Spherocytosis is an inherited blood disease in whichthe erythrocytes (red blood cells) are spherical insteadof biconcave. This condition can be inherited in adominant fashion, with ANK1 (the nonfunctional mutant allele) dominant to ANK1+. In people with spherocytosis, the spleen recognizes the spherical redblood cells as defective and removes them from thebloodstream, leading to anemia. The spleen in different people removes the spherical erythrocytes withdifferent efficiencies. Some people with sphericalerythrocytes suffer severe anemia and some mild anemia, yet others have spleens that function so poorly nosymptoms of anemia exist at all. When 2400 peoplewith the genotype ANK1 ANK1+ were examined, itwas found that all of them had spherical erythrocytes,2250 had anemia of varying severity, and 150 had nosymptoms. (Assume that ANK1 ANK1 homozygotesdo not exist.)a. Does this description of people with spherocytosisrepresent incomplete penetrance, variable expressivity, or both? Explain your answer. Can you derive any values from the numerical data to measurepenetrance or expressivity?b. Suggest a treatment for spherocytosis and describehow the incomplete penetrance and/or variableexpressivity of the condition might affect thistreatment.
Spherocytosis is an inherited blood disease in which
the erythrocytes (red blood cells) are spherical instead
of biconcave. This condition can be inherited in a
dominant fashion, with ANK1 (the nonfunctional mutant allele) dominant to ANK1+. In people with spherocytosis, the spleen recognizes the spherical red
blood cells as defective and removes them from the
bloodstream, leading to anemia. The spleen in different people removes the spherical erythrocytes with
different efficiencies. Some people with spherical
erythrocytes suffer severe anemia and some mild anemia, yet others have spleens that function so poorly no
symptoms of anemia exist at all. When 2400 people
with the genotype ANK1 ANK1+ were examined, it
was found that all of them had spherical erythrocytes,
2250 had anemia of varying severity, and 150 had no
symptoms. (Assume that ANK1 ANK1 homozygotes
do not exist.)
a. Does this description of people with spherocytosis
represent incomplete penetrance, variable expressivity, or both? Explain your answer. Can you derive any values from the numerical data to measure
penetrance or expressivity?
b. Suggest a treatment for spherocytosis and describe
how the incomplete penetrance and/or variable
expressivity of the condition might affect this
treatment.
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