Discuss how a genetic variant may explain why HIV infection rates are highest in sub-Saharan Africa. What will be an ideal response?
ANSWER: HIV infection is highest in sub-Saharan Africa. A 25-year study of this population involving
DNA samples from thousands of participants led to the discovery that an allele of the DARC
gene (MIM 613665), which encodes a cell surface protein, protects carriers from malaria but
increases susceptibility to HIV infection by 40%. In other words, people who carry the antimalaria
allele of DARC have
a greater chance of contracting HIV if exposed to this virus. In addition to increasing risk of
HIV infection, this allele interferes with the immune system’s ability to fight early stages of
HIV infection. About 60% of African Americans carry this DARC allele and are therefore
more susceptible to HIV infection than the general population. Studies of other populations
have revealed that genes scattered across the human genome influence resistance and
susceptibility to HIV infection and the rate of progression to AIDS.
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The lac operator site within the lac operon is an example of which of the following?
A. cis-acting element B. para-acting element C. trans-acting element D. inter-acting element E. contra-acting element
Fate maps of C. elegans development reveal that all somatic cells of the adult are directly descended from ____
produced during early development.
a. two germ-line cells b. cells of the hypodermis c. five somatic founder cells d. three endodermal cells e. five germ-line cells
The allele for albinism (c) is recessive to the allele for normal pigmentation (C). A normally pigmented woman whose
father is an albino marries an albino man whose parents are normal. They have three children, two normal and one albino. Give the genotypes for each person listed. What will be an ideal response?
Scientists believe that mitochondria may have evolved from bacteria because
a. they both have cristae membranes. b. mitochondria have their own DNA. c. the shapes and sizes are exactly the same. d. both are surrounded by a cell wall. e. both can live independently