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Dominance (genetics)

TLDR: Dominance in genetics refers to one gene variant masking the effect of another variant of the same gene. The dominant variant overrides the recessive variant. This concept is important in understanding how traits are inherited.

In genetics, dominance is the phenomenon where one variant of a gene on a chromosome masks or overrides the effect of a different variant of the same gene on the other copy of the chromosome. The dominant variant is called dominant, while the second variant is called recessive. This occurs when an individual has two different variants of the same gene on each chromosome, which is caused by a mutation in one of the genes. The terms autosomal dominant or autosomal recessive are used to describe gene variants on non-sex chromosomes, while those on sex chromosomes have different inheritance patterns. There are also other forms of dominance, such as incomplete dominance and co-dominance.

Dominance is a key concept in Mendelian inheritance and classical genetics. It is often demonstrated using Punnett squares, which show the probability of different genotypes and phenotypes in offspring. A classic example of dominance is the inheritance of seed shape in peas, where round peas (associated with the dominant allele) mask the presence of wrinkled peas (associated with the recessive allele).

It's important to note that dominance is not inherent to an allele or its traits. It is a relative effect between two alleles of a given gene. One allele can be dominant over a second allele of the same gene, recessive to a third allele, and co-dominant with a fourth allele. Additionally, one allele may be dominant for one trait but not others.

The concept of dominance was first observed by Gregor Mendel, the "Father of Genetics," in the 1860s. However, it was not widely known until the early twentieth century. Mendel's experiments with garden peas showed that certain traits were always expressed in offspring, while others seemed to disappear. He hypothesized that each parent contributed one allele to the offspring, and that one allele dominated the expression of the other.

The dominance relationship between alleles is determined by their behavior at the molecular level. Genes are made up of DNA, which is transcribed into RNA and translated into proteins. Different alleles at a gene locus may or may not be transcribed, and if transcribed, they may produce slightly different versions of the same protein. The interaction between these proteins determines the phenotype.

There are different types of dominance, including complete dominance, incomplete dominance, and co-dominance. In complete dominance, one allele completely masks the effect of the other allele. In incomplete dominance, the phenotype of the heterozygous genotype is intermediate between the phenotypes of the homozygous genotypes. In co-dominance, both alleles contribute to the phenotype, resulting in a combined expression of traits.

It's important to note that dominance does not determine whether an allele is advantageous or deleterious. Dominant alleles can be beneficial, neutral, or harmful, depending on the specific trait and the environment. Additionally, dominance is not the same as epistasis, which is the phenomenon of an allele of one gene masking the effect of alleles of a different gene.

The understanding of dominance has evolved over time, and genetic nomenclature has been developed to describe the dominance relationships between alleles. The Hardy-Weinberg principle is a mathematical formula that can be used to estimate the frequency of carrier genotypes in a population.

In summary, dominance in genetics refers to the relationship between different variants of a gene, where one variant masks or overrides the effect of another variant. This concept is important in understanding how traits are inherited and expressed in offspring.

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