Do recessive deleterious alleles over time reach fixation or not? ?

4 Answers

  • CRR
    Lv 7
    2 months ago

    Probably not. As the proportion rises an increasingly larger proportion of the population get the double whammy (proportional to q^2) and will be weeded out.

    Take the sickle cell trait. In it's heterozygous form it provides some protection from malaria, but in the homozygous form it causes sickle cell anemia. As a result even in areas with lots of malaria the proportion never gets above 20%.

  • ?
    Lv 7
    2 months ago


    Take "long hair" for example.  That's prevalent in a lot of Out-Of-Africa populations.

    Or "blonde hair."  Very deleterious in Asia, fixed in some Europe and Scandinavia populations.

    Or "big-headed baby."  Deleterious because it caused about 2% death-in-childbirth.  Having a big brain outweighed that negative effect, apparently.  We're still around.  The smaller-brained hominins are gone.

  • 2 months ago

    IF you assume that there is no mutation that continues to produce the recessive allele, a lethal recessive allele will eventually be eliminated from the population. 

    If the allele is just deleterious but not lethal in the homozygous state, (and again, if there is no mutation producing that allele), then it will be eliminated, but will take a much longer time.

    However, all genes mutate, and so there is a mutation rate that will form that deleterious allele. When this is the case, the allele will reach a fixed level in the population that is related to its mutation rate and to the degree of selection against the homozygous recessive individuals.

    There is a free app for Mac and Windows machines called Allele A1. It allows you to model all types of situations related to H-W. The link to download it is here:

  • Anonymous
    2 months ago

    not sure what you mean by "reach fixation".

    The thing with recessive alleles is that you won't notice them unless you have them twice. So unless you have two patients making babies together, you mostly won't see them in the offspring

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