Question R12 Q25 - NSB Round Robin 2013

Many diseases, including cystic fibrosis, are caused by recessive homozygosity [hoh-muh-zy-GOS-i-tee] of a particular gene. Since these diseases are caused by recessive genes, one might think that they should have been eliminated long ago. What is the leading theory on why diseases like cystic fibrosis still exist?

W) Individuals with the disease are able to have children before the effects of the disease emerge

X) A single recessive allele of the gene causing the disease may confer a selective advantage

Y) Two copies of the recessive allele of the gene causing the disease may confer a selective advantage

Z) Individuals that are heterozygous [het-er-uh-ZY-guhs] for the gene causing the disease are as healthy as normal individuals

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