Explain how a mutant CC-CKR5 allele offers protection from HIV infection
What will be an ideal response?
Normal alleles of the CC-CKR5 gene encode a cell-surface protein that signals the immune system when an infection is present. HIV binds to this protein and uses it to infect T4 helper cells. The mutant allele contains a small deletion (32 base pairs) that produces a shorter protein that HIV cannot use to infect T4 cells. As a result, people who are homozygous for this CC-CKR5 mutation are resistant to HIV infection.
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In the absence of retroviruses, eukaryotes may also undergo reverse transcription if which of the following is present?
A) Alu B) retrograde viruses C) retrotransposons D) prions E) none of the above
Intestinal protozoan infections are typically spread by
A. the respiratory route. B. blood transfusion. C. body fluids. D. the fecal-oral route.
In a human male, the saclike structure that contains the testes is the
A. epididymis. B. vas deferens. C. scrotum. D. sustentacular cells. E. seminal vesicle.
What is a good estimate of the background rate of species extinction?
A) one species per day B) one species per year C) one species per millennium D) one species per million years