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Recessive gene and dominant gene

  1. Jun 17, 2012 #1
    Like the title,
    1)Are recessive gene genetic variations of a dominant gene(or normal gene).
    2)What is the origin of a recessive gene?
    3)Are recessive genes bought on by genetic mutations ?

    I know the questions are trivial, but I am not able to clear these concepts.
  2. jcsd
  3. Jun 17, 2012 #2


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  4. Jun 17, 2012 #3


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  5. Jun 17, 2012 #4
    These questions are far from trivial.

    The molecular basis of gene dominance has a lot to do with the chemical pathways that lead to a particular phenotype being expressed. Here are links to review article on the mechanisms of gene dominance.

    “Dominance typically occurs when one of the two alleles is non-functional at the molecular level, that is, it is not transcribed or else does not produce a protein product. This can be the result of a mutation that alters the DNA sequence of the allele. An organism homozygous for the non-functional allele will generally show a distinctive phenotype, due to the absence of the protein product. For example, in humans and other organisms, the unpigmented skin of the albino phenotype[8] results when an individual is homozygous for an allele that prevents synthesis of the skin pigment protein melanin. It is important to understand that it is not the lack of function that allows the allele to be described as recessive: this is the interaction with the alternative allele in the heterozygote.”

    “The molecular basis of genetic dominance

    "This review draws on the rapid expansion in knowledge of molecular and cellular biology to classify the molecular mechanisms of dominant mutation. The categories discussed include (1) reduced gene dosage, expression, or protein activity (haploinsufficiency); (2) increased gene dosage; (3) ectopic or temporally altered mRNA expression; (4) increased or constitutive protein activity; (5) dominant negative effects; (6) altered structural proteins; (7) toxic protein alterations; and (8) new protein functions.”

    “Gene Interaction
    Interactions between Alleles Produce Dominance Relationships”
    Last edited: Jun 17, 2012
  6. Jun 17, 2012 #5
    You are right. This is an important distinction when one allele controls two phenotypic features.
    The expression of a particular phenotypic feature is dominant or recessive. However, one allele can control several different phenotypic features, each of which has a different ranking.
    For example, consider the allele that usually determines sickle cell anemia.
    The allele (i.e., chromosome locus) that controls sickle cell anemia has two genes. Gene A is associated with both sick cell anemia and malaria resistance. Gene B is associated with being free of sickle cell anemia and malaria predisposition.
    Gene A is dominant with respect to malaria resistance but recessive with respect to sickle cell anemia. Gene B is recessive with respect to malaria predisposition but dominant with respect to freedom from sickle cell anemia.
    If you do the arithmetic (Punnet squares), you find that this means the following. The heterozygous AB person with both genes A and B has no sickle cell anemia and is resistant to malaria. However, a homozygous AA is resistant to malaria but has sickle cell anemia. A homozygous BB person is not resistant to malaria but doesn't have sickle cell anemia.
    In an area with lots of mosquitoes and the malaria parasite, natural selection favors a mixed population with both A and B genes.
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