What happens if both alleles are dominant

Alleles can be either dominant or recessive. Dominant alleles show their effect even if the individual only has one copy of the allele also known as being heterozygous. For example, the allele for brown eyes is dominant, therefore you only need one copy of the 'brown eye' allele to have brown eyes although, with two copies you will still have brown eyes. If both alleles are dominant, it is called codominance.

The resulting characteristic is due to both alleles being expressed equally. An example of this is the blood group AB which is the result of codominance of the A and B dominant alleles. Recessive alleles only show their effect if the individual has two copies of the allele also known as being homozygous. For example, the allele for blue eyes is recessive, therefore to have blue eyes you need to have two copies of the 'blue eye' allele.

Related Content:. What is a gene? A dominant gene, or a dominant version of a gene, is a particular variant of a gene, which for a variety of reasons, expresses itself more strongly all by itself than any other version of the gene which the person is carrying, and, in this case, the recessive.

Now, it usually refers to inheritance patterns frequently used in conjunction with a Punnett square where, if an individual has two versions of a gene, and one is observed to frequently be transferred from one generation to another, then it is called dominant.

Biochemically, what is going on in this case is that the genetic variation, for a variety of reasons, can either induce a function in a cell, which is either very advantageous or very detrimental, which the other version of the gene can't cover up or compensate for. In that case, you're going to have a dominant mutation, and that dominant mutation can be benign.

It can refer to eye color of one sort or another; that can be can a dominant mutation. However, it appears that the parasite reproduces more slowly in blood cells that have some modified hemoglobin. And infected cells, because they easily become misshapen, are more quickly removed from circulation and destroyed. To see more examples of how variations in genes influence traits, visit The Outcome of Mutation.

Dominant and recessive are important concepts, but they are so often over-emphasized. After all, most traits have complex, unpredictable inheritance patterns. However, at the risk of adding even more over-emphasis, here are some more things you may want to know:.

Looking at this, you might conclude that the dominant phenotype is twice as common as the recessive one. But you would probably be wrong. Recessive alleles can be present in a population at very high frequency. Consider eye color. Eye color is influenced mainly by two genes, with smaller contributions from several others. People with light eyes tend to carry recessive alleles of the major genes; people with dark eyes tend to carry dominant alleles.

In Scandinavia, most people have light eyes—the recessive alleles of these genes are much more common here than the dominant ones. Mode of inheritance has nothing to do with whether an allele benefits an individual or not. Take rock pocket mice, where fur color is controlled mainly by a single gene. The gene codes for a protein that makes dark pigment.

Some rock pocket mice have dark fur, and some have light fur. The dark-fur allele is dominant, and the light-fur allele is recessive. This page has been produced in consultation with and approved by:. The characteristic features of Angelman syndrome are not always obvious at birth, but develop during childhood. Latest research suggests that most cancers are caused by environmental rather than genetic factors.

Folic acid taken before conception, and during at least the first four weeks of pregnancy, can prevent around seven out of 10 cases of neural tube defects. Charcot-Marie-Tooth disease is the most common inherited disorder affecting the peripheral nervous system. Most cleft palates and cleft lips can be repaired so that appearance and speech develop normally.

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Skip to main content. Genetic conditions. Home Genetic conditions. Genes and genetics explained. Actions for this page Listen Print. Summary Read the full fact sheet. On this page. Chromosomes How we inherit characteristics Dominant and recessive genes Co-dominant genes Gene changes in cells Genetic conditions Genes and genetics — related parents Genetic counselling and testing Where to get help.

Chromosomes Humans typically have 46 chromosomes in each cell of their body, made up of 22 paired chromosomes and two sex chromosomes. How we inherit characteristics Parents pass on traits or characteristics, such as eye colour and blood type, to their children through their genes.

Examples of inheritance patterns include: autosomal dominant — where the gene for a trait or condition is dominant, and is on a non-sex chromosome autosomal recessive — where the gene for a trait or condition is recessive, and is on a non-sex chromosome X-linked dominant — where the gene for a trait or condition is dominant, and is on the X-chromosome X-linked recessive — where the gene for a trait or condition is recessive, and is on the X-chromosome Y-linked — where the gene for a trait or condition is on the Y-chromosome co-dominant — where each allele in a gene pair carries equal weight and produces a combined physical characteristic mitochondrial — where the gene for a trait or condition is in your mitochondrial DNA, which sits in the mitochondria powerhouse of your cells.

Eye colour The allele for brown eyes B is dominant over the allele for blue eyes b. Blood groups For blood groups, the alleles are A, B and O. Basic genetics , Learn. Give feedback about this page. Was this page helpful? Yes No. View all genetic conditions.