What makes a mutation recessive

Prev Next. View All Replies 2. Latest Reply:. Hello Mithun, Why are more mutations recessive instead of dominant? The definitions of dominant and recessive are fairly straightforward when we talk about them in terms of the appearance of traits.

But the molecular basis for dominance and recessiveness can be highly variable. Every gene and allele has its own story. What do we mean when we talk about dominant or recessive alleles? An allele is a form of a gene. A specific allele is dominant with respect to a phenotype if the phenotype is the same, whether the allele is homozygous or heterozygous.

A recessive allele only shows its phenotype when it is homozygous. Oftentimes, when a mutant allele produces a nonfunctional protein or a protein with decreased function, that allele is recessive. In such cases, a heterozygote would show the phenotype associated with the functional allele. One example of this type of pattern can be seen in cystic fibrosis, which is associated with the CFTR gene. The mutant alleles of the CFTR gene are recessive, so individuals must have two copies of the mutant alleles to develop the symptoms of cystic fibrosis.

Rent this article via DeepDyve. Allendorf W. Nature 76— Campos-Ortega J. Chandra H. In Genomic imprinting. Development suppl. In Sex chromosome and sex-determining genes ed. Reed and J. Graves Switzerland: Harwood Academic Publishers. Google Scholar. Charlesworth B.

Nature — Article Google Scholar. Fisher R. Forsdyke A. Gautan N. Haldane J. London B — Hall B. Often though, morphological mutants are the direct result of a mutation in a biochemical pathway. In humans, albinism is the result of a mutation in the pathway from converts the amino acid tyrosine to the skin pigment melanin. Similarly, cretinism results when the tyrosine to thyroxine pathway is mutated. Therefore, in a strict genetic sense, if appropriate experiments are performed, a morphological mutation can be explained at the biochemical level.

For some mutations to be expressed, the individual needs to be placed in a specific environment. This is called the restrictive condition. But if the individual grow in any other environment permissive condition , the wild type phenotype is expressed. These are called conditional mutations. Mutations that only expressed at a specific temperature temperature sensitive mutants , usually elevated, can be considered to be conditional mutations. Single gene disorders are caused by DNA changes in one particular gene, and often have predictable inheritance patterns.

If you have any other comments or suggestions, please let us know at comment yourgenome. Can you spare minutes to tell us what you think of this website? 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.