Molecular Evolution

Question 1

What is natural selection?

Answer 1

The effects of a wide range of factors on the frequency of heritable changes in a species

Question 2

What is fitness?

Answer 2

How well a species is able to reproduce in its environment anything that increases fitness is selected for, and anything that decreases it is selected against

Question 3

How does selection affect the frequencies of genetic variants?

Answer 3

Genetic variants that confer a positive advantage will be selected for and vice versa, e.g. resistance to disease Conserved parts of the genome are resistant to change

Question 4

How does mutation affect the frequencies of genetic variants?

Answer 4

We all carry large numbers of genomic variants and their frequency will depend on selection and when they first arose

Question 5

How does migration affect the frequencies of genetic variants?

Answer 5

The physical movement of people from a different population results in new pools of variants being introduced to an existing population (admixture), which can be the only reason for change

Question 6

How does genetic drift affect the frequencies of genetic variants?

Answer 6

The frequency of a variant changes in a population due to chance. This is aided by mechanisms such as recombination

Question 7

Explain how sequence conservation works?

Answer 7

DNA sequence that is vital to the survival of an organism does not show much evidence of variation, most variants will be selected against as they have a deleterious effect. There is some flexibility for variation in the third base of codons as some amino acids are encoded by multiple codons

Question 8

Which areas of the genome are highly conserved?

Answer 8

Coding regions (Exons)

Question 9

Which areas of the genome are intermediately conserved?

Answer 9

Promoter, 5’ UTR, 3’ UTR, terminator

Question 10

Which areas of the genome are lowly conserved?

Answer 10

Introns, 3rd base of codons, terminator

Question 11

What is phylogenetics?

Answer 11

The study of evolutionary relationships

Question 12

How do phylogenetic trees work?

Answer 12

Distance between two entities on a tree is usually related to how similar they are - affected by evolutionary pressures and to time Time is estimated by measuring mutation rates

Question 13

How did we prove DCR polio vaccines did not cause HIV?

Answer 13

Came up with a phylogenetic tree of all the samples they could get a hold of, which showed that the SIV genome in the DCR wild chimpanzees was completely distinct from all known HIV genomes, so other strains were the source of the original transfer

Question 14

What is gene duplication?

Answer 14

This is duplication of a DNA sequence containing a gene, usually during unequal crossing over in meiosis Once it mutates, one copy continues the original function, whereas the other can evolve new functions by changes in the coding and/or control sequences

Question 15

What are the globin genes?

Answer 15

1) Alpha-like Found on chromosome 16 - 4 genes and 3 pseudogenes 2) Beta-like Found on chromosome 11 - 5 genes and 1 pseudogene

Question 16

What is a pseudogene?

Answer 16

A section of a chromosome that is an imperfect copy of a functional gene - they usually have many mutations - are non-functional - complicate PCR/sequencing

Question 17

Why do the symptoms of sickle cell disease begin at 5/6 months?

Answer 17

You do not have HbA until that age

Question 18

What causes sickle cell anaemia?

Answer 18

A single base change in the beta-globin gene of haemoglobin A, known as haemoglobin S Codon changes from GAG -> GTG, so Glu -> Val at position 7 of the protein Autosomal recessive disease, so if both parents have one copy of HbS then each child has a 1 in 4 chance of having sickle cell anaemia

Question 19

Why is sickle cell anaemia more common in countries in Africa/the middle East/India?

Answer 19

One copy of the HbS variant confers resistance to severe malaria, this heterozygote advantage means that the variant is maintained in the populations affected by malaria when otherwise they would be selected against and lost