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. Or it can refer to a disease. Huntington's disease, for instance, is a dominant mutation where, if one is carrying that version of the Huntington gene, that mutation, that dominant mutation, will give the individual the disease regardless of what that person's other Huntington's disease gene allele is.
That other Huntington's disease gene allele can be perfectly normal, but the person still has the disease because of that one copy of the Huntington's disease gene that is mutated. A dominant allele produces a dominant phenotype in individuals who have one copy of the allele, which can come from just one parent. For a recessive allele to produce a recessive phenotype, the individual must have two copies, one from each parent.
An individual with one dominant and one recessive allele for a gene will have the dominant phenotype. Dominant and recessive inheritance are useful concepts when it comes to predicting the probability of an individual inheriting certain phenotypes, especially genetic disorders. But the terms can be confusing when it comes to understanding how a gene specifies a trait.
This confusion comes about in part because people observed dominant and recessive inheritance patterns before anyone knew anything about DNA and genes, or how genes code for proteins that specify traits. The critical point to understand is that there is no universal mechanism by which dominant and recessive alleles act. Whether an allele is dominant or recessive depends on the particulars of the proteins they code for. The terms can also be subjective, which adds to the confusion.
The same allele can be considered dominant or recessive, depending on how you look at it. The sickle-cell allele, described below, is a great example. However, these patterns apply to few traits. Sickle-cell disease is an inherited condition that causes pain and damage to organs and muscles.
Instead of having flattened, round red blood cells, people with the disease have stiff, sickle-shaped cells. The long, pointy blood cells get caught in capillaries, where they block blood flow. The disease has a recessive pattern of inheritance: only individuals with two copies of the sickle-cell allele have the disease.
People with just one copy are healthy. In addition to causing disease, the sickle-cell allele makes people who carry it resistant to malaria, a serious illness carried by mosquitos.
Malaria resistance has a dominant inheritance pattern: just one copy of the sickle cell allele is enough to protect against infection. This is the very same allele that, in a recessive inheritance pattern, causes sickle-cell disease!
People with two copies of the sickle-cell allele have many sickled red blood cells. People with one sickle-cell allele and one normal allele have a small number of sickled cells, and their cells sickle more easily under certain conditions. So we could say that red blood cell shape has a co-dominant inheritance pattern. That is, individuals with one copy of each allele have an in-between phenotype. Open survey. In: Facts In the Cell. Since human cells carry two copies of each chromosome they have two versions of each gene.
These different versions of a gene are called alleles. 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.
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