What is alleles in biology

There are various versions of the shirt gene, those various versions or brands are the different alleles. I have the shoe gene. Right now I'm using the dress shoe allele. If I went out running I would put on the sneaker version or allele for that particular shoe. I don't talk about the shoe allele of the shirt gene. I don't wear those. Now, something else to understand is taht alleles can be dominant or they can be recessive. A dominant allele is one that will show itself in a cell or in a person's body.

So for example the detached earlobe, the free earlobe is the dominant allele for this particular gene. For the earlobe gene. Whereas the attached earlobe shape that allele is recessive which means you don't see its effects unless it's paired up with an identical attached earlobe allele. Now when you're naming alleles, what you do is you pick a letter that represents the gene. An incredible number of genes and gene forms underly human genetic diversity, and they are the reason why no two people are exactly alike.

In a simplified model, we will assume that there is only one gene that encodes for eye color although there are multiple genes involved in most physical traits. Blue, green, brown, and hazel eyes are each encoded by unique alleles of said gene. When humans procreate, the child receives 23 chromosomes long strands of DNA from each parent.

Each matching chromosome pair contains the same set of genes, with unique genes located at certain spots known as the gene locus. This inheritance means that individuals have two gene copies for a given trait, one inherited from their mother and the other from their father.

These are known as maternal alleles and paternal alleles. It is how these alleles interact that is responsible for unique characteristics. But not all gene variations will be expressed. For instance, you might have one allele for brown eyes and another for blue eyes, but you will not therefore have one blue and one brown eye. Individuals do not display the characteristics encoded on each matching pair of genes.

Instead, the genes that are expressed result in the phenotype , which is how genes are expressed in observable characteristics. Further Exploration Concept Links for further exploration gene recessive dominant test cross genotype phenotype haplotype DNA chromosome Hardy-Weinberg equilibrium evolution mutation speciation penetrance SNP allele frequency Hardy-Weinberg equation population bottleneck principle of segregation principle of independent assortment dihybrid cross genetic drift lethal allele principle of uniformity Principles of Inheritance.

Related Concepts You have authorized LearnCasting of your reading list in Scitable. Do you want to LearnCast this session? Some genes could have more than two alternative allelic forms. Many know human genes have multiple alleles.

Each individual can have only two alleles of each gene. However, some genes could have hundreds of alleles within a population. Therefore, multiple alleles of a given gene do not necessarily mean variation in the phenotype.

Multiple alleles are also used to describe all mutations found in a gene in a population. For example, multiple loss-of-function mutations can be reported in a population of patients suffering from a genetic disease. Although different mutations lead to the same result, loss of protein function, each mutation constitutes a different mutant allele as long as it is located in a different gene site. Beta-thalassemia is characterized by the reduction or absence of beta-globin chains of the hemoglobin.

They are non-coding DNA sequences but can be linked to specific genetic conditions. However, the primary and most successful application of STR markers is forensic analysis. The number of repeats in each STR locus is highly variable between individuals. Scientists used these variations within a population and developed a test for forensic identification using multiple STR markers.

Going back to the discussion of the ABO blood groups, genetic variation between alleles could lead to a protein variation. Even a small variation in protein level, four amino acids, in this case, can result in drastic effects on the phenotypes. Therefore, it can be said that one of the significant factors contributing to the genetic variation observed between individuals is the allelic variation between their genes. The blood group and flower color phenotypes are examples of discontinuous variation , where a trait is found in two or more distinct alternative forms.

In this type of variation, the different phenotypes can be easily distinguished. Geneticists use the term polymorphism to describe the traits with two or more common phenotypes in a population and morphs to describe the individual phenotypes. In some cases, rare, exceptional phenotypes occur; these are called mutants, and the more common normal phenotype is called wild-type. Although both polymorphisms and mutations originate from DNA sequence changes, somehow, polymorphism changes became more common.

The second type of genetic variation is called continuous variation. In this type of variation, a trait shows a continuous range of phenotypes that cannot be distinguished as distinct phenotypes, as is the case with the discontinuous variation.

Examples of characters that show continuous variation include weight, height, eye color, and similar measurable characteristics. Such traits are usually encoded by more than one gene; analyzing these phenotypes is more complicated than those showing discontinuous variation. Most genes code for proteins that directly express the trait.