genes: are only expressed under certain conditions.
inducible genesThey are expressed in response to certain stimuli.
dominant alleles: is expressed whenever it is present.
recessive alleles: is expressed only when it occurs in identical pairs.
wild type allelesis the allele that is predominantly expressed in the majority of the population of a species
mutant alleles: any allele other than wild type.
Quantity In diploid eukaryotic cells they occur in pairs, one from the father and one from the mother. For each gene there can be multiple alleles. examples
There is a gene for eye color, blood type, hair type, and skin color.
The one that 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 heredity. 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 carry out the main functions of a cell.
The word “gene” comes from the Greek root genos, meaning ‘race’ or ‘origin’. Gregor Mendel (1822-1884) was the first to describe genes as “packages of heredity”.
The set of genes of 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 a locus. For example, the gene for insulin (INS) is located on chromosome 11 in humans at locus 11p15.5, while the gene for melanocortin receptor 1 (MC1R), responsible for skin pigmentation, is located at the 16q24.3 locus.
Gene characteristics
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
In order for the gene information to be expressed in the form of a protein, there are sequences in the DNA called promoters, which are the start site of transcription. The enzyme in charge of “reading the gene” is RNA polymerase, which forms messenger RNA from the genetic sequence. Messenger RNA is then translated into proteins on ribosomes.
Basically, the genes are stored in the code that transmits the specific biological characteristics of each living being, from one generation to another.
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What is an allele?
An allele is any of the DNA sequence variations 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 deletion of a piece of its sequence.
Each individual inherits one allele from the father and one from the mother, for the same gene, which may be the same or different. If the alleles are the same, it is a homozygous individual; when the alleles are different, the individual is heterozygous.
The word allele is an abbreviation of allelomorph, it is composed of the Greek word allele-which means ‘from one to another’, and –morphewhich means ‘shape’.
Characteristics of an allele
It can be caused by a simple substitution of a nucleotide, by insertion of nucleotides or by deletion of nucleotides. They occupy the same locus on the chromosomes. They can be “wild” when it is the predominantly expressed allele in a species, or “mutant” when it differs from wild. When is dominant: determines visible characteristics in the next generation. When is recessive: It is present, but without manifesting itself, in the set of visible features. If there are two recessive alleles inherited from the parents, the traits of these alleles are manifested.
Origin of alleles
Alleles arise from the substitution, insertion, or deletion of nucleotides in the DNA sequence of the gene. For example, the protein Na 1.7 (which is a sodium channel) is encoded by the gene SCN9A that can present different alleles:
Gene Change in gene sequence Allele SCN9A A cytosine C is changed to a thymine T at position 829 829 C>T SCN9A A cytosine C is changed to an adenine A at position 984 984 C>A SCN9A A guanine G is changed by an adenine A at position 5067 5067 G>A SCN9A A thymine T is inserted at position 2076 2076_2077insT SCN9A Nucleotides from 3703 to 3713 are deleted 3703_3713del
functioning of an allele
Rabbit fur color is determined by different alleles.
Alleles contain information about specific traits that each gene possesses. These traits can be manifest (it is possible to see them) or they can be hidden (even if they are present). For example, in rabbits coat color is determined by the C gene which has four alleles:
Brown color c+: Brown rabbits are considered the wild type, 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 have gray color. Himalayan color ch: These rabbits are white but have dark fur on their feet, 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 or c+ch). the recessive allele c will only be evident in homozygous rabbits DC.
Homozygous and heterozygous
Most diploid organisms have pairs of chromosomes inherited from both parents. Each of these chromosomes has an allele of a gene. If the two alleles located at the same locus (loci) of their respective chromosome are equalthe cell or individual is homozygous. When alleles located on the same loci of the chromosome are differentthey are called heterozygous.
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