Evolution Lecture 3

Question 1

How many genes do animals and plants have in their genome?

Answer 1

Tens of thousands

Question 2

Locus

Answer 2

Where the two alleles are.

Question 3

Population

Answer 3

Localised group of interbreeding and interacting individuals (sexual species). Each species is made up of one to many populations (that can interbreed when
they meet). Members of on population is more closely related than a different population. Typically they are separated by distance.

Question 4

Who are species in a population move likely to breed with?

Answer 4

Other people in the population, but occasionally won’t (interbreeding). Typically the frequency of the alleles between the populations are different.

Question 5

Gene Pool

Answer 5

All alleles at all gene loci in all individuals. Shows the total genetic variability or potential in a population.

Question 6

Fixed alleles

Answer 6

Whole population is homozygous at locus.

Question 7

Polymorphic loci

Answer 7

2+ alleles in population, each present at some frequency. They can be present equally or one is rare and one is common. Most populations have
thousands of polymorphic loci. This is where we have genetic variation and where natural selection happens.

Question 8

Source of genetic variation?

Answer 8

Mutation and gene duplication.

Question 9

Mutations

Answer 9

New alleles arise by mutation in existing alleles.
(A single mutation can result in a new allele). This is a change in a base pair.

Question 10

How can mutations impact the environment?

Answer 10

Most mutations don’t meaningfully affect fitness
a ‘neutral variation’ (neutral alleles). It doesn’t matter if you have the mutation or not. The most it could do is change the phenotype.

Some reduce fitness: harmful alleles (a.k.a. ‘deleterious’ mutations/alleles). Because organisms reflect many generations of past selection, their phenotypes are ones best suited for there environment, so most new mutations are at least slightly harmful.

*A very few increase fitness: beneficial alleles. These are the least likely to occur (eg. warfarin rats)

Question 11

In animals what happens to. the mutations?

Answer 11

They mostly occur in somatic called and aren’t passed on to the offspring.

Question 12

Why does HIV get more mutations?

Answer 12

It has an RNA genome which causes more mutations because it lacks a RNA repair mechanism in host cells. This means single drug treatments are unlikely to be effective against HIV, but a mix of medications is likely to work better.

Question 13

Gene Duplication

Answer 13

Duplication of smaller pieces of DNA may not be harmful, these can get passed on to generations, allowing mutations to accumulate. Resulting in an expanded genome with new genes that may take on new functions.

Question 14

How could gene flow be introduced?

Answer 14

By other population, which made the mutation.

Question 15

Microevolution

Answer 15

Change in the frequencies of alleles over generations. At the extreme, ‘change’ can mean fixation of an allele, or loss (extinction) of an allele. It’s evolution on a small scale.

Question 16

How to calculate genotype frequencies?

Answer 16

of individuals with the genotype / # of total organisms

Question 17

P and q in allele frequencies?

Answer 17

If possible p is dominant and q is recessive.

Question 18

Hardy-Weinberg Principle

Answer 18

Describes expected relationships between allele and genotype frequencies when there is no evolution under certain assumptions. If we compare what we calculated with what occurred and they are equal, this suggests the population isn’t evolving. In populations that are not evolving, allele and genotype frequencies will remain constant from each generation.

Question 19

What must occur for evolution to occur?

Answer 19

An individual must differ genetically, the presence of genetic variation does not guarantee that a population will evolve.

Question 20

Random mating

Answer 20

Taking two random alleles out of the population pool, sticking them together to get the combination of alleles in any new individual in that population.

Question 21

The math Hardy-Weinberg Principle

Answer 21

p2 + 2pq + q2 = 1.
p2, q2 = Expected frequencies of the two homozygote genotypes
2pq = Expected frequency of heterozygotes

Question 22

Using Hardy-Weinberg principle?

Answer 22

1) Estimating allele and genotype frequencies. e.g. Prevalence of carriers (heterozygotes) of recessive genetic disorders. This is done by using just one of the frequency of one of the homozygous genotypes.

2) Populations with genotype frequencies that conform to the equation are said to be in Hardy-Weinberg equilibrium at that locus. Look at population genotype frequencies to see if they are actually in Hardy-Weinberg equilibrium

Question 23

Assumptions of Hardy-Weinberg

Answer 23

It’s how we can have population where the genotype and allele frequencies don’t correspond.
1)No net mutations
2) Random mating
3) No natural selection
4) Very large (infinite) population size
5) No migration (no loss or more coming in of a individuals from a population).
Violation of these assumptions usually signals evolutionary change

Question 24

Example of non-random mating?

Answer 24

How plants can be both mother and father. This is called stealthing, this leading to lower frequencies of heterozygotes.

Question 25

3 Causes of microevolution

Answer 25

Natural Selection (No natural selection)
Gene Flow (No migration)
Genetic Drift (Very large (infinite) population size)

Question 26

Which of the 3 causes result in adaptive evolution?

Answer 26

Natural selective

Question 27

Adaptive evolution

Answer 27

A change to fit an environment. Long term increase in suitably of organisms to their environment. Increase frequency of the better allele.

Question 28

Gene Flow

Answer 28

Dispersal of gametes (e.g. pollen) or migration. Gene flow from population with different allele frequencies = change in allele frequencies. Gene flow can introduce new alleles (and mutations) to a population. It can prevent some populations from fully adapting to local conditions, but it can also transfer allele that improve the ability of populations to adapt to local conditions.

Question 29

Example of gene flow?

Answer 29

The spread of pesticide resistance around the world, once the new gene is introduced natural selection occurs. Mating in humans is more common between members of different populations because of travel technology.

Question 30

Random Genetic Drift

Answer 30

‘Sampling error’: random changes in allele frequencies over generations. Can lead to fixation (or extinction) of alleles in population in the absence of natural selection. It’s in one population over time. Chance event cause allele frequencies to fluctuate unpredictably from generation to the next. Given enough time it’s gonna go fixed (1) or extinct (0), once this happens they can’t go back. Drunk Simpson on train tracks.

Question 31

How does drift depend on the population size?

Answer 31

Faster in small population than large for an allele to become fixed. Genetic drift takes over natural section in small populations.

Question 32

Randomness of genetic drift?

Answer 32

Neutral allele at frequency 0.5 is equally likely to eventually be fixed or to go extinct [In theory, chance of eventual fixation of a neutral allele is the same as its frequency]. If you had a frequency of 0.1 it’s way more likely to become extinct.

Question 33

Genetic bottlenecks

Answer 33

They typically occur in sudden changes of the environment (fires and floods) this causes a serve drop in population size. Causes diversity to decreases. Breeding population is very small for a time. Genetic drift powerful: allele frequencies change, many alleles fixed or go extinct. = Lower genetic diversity overall, even if population later expands in numbers. Some rare alleles can increase in frequency = high frequencies of harmful alleles possible (even fixation of slightly harmful alleles).

Question 34

The Greater Prairie Chickens of Illinois example?

Answer 34

Lower genetic variability than larger populations. Much reduced reproductive success (% eggs hatched) Fitness lowered by accumulated harmful alleles. They lived in Canadian and US prairies were converted to farmland and other uses the # of chicken plummeted. No more in Canada, but very very little in Illinois. Using DNA, estimated how much genetic variation was present before. Genetic drift increased frequency of harmful alleles leading to the low egg hatching rate. To counter this, neighbouring states birds were added to Illinois. Then the hatching rate improved to over 90%.

Question 35

How to stop endangered species/populations?

Answer 35

Genetic diversity (gene pool) can be increased by adding individuals from other populations. Captive breeding programs manage matings to preserve remaining genetic diversity.

Question 36

Founder Effect

Answer 36

It’s a special case of the bottleneck. It’s involves an ancestral population with a lot of genetic diversity. Then a few individuals found new population (possibly by few members are blown away by a storm onto a new island), then the new population grows which lowers genetic diversity. Some previously rare alleles end up being much more common in the new population (see yellow allele in previous slide). e.g. High prevalence of particular genetic diseases in isolated human populations.

Question 37

Example of founder effect?

Answer 37

Ellis- Van Creveld syndrome is way more common in the Amish because they breed with each other and have very many children.