Dominant

Dominant refers to the relationship between two versions of a gene. Individuals receive two versions of each gene, known as alleles, from their parents. If the two alleles of a gene are different, one allele will be expressed; it is the dominant gene. The effect of the other allele, called recessive, is masked.

Dominant Allele

The Dominant allele is the variant of a gene that will always express itself if present. It can mask the presence of a recessive allele. In other words, if an individual has two different versions of a gene, the dominant allele is the one that will be expressed.

Recessive Allele

The Recessive allele is the variant of a gene that will only express itself if the dominant allele is not present. This means that the recessive trait will only be visible in individuals who have two copies of the recessive allele.

Dominant Disorders

Dominant disorders are diseases that are caused by a dominant allele. This means that an individual only needs one copy of the faulty gene to develop the disorder. Examples of dominant disorders include Huntington's disease and Marfan syndrome.

Recessive Disorders

Recessive disorders are diseases that are caused by a recessive allele. This means that an individual needs two copies of the faulty gene to develop the disorder. Examples of recessive disorders include cystic fibrosis and sickle cell anemia.

Co-Dominance

In some cases, neither allele is dominant or recessive. Instead, both alleles are expressed equally. This is known as co-dominance. An example of co-dominance is the AB blood type in humans.

Incomplete Dominance

Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele. This results in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles.

See Also

• Genetics
• Genome
• Chromosome
• DNA

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