Molecular evolution

Question 1

What is ‘on the origin of species’ about?

Answer 1

Theory to explain the current variety of life on earth

Question 2

What are the two main concepts in ‘the origin of species’?

Answer 2

Natural selection and fitness

Question 3

What is the definition of natural selection?

Answer 3

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

Question 4

What is the definition of fitness?

Answer 4

How well a species is able to reproduce in its environment

Question 5

What is the relationship between fitness ad selection?

Answer 5

→ Anything that increases fitness is selected for
→ anything that decreases fitness is selected against

Question 6

What happens to neutral changes?

Answer 6

They vary randomly

Question 7

What is modern synthesis?

Answer 7

Unifying evolution with genetics to explain the molecular processes underlying evolution

Question 8

What is the main source of heritable variation in a species?

Answer 8

Genetic variation

Question 9

What 4 things are the frequency of genetic variants affected by?

Answer 9

→ Selection
→ Mutation
→ Migration
→ Genetic drift

Question 10

What types of genetic variants are selected for?

Answer 10

Variants that confer a positive advantage

Question 11

What is an example of a positive advantage?

Answer 11

→ resistance to disease
→ an ability to metabolise a new food source
→ change in appearance to enhance mate choice

Question 12

What parts of the genomes are resistant to change and why?

Answer 12

→ They are conserved
→ because they contain vital sequences

Question 13

What is mutation?

Answer 13

Process by which variation arises

Question 14

What does genomic variant frequency depend on?

Answer 14

→ Selection
→ When the variants first occurred

Question 15

What are the three possibilities of low frequency in a rare variant?

Answer 15

→ May have arisen recently
→ be deleterious and being selected against

→ both

Question 16

What is migration and what does this result in genetically and what is this called?

Answer 16

→ Physical movement from a different population
→ Result in new pools of variants being introduced to an existing population

→ Admixture

Question 17

Why does admixture need to be taken into account when studying populations?

Answer 17

Population frequencies of specific variants can change purely due to admixture and not be disease related

Question 18

What is genetic drift?

Answer 18

How the frequency of a variant changes in a population due to chance

Question 19

What are 2 reasons that variation is not passed on?

Answer 19

→ Not all organisms will pass on their genetic variants
→ mechanisms such as recombination will also result in not all variants being passed on

Question 20

What are all variants subject to?

Answer 20

Genetic drift

Question 21

What types of sequences don’t show variation?

Answer 21

DNA sequences that is vital to the survival of an organism

Question 22

What happens if variants occur in conserved regions?

Answer 22

They will be selected against as they are likely to have a strong deleterious effect

Question 23

Why is there some flexibility in variation in conserved regions?

Answer 23

there is flexibility in the third base of codons as some amino acids are encoded by multiple codons

Question 24

Where is high conservation seen and what is the exception?

Answer 24

→ Coding regions
→ but not in exons as they have non coding regions
→The further you move on the tree from us, the less introns we have in common with them

Question 25

Where is intermediate conservation seen?

Answer 25

→ promoter → 5' UTR → Splicing sites → 3' UTR → Terminator

Question 26

Where is low conservation seen?

Answer 26

→ Introns → 3rd base of codons → Terminator (vague signals such as GC rich regions)

Question 27

What can be used to generate an evolutionary profile and why?

Answer 27

→ Cross species comparison → To see how genes change over time

Question 28

What is phylogenetics?

Answer 28

Working out the history of the genome

Question 29

What is needed for phylogenetic sequencing?

Answer 29

→ Observe sequences → See how are they related

Question 30

What does a phylogenetic tree show?

Answer 30

Illustrate relatedness of different species

Question 31

What does distance show on a phylogenetic tree?

Answer 31

→ The more distance the less related they are → distance is related to both evolutionary pressures and time

Question 32

How is time estimated on phylogenetic trees?

Answer 32

Measuring mutation rates

Question 33

What is the theory behind the introduction of HIV to the human population?

Answer 33

→ a contaminated polio vaccine → some polio vaccines were produced with cultured chimpanzee cells which could have been infected with SIV

Question 34

What is gene duplication?

Answer 34

Duplication of a DNA sequence containing a gene, can be multiple genes

Question 35

What is the typical mechanism of gene duplication?

Answer 35

Unequal crossing over

Question 36

What are the two options after duplication?

Answer 36

→ One copy can continue the original function → the other copy can evolve new functions by changes in the coding or control sequences →Means possibilities of related genes arising that allows better adaptation.

Question 37

What is unequal crossing over?

Answer 37

→ Recombination between sequences that are not the correct sequence but are very similar → often low copy number repeat sequences

Question 38

When does unequal crossing over usually happen?

Answer 38

Often low copy number repeat sequences

Question 39

How many clusters of the globin gene are there?

Answer 39

2

Question 40

Where are the alpha like globin genes?

Answer 40

→ chromosome 16 → 3 genes → 3 pseudogenes

Question 41

Where are the beta like globin genes?

Answer 41

→ chromosomes 11 → 5 genes and one pseudo gene

Question 42

How are the globin genes arranged?

Answer 42

In order of expression during development

Question 43

What are the 3 types of Hb?

Answer 43

→ Embryonic → Fetal → Postnatal

Question 44

What is the control region of the beta globin cluster?

Answer 44

Beta LCR (locus control region)

Question 45

How have globin genes evolved?

Answer 45

Divergence

Question 46

What are pseudogenes?

Answer 46

Non functioning genes

Question 47

What allows the expression of globin genes at different stages?

Answer 47

Divergence of promoters has occurred so they bind different transcription factors and allow expression of genes at different stages of development

Question 48

What is fetal Hb made from?

Answer 48

Alpha and gamma subunits

Question 49

What is adult Hb made from?

Answer 49

Alpha and beta subunits

Question 50

How are pseudogenes formed?

Answer 50

After gene duplication one gene maintains original function and the other diverges

Question 51

What do pseudogenes contain?

Answer 51

Many mutations and are non functional

Question 52

When do sickle cell symptoms start and why?

Answer 52

→ 5- 6 months → change between HbF and HbA

Question 53

What are the symptoms of sickle cell?

Answer 53

→ Anaemia → Acute pain episodes - crises - due to oxygen deprivation → Increased infection → stroke, hypertension

Question 54

What are the symptoms due to?

Answer 54

Sickling of red blood cells

Question 55

How does sickle cell occur?

Answer 55

A single base change in the beta globin gene of HbA

Question 56

What is the codon change in sickle cell?

Answer 56

→ GAG to GTG → Glutamine to valine at position 6

Question 57

What kind of a disease is sickle cell?

Answer 57

Autosomal recessive

Question 58

What is the chance of a child getting SCD if the parents have 1 copy each?

Answer 58

1 in 4

Question 59

What is the distribution of HbS?

Answer 59

→ Africa → Middle east → India

Question 60

Why has sickle cell not been selected against?

Answer 60

→ with one copy of HbS it improves reproductive fitness → because it confers resistance to severe malaria

Question 61

What does heterozygote advantage mean for HbS?

Answer 61

The variant is maintained because of the huge selection pressure