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TLS Online TPP Program

#Question id: 13143

The Norway rat (Rattus Norvegicus), a widespread pest, was controlled for about a decade by the anticoagulant warfarin. This chemical substance, placed in food pellets, is absorbed by the intestinal tract and inhibits the clotting of blood. After a population decline for about 10 years, rat populations increased and stabilized. In one European population, as illustrated in the graph below, the percentage of rats resistant to warfarin has remained fairly stable over a number of years.

Resistance to warfarin is governed by a dominant autosomal gene, R. More than 15 percent of the resistant animals are heterozygous at this locus (Rr). The table below indicates the response to warfarin and relative reproductive fitness of individuals that are homozygous or heterozygous for the dominant gene (R). The RR individuals have a 20-fold increase in vitamin K requirement over individuals.

Fitness is a measure of the reproductive success of a particular genotype. The highest fitness is 1.00.
In a population where warfarin is no longer applied, the expectation is that the

#Unit 10. Ecological Principles
  1. Dominant gene (R) will supplant the recessive gene (r) in the population
  2. Heterozygotes (Rr) will have a reproductive advantage over both homozygotes (RR and rr) 
  3. Frequency of the dominant gene (R) will decline
  4. Frequency of recessive individuals will gradually decline
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TLS Online TPP Program

#Question id: 15528

#Unit 4. Cell Communication and Cell Signaling

The B7 family of protein interact  with distinct receptor present on the T-cells, 
TLS Online TPP Program

#Question id: 15527

#Unit 4. Cell Communication and Cell Signaling

CD4 and CD8 T cells leave the thymus and enter the circulation as resting cells in which stage of the cell cycle?
TLS Online TPP Program

#Question id: 15526

#Unit 4. Cell Communication and Cell Signaling

If a thymocyte randomly generated a TCR with an affinity for MHC Class I, the TCR and CD8 would bind MHC Class I together, and generate a signal that specifically initiated a program that is 
a) silenced CD8 expression
b) silenced CD4 expression
c) induced expression of genes specific for helper T-cell lineage function
d) induced expression of genes specific for cytotoxic T-cell lineage function
TLS Online TPP Program

#Question id: 15525

#Unit 4. Cell Communication and Cell Signaling

In the instructive model, TCR/CD4 and TCR/CD8 coengagement generates unique signals, if a thymocyte randomly generated a TCR with an affinity for MHC Class I. which thymocyte would bind with MHC class I?
TLS Online TPP Program

#Question id: 15524

#Unit 4. Cell Communication and Cell Signaling

The bulk of DP thymocyte death (~95%) occurs among thymocytes that fail positive selection because 
TLS Online TPP Program

#Question id: 15523

#Unit 4. Cell Communication and Cell Signaling

The appearance of ϒδ thymocytes and αβ thymocytes during mouse fetal development. Fetal animals generate
a) more αβ T-cells than ϒδ T-cells
b) the proportion of ϒδ T-cells generated drops off dramatically after birth
c) the proportion of αβ T-cells generated drops off dramatically after birth
d) more ϒδ T-cells than αβ T cells