Biologists performed an experiment with flies to examine the effects of population size on the maintenance of genetic variation  and  on  egg-to-adult survival.  From  a  large  source  population, they  randomly  assigned  eggs  to  three experimental  populations  of  size  N,  equal  to  20,  60,  and0100.  For  later  generations,  they  collected  N  eggs  from each  population  and  moved  them  into  identical  vials  that  co0ntained  f2re0sh  me4d0ium.  Th6e0y  coun8te0d  the  number  of adult flies that emerged and used tissue samples from the adults for genetic analyses. Genetic variation was measured by  scoring  alleles  at  several  polymorphic  loci  and  expressed  as  the  average  number  of  alleles  at  those  loci.  The results are summarized in Figure 1 and Figure 2 below.

Based on Figure 1, which of the following best describes the change in genetic variation over time? 

#Question id: 2879

#Unit 2. Cellular Organization

Hybridization between mature mRNA and DNA can identify introns in eukaryotic genes. When mature mRNA produced by the insulin gene is hybridized with denatured chromosomal DNA, which of the following will most likely be observed?

#Question id: 2880

#Unit 2. Cellular Organization

According to the manner in which they work, three main classes of proteins that modify chromatin are recognized. Match the following classes of proteins given in COLUMN I with their respective examples in COLUMN II.

#Question id: 2881

#Unit 2. Cellular Organization

Depletion of a 2.2-kb noncoding RNA expressed from the HOXC locus by siRNA unexpectedly led to derepression of the HOXD locus on another chromosome encoding several Hox proteins and multiple other noncoding RNAs, in these cells. Assays similar to chromatin immunoprecipitation showed that this noncoding RNA, named HOTAIR, associates with the HOXD loci and with PRC2 complexes. This association results in

i. Histone H3K9 di- and trimethylation

ii. H2B monoubiquitinylation

iii. Histone H3K4 demethylation

iv. H2A monoubiquitinylation

v. Histone H3K4 methylation

vi. Histone H3K27 di- and trimethylation

Which of the following results is CORRECT regarding this association?

#Question id: 2882

#Unit 2. Cellular Organization

SUMO (small ubiquitin-related modifier) proteins are ∼10-kD polypeptides that function as reversible post-translational protein modifiers. They form isopeptide bonds with ɛ-amino groups of acceptor Lys residues in hundreds of target proteins in a process termed as sumoylation. Which of the following statements is correct regarding this modification?

#Question id: 2883

#Unit 2. Cellular Organization

Which, if any, of the following statements is incorrect?

I. In X-chromosome inactivation, the inactivated X chromosome is epigenetically silenced by a transcript, the XIST RNA, that is produced from the active X chromosome.

II. The XIST RNA works by coating most of the X chromosome that is to be inactivated and then recruiting Polycomb proteins to condense the chromosome.

III. The inactivated X chromosome carries the kinds of histone modification that are typical of heterochromatin.

IV. The pattern of X-chromosome inactivation is made randomly but once it has been established the same pattern of X-inactivation is propagated through all mitotic and meiotic cell divisions.

#Question id: 2884

#Unit 2. Cellular Organization

When the temperature of a solution of DNA is raised to near the boiling point of water, the optical density, (called absorbance) at 260 nm markedly increases, a phenomenon known as hyperchromicity. Which of the following statement is INCORRECT from the given set of statements?