Why are diseases caused by a dominant allele expected to disappear?

Answer 1

I'm not sure that they are. I'd've thought, if anything, the ongoing efforts of modern medicine to combat genetic disorders remove the evolutionary pressure that would originally have caused those with unfavourable genetic abnormalities to be out-competed and thus rendered extinct. Thus one would expect to see an increasing incidence of genetic abnormalities in the coming years.

Answer 2

If a disease is caused by a dominant allele, there are only two phenotypes, affected and unaffected - there are no carriers and so no way for an allele to 'hide' from selection.

Assuming the allele causes a disorder that is genuinely deleterious (i.e. it is not so mild that it is barely noticeable), in most cases the impact of that allele will be felt some time between birth and first reproduction. In this case the chances are that it will either kill you or reduce your fitness (in the genetic sense) to such a degree that affected individuals will not reproduce (or in the case of humans only, perhaps choose not to), so the allele will never be passed on and that disease will completely disappear until it arises again by new mutation.

The most well-known example of a dominant allele is that causing Huntingdon's disease. It continues to persist because the disease is late onset and by the time someone is diagnosed, they have frequently had families and there is a 50% chance for each child that they have inherited it.

So, it is the reduced chance of surviving to reproduction that causes these alleles to generally disappear more quickly than recessive ones, which are more common in carriers than in affected individuals.

Answer 3

A dominant allele will always show itself, so if it is passed on, the result will be a diseased individual. This should make it less likely that the allele will be passed on, since the patient is more likely to die before having offspring. A recessive allele is able to slip through generations, being passed on for many years, and only being shown when 2 defective copies come together. as mentioned above, modern medicine does all it can to prolong life, allowing disease causing alleles to be passed on more readily. This is only really the case in humans though, where morals play an important part. In the rest of nature, its still about survival of the fittest.

Answer 4

The dominant allele means the bit of DNA (gene) which shows itself even if there is another one present.

If you have an hereditary disease caused by a dominant allele, you probably will have a shorter life; not have many children if any and therefore this gene will eventually not be passed on.

If you have a disease that is a recessive allele then it can be passed on because people can be carriers of it and not realise; and if they just happen to have a child with someone who also is a carrier, the child will have this disease (but not always).

Answer 5

Ordinarily, a dominant allele that kills half the offspring of an individual would be selected against in a population and disappear over time.

Answer 6

You clean up those by using using genetic diagrams. Like multiplication squares. Say the ailment became into Huntingdons that's brought about by using a dominant allele and the mother had the ailment and the father did not h h H Hh Hh h hh hh So there's achieveable of fifty% that they'll bypass it on. ought to be the two homozygous or heterozygous for the allele. wish this permits!