Week 4

Question 1

What is a population?

Answer 1

group of organisms of the same species living in the same geographical area

Question 2

What is population genetics?

Answer 2

application of genetic principles to entire populations of organisms

Question 3

What is an allele?

Answer 3

One of the alternative forms (different nucleotides) of a gene.

Question 4

When we talk about alleles in population genetics, what are we mostly concerned with?

Answer 4

the frequencies of alleles in a population.

Question 5

What do allele frequencies measure?

Answer 5

• how common an allele is in a population
• they can be calculated for each allele in a gene pool.

Question 6

Where is genetic variation stored?

Answer 6

• in a population’s gene pool.
• made up of alleles and allele combinations form when organisms have offspring

Question 7

What does genetic variation lead to?

Answer 7

• Phenotypic variation

Question 8

What is phenotypic variation necessary for?

Answer 8

• natural selection.

Question 9

What is the basis of evolution?

Answer 9

• Changes in allele frequencies within or between populations
• selection, mutation, genetic drift, gene flow

Question 10

What are the four main processes that cause changes in allele frequencies (genetic variation)?

Answer 10

• selection, mutation, genetic drift, gene flow.

Question 11

What is the proximate mechanism for evolution?

Answer 11

• allele frequency changes

Question 12

What are the four main components of natural selection?

Answer 12

• inheritance ( traits controlled by genes)
• variation (genetic variation between individuals)
• survival of the fittest (not all individuals mate)
• differential survival and reproduction

Question 13

What does natural selection occur in response to?

Answer 13

• environmental pressures

Question 14

Individuals do not evolve, ________ do

Answer 14

• populations do.

Question 15

What is evolution measured as?

Answer 15

• change in relative proportions of heritable variations in a population over several generations.

Question 16

Why is genetic variation important for evolution?

Answer 16

• genetic variation leads to phenotypic variation, which is required for natural selection.

Question 17

What does natural selection cause happen in a population?

Answer 17

• different environmental pressures between populations so:
• greater between-population genetic variation but
• lower within-population genetic variation.
• sometimes resulting in new species.

Question 18

What is a mutation?

Answer 18

• a random change in the nucleotides of a gene.

Question 19

What is the ultimate source of genetic variation? How?

Answer 19

• mutation
• it increases genetic variation when it creates new alleles

Question 20

What are the types of mutation?

Answer 20

• point mutations

Question 21

What are point mutations? When can it change a phenotype?

Answer 21

• single base pair change in genome
• in a coding region

Question 22

How can a point mutation be passed to offspring?

Answer 22

• if it happens during gamete mutation it can be passed on to offspring

Question 23

What is genetic drift?

Answer 23

• a change in allele frequencies caused by random sampling of alleles over generations.
• completely random sampling.
• some individuals not surviving randomly and loss of alleles.
• random fluctuations

Question 24

Where does genetic drift act more quickly?

Answer 24

• smaller populations
• can reduce variation in these populations through the loss of alleles.

Question 25

What is fixation?

Answer 25

- in genetic drift where an allele becomes the only allele because all others have been removed.

Question 26

Where does genetic drift usually happen?

Answer 26

- founder effects (as well as bottlenecks) - reduced genetic variation from original population - a different sample of the genes in the original population.

Question 27

What is gene flow? When does this occur?

Answer 27

- the transfer of alleles from one population to another - when individuals join new populations AND REPRODUCE

Question 28

What does high gene flow do?

Answer 28

- keeps neighbouring populations similar and can maintain genetic variation within populations

Question 29

What does low gene flow do?

Answer 29

- increases the chance that two populations will evolve into two different species and can lead to lower within-population genetic variation through inbreeding.

Question 30

If an individual is inbred:

Answer 30

- has low heterozygosity

Question 31

If high heterozygosity?

Answer 31

- high genetic variation.

Question 32

Genetic drift and low gene flow over time produce a march towards

Answer 32

- homozygosity

Question 33

What is the Hardy-Weinberg equilibrium model? What does it explain?

Answer 33

- a framework for understanding how populations evolve. - explains how Mendelian segregation influences allelic and genotypic frequencies in a population

Question 34

What does HWE describe? What are the 5 assumptions of hardy weinberg equilibrium?

Answer 34

- populations that are not evolving 1. no natural selection 2. No mutation 3. No migration (gene flow) 4. Infinitely large population (to avoid genetic drift) Mating is random

Question 35

What does the HWE predict? What can we then do with those?

Answer 35

- genotype frequencies in a population - compare those with actual frequencies from populations - used with simple mendelian inheritance (two alleles)

Question 36

Describe HWE equation:

Answer 36

p + q = 1 Then p2 + 2pq + q2 = 1

Question 37

If HWE assumptions are met, population will be in________

Answer 37

- genetic equilibrium AKA hardy-weinberg equilibrium

Question 38

What are the two predictions of HWE?

Answer 38

- allele frequencies do not change over generations - after on generation of random mating, genotypic frequencies will remain in the following proportions:

Question 39

How do you do HWE with two numbers (allele counts)?

Answer 39

- first assign alleles - prepare a punnet square of allele combinations - we calculate the frequency of q2 because we know their alelle frequencies (both recessive - we don’t know this about p). Q2 = 12/(988+12) = 0.012 - calculate the frequency of q of the recessive blue allele (y) so q = 0.11 - we can minus that off 1 so p = 0.89 - then apply the formula to get the genotype frequencies.

Question 40

Why do we use HWE?

Answer 40

- it’s a good null hypothesis compared to values from a real population to describe statistically significant deviations from the equilibrium. If different, evolution is occuring - therefore either selection, mutation, or gene flow, or genetic drift is occuring to alter them. - these are occurring and violating the HW assumptions and constitutes a null model and is fundamental to the study of evolution.