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TLS Online TPP Program

#Question id: 12960

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.
Which of the following is most likely correct concerning the gene for resistance to warfarin? 

#Unit 10. Ecological Principles
  1. It is a wild-type gene induced to mutate by the direct action of warfarin.
  2. It is a mutation subsequently favoured by natural selection. 
  3. It is increased in frequency by virtue of its dominant status.
  4. It is carried by a bacterial plasmid vector.
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TLS Online TPP Program

#Question id: 1583

#Unit 4. Cell Communication and Cell Signaling

These cells are involved in cell-mediated immunity and destroy virally infected cells:
TLS Online TPP Program

#Question id: 1584

#Unit 4. Cell Communication and Cell Signaling

Which cell type interacts with both the humoral and cell-mediated immune pathways?
TLS Online TPP Program

#Question id: 16957

#Unit 4. Cell Communication and Cell Signaling

the immune system can be summarized as follows. Which is not correct for immune system?
TLS Online TPP Program

#Question id: 16956

#Unit 4. Cell Communication and Cell Signaling

Polyclonal antibodies are raised against bovine serum albumin in rabbit. Subsequently IgG in the antiserum is purified and digested with either pepsin or papain. Out of the following possibilities, which one is correct?
TLS Online TPP Program

#Question id: 16955

#Unit 4. Cell Communication and Cell Signaling

Stage thymocytes express neither CD4 nor CD8, markers associated with mature T cells. They are therefore called double negative (DN) cells. DN cells first travel to the region under the thymic capsule, a region referred to as the ________, where they proliferate and begin to generate their T-cell receptors. Thymocytes that successfully express TCRs begin to express both CD4 and CD8, becoming double positive (DP) cells, and populate the cortex, the site where most (85% or more) immature T cells are found.
TLS Online TPP Program

#Question id: 16954

#Unit 4. Cell Communication and Cell Signaling

match the following

 

 

A. endosteal niche

1. versatile cells that both generate bone and control the differentiation of HSCs

B. osteoblasts

2. line the blood vessels and also regulate HSC differentiation

C. reticular cells

3. send processes connecting cells to bone and blood vessels, and, unexpectedly

D. sympathetic neurons

4. can control the release of hematopoietic cells from the bone marrow.