Genes and Populations Flashcards
the Hardy-Weinberg assumptions?
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
the Hardy-Weinberg equations describe an …
…ideal scenario
How do individuals choose who to mate with?
- At random
- Assortative mating
A possible driver of speciation via natural selection is…
…assortative mating
Why are some populations get driven apart from mating?
when they are no longer physically together when mate choice is decided
Entire populations can be subdivided by…
…geographical barriers
There is..
…gene flow between populations
What is gene flow sometimes also known as?
rate of migration
if migration is large enough it will …
…act to counterbalance differences in allele frequencies of different populations
- in effect they become one population
the persistence of a mutation and the spread of an allele through a population depends on …
…whether the mutation has a deleterious or advantageous effect and whether it is dominant or recessive
most mutations will be…
most mutations will be deleterious
What are recessive lethals?
Chance effects
why is the population being of infinite size an important assumption of the HW equations?
This is known as genetic drift – the effect of chance. Random chance.
the larger the population the less chance has an effect
A severe drop in population size can cause…
…the bottleneck effect
WHen a population passes through a bottle neck…
…its size is reduced.
define monoallelic
one allele
Natural selection disrupts…
…HW equilibrium
natural selection affects…
allele frequencies
What affects allele frequencies?
- Bottleneck effects
- Founder effects
- Natural selection
- Mutation
- Population size
- Migration
- Assortative mating
what kind of mutation might be behind lactose tolerance? is this likely to be dominant or recessive?
Promoter mutated. Promoter changes shape so that transcription factor cannot bind. Lactase cannot turn on, hence lactose intolerance. A dominant mutation.
What mutation in which gene is responsible for the presence of dry earwax?
- a mutation in the ABCC11 gene
What does mutated gene ABCC11 encode?
it encodes a transporter protein sitting in the plasma membrane – involved in secretion
What does mutated gene ABCC11 effect?
effects the production of cerumen but.. also the mutation reduces axillary sweating – hence is advantageous in northern latitudes
sometimes it is not allele frequency that can be manipulated by natural selection but …
…genotype frequency
- the classic example is sickle cell anaemia
What causes sickle cell anaemia?
caused by a point mutation in the gene that encodes the β-globin chain of haemoglobin (Hbβ)
What type of disorder is sickle cell anaemia?
an inherited disorder.
What does mutation of Hbβ result in?
- mutation results in the replacement of negatively charged glutamate by
a neutral, hydrophobic valine - this change produces sticky patches on the protein surface
what is mutant haemoglobin gene?
HbS
mutant haemoglobin (HbS) polymerizes into …
…fibres, which distort red blood cells
Why does sickle cell anaemia cause pain?
blockage of the circulation, resulting in acute, severe pain
in some regions the sickle-cell allele can
reach frequencies as high as …
…15-20%
Advantage of sickle cell anaemia?
- heterozygote advantage – protection against malaria
WHats the most common adult form of haemoglobin ?
haemoglobin A
Sickle cell anaemia is the result of…
…mutation in the beta subunits (green)
haemoglobin will polymerise in …
…low oxygen conditions – rbc shape - long rigid
the examples we see in Mendel are chosen by …
…artificial selection
What causes sickle cell anaemia?
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.
Why does sickle cell anaemia persist?
Glutamate binds to valine causing a change in shape/structure. Changes the way the surface of the cell reacts.
We can use data from Hardy Weinberg equation to…
…quantify relative fitness (w) of genotypes in this case
What value do we use as the fittest value?
we use the top value as the fittest value
