Genes and Populations

Question 1

the Hardy-Weinberg assumptions?

Answer 1

1 – individuals in the population mate at random – there is no assortative mating

2 – no migration from other populations changes the allele frequency

3 – no new mutation in any genes arises

4 – population size is infinite and therefore there are no chance effects on allele frequency

5 – natural selection is not acting on any of the alleles

Question 2

the Hardy-Weinberg equations describe an …

Answer 2

…ideal scenario

Question 3

How do individuals choose who to mate with?

Answer 3

• At random
• Assortative mating

Question 4

A possible driver of speciation via natural selection is…

Answer 4

…assortative mating

Question 5

Why are some populations get driven apart from mating?

Answer 5

when they are no longer physically together when mate choice is decided

Question 6

Entire populations can be subdivided by…

Answer 6

…geographical barriers

Question 7

There is..

Answer 7

…gene flow between populations

Question 8

What is gene flow sometimes also known as?

Answer 8

rate of migration

Question 9

if migration is large enough it will …

Answer 9

…act to counterbalance differences in allele frequencies of different populations

• in effect they become one population

Question 10

the persistence of a mutation and the spread of an allele through a population depends on …

Answer 10

…whether the mutation has a deleterious or advantageous effect and whether it is dominant or recessive

Question 11

most mutations will be…

Answer 11

most mutations will be deleterious

Question 12

What are recessive lethals?

Answer 12

Chance effects

Question 13

why is the population being of infinite size an important assumption of the HW equations?

Answer 13

This is known as genetic drift – the effect of chance. Random chance.

the larger the population the less chance has an effect

Question 14

A severe drop in population size can cause…

Answer 14

…the bottleneck effect

Question 15

WHen a population passes through a bottle neck…

Answer 15

…its size is reduced.

Question 16

define monoallelic

Answer 16

one allele

Question 17

Natural selection disrupts…

Answer 17

…HW equilibrium

Question 18

natural selection affects…

Answer 18

allele frequencies

Question 19

What affects allele frequencies?

Answer 19

• Bottleneck effects
• Founder effects
• Natural selection
• Mutation
• Population size
• Migration
• Assortative mating

Question 20

what kind of mutation might be behind lactose tolerance? is this likely to be dominant or recessive?

Answer 20

Promoter mutated. Promoter changes shape so that transcription factor cannot bind. Lactase cannot turn on, hence lactose intolerance. A dominant mutation.

Question 21

What mutation in which gene is responsible for the presence of dry earwax?

Answer 21

• a mutation in the ABCC11 gene

Question 22

What does mutated gene ABCC11 encode?

Answer 22

it encodes a transporter protein sitting in the plasma membrane – involved in secretion

Question 23

What does mutated gene ABCC11 effect?

Answer 23

effects the production of cerumen but.. also the mutation reduces axillary sweating – hence is advantageous in northern latitudes

Question 24

sometimes it is not allele frequency that can be manipulated by natural selection but …

Answer 24

…genotype frequency

• the classic example is sickle cell anaemia

Question 25

What causes sickle cell anaemia?

Answer 25

caused by a point mutation in the gene that encodes the β-globin chain of haemoglobin (Hbβ)

Question 26

What type of disorder is sickle cell anaemia?

Answer 26

an inherited disorder.

Question 27

What does mutation of Hbβ result in?

Answer 27

• mutation results in the replacement of negatively charged glutamate by
  a neutral, hydrophobic valine
• this change produces sticky patches on the protein surface

Question 28

what is mutant haemoglobin gene?

Answer 28

HbS

Question 29

mutant haemoglobin (HbS) polymerizes into …

Answer 29

…fibres, which distort red blood cells

Question 30

Why does sickle cell anaemia cause pain?

Answer 30

blockage of the circulation, resulting in acute, severe pain

Question 31

in some regions the sickle-cell allele can
reach frequencies as high as …

Answer 31

…15-20%

Question 32

Advantage of sickle cell anaemia?

Answer 32

• heterozygote advantage – protection against malaria

Question 33

WHats the most common adult form of haemoglobin ?

Answer 33

haemoglobin A

Question 34

Sickle cell anaemia is the result of…

Answer 34

…mutation in the beta subunits (green)

Question 35

haemoglobin will polymerise in …

Answer 35

…low oxygen conditions – rbc shape - long rigid

Question 36

the examples we see in Mendel are chosen by …

Answer 36

…artificial selection

Question 37

What causes sickle cell anaemia?

Answer 37

alteration of the haemoglobin A gene by one amino acid causes change in the function of the protein – valine at position 6 causes hydrophobic collapse and the molecules can form polymers resulting in sickle-shaped red blood cells.

Question 38

Why does sickle cell anaemia persist?

Answer 38

Glutamate binds to valine causing a change in shape/structure. Changes the way the surface of the cell reacts.

Question 39

We can use data from Hardy Weinberg equation to…

Answer 39

…quantify relative fitness (w) of genotypes in this case

Question 40

What value do we use as the fittest value?

Answer 40

we use the top value as the fittest value