Reading 20

Question 1

Define homologous genes.

Answer 1

-gene inherited in 2 species by a common ancestor

Question 2

What is a phylogenetic tree?

Answer 2

-depicts the evolutionary relationships among different organisms

Question 3

The last common ancestor of humans and mice lived a very long time ago, so many mutations have accumulated over time that make the human genome and the mouse genome very different from each other. Yet, there are many areas of highly conserved genome sequence between humans and mice. Why are some areas of the human genome and mouse genome so similar?

Answer 3

-because of purifying selection which eliminates individuals carrying mutations that interfere with important genetic functions

Question 4

Define purifying selection

Answer 4

-selection against deleterious variants

Question 5

What is the molecular clock hypothesis?

Answer 5

-the rate at which a protein evolves is roughly constant over time, the amount of molecular change that a protein has undergone can be used as a molecular clock to date evolutionary events

Question 6

Does the molecular clock run at the same speed for all sequences in the genome?

Answer 6

-no

Question 7

Give examples of genetic sequences that are unconstrained (not subject to purifying selection).

Answer 7

-intergenic regions
-portions of introns that lack splicing or regulatory signals
-genes that have been irreversibly inactivated by mutation

Question 8

Give examples of genetic sequences that are constrained (subject to purifying selection).

Answer 8

-amino acid sequences of proteins such as actin that engage in specific interactions with large numbers of other proteins and whose structure

Question 9

Many copies of Alu retrotransposons are present in both human and chimpanzee genomes. Are these Alu elements located in the same places in the human and chimpanzee genomes? Explain.

Answer 9

-more than 99% of the one million copies of the Alu family of retrotransposons that are present in both genomes are in corresponding positions

Question 10

What are synteny blocks?

Answer 10

-collection of contiguous genes located on the same chromosome

Question 11

Explain why gene duplications have been very important in evolution.

Answer 11

-many duplication events are likely to be followed by loss of function mutations in one or the other gene, it alters the genetic code