Need Help With Some Sample Test Question

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Need Help With Some Sample Test Question

Post by asianmonk » Thu Mar 01, 2012 9:20 am

1. A person from another college is convinced that the recessive allele in Sickle Cell Disease is a bad condition because it causes the disease. He canʼt explain why it remains in the human population and natural selection hasnʼt got rid of it. Help him out. Explain the situation as you understand it.

2. Huntingtonʼs chorea is a dominantly inherited disease of the nervous system that usually starts to appear in affected individuals after the age of 35 and will eventually cause the death of these individuals. Other lethal, dominantly inherited diseases that appear in young individuals (before the age of 10) are much less common in the human population. Explain this difference in the frequency of these two types of dominantly inherited lethal diseases using concepts of natural selection.

3.Often, when describing the pattern of inheritance of diseases associated with recessive alleles, people talk about
the disease skipping a generation (e.g. observed in some individuals of the grand parents generation, skipped the
all individuals in parents generation, and observed in some of the children). Describe how that skipping pattern
might develop. Will these diseases always show a pattern of skipping a generation? Explain

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Post by Mike72 » Thu Mar 01, 2012 4:14 pm

1. If a disease remains in a population, it may be that it provides a survival advantage... or is just 'bad' e.g. genetic diseases with mutations that appear de novo, therefore are maintained in a population [The solution is on Wikipedia!]

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Re: Need Help With Some Sample Test Question

Post by HelpPleaseThankYou » Fri Mar 02, 2012 6:34 am

1. Because Natural Selection involves Fitness and that is determined by the proliferation of the species due to reproduction and is not based on disease or longevity. As for Sickle Cell, it's only considered "bad" in certain regions of the world where in others, it is beneficial, i.e. Malaria.

2. Just because the person becomes symptomatic at the age of 35 and subsequently succumbs to the disease does not mean the person has not reproduced, therefore, it has no bearing on Natural Selection or Fitness; said person could have reproduced many times and fit the criteria for "survival of the fittest." It also depends on the the parents and which genes they are carrying.

3. Read more about Autosomal dominant/recessive and X-linked dominant/recessive inheritance if you want to understand this further...

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Post by JackBean » Tue May 15, 2012 9:47 am

2. as HPTY said, person at 35 may have already children and moreover, Huntington's disease has slow progression so even after that age one can still have children, although is diagnosed. On the other hand, at the age of 10 one has hardly some kids.

Cis or trans? That's what matters.

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