Lecture 2 - Hardy Weinberg Equation

Question 1

What is Population Genetics

Answer 1

It is the understanding what evolutionary forces are at play that drive changes in allele and genotype frequencies

Question 2

What is the use of population Genetics

Answer 2

Fundamental to interpreting evolutionary history and understanding evolutionary forces

Also has practical applications to human genetics, animal/plant breeding and conservation

Question 3

allele

Answer 3

Genetic variants of a gene

Question 4

Genotype

Answer 4

The allelic composition of a gene, set of genes or even the whole genome

Question 5

Phenotype

Answer 5

The physical realisation of the genotype

Question 6

Gamete

Answer 6

Haploid product of meiosis in sex cells

Question 7

Zygote

Answer 7

diploid product of fertilisation

Question 8

Homozygote

Answer 8

Same allele at a locus

Question 9

Heterozygote

Answer 9

different allele at each locus

Question 10

Gene pool

Answer 10

the sum of alleles at all loci in a population

Question 11

Affect of gene pool on the next generation

Answer 11

The next generation is made up of a random selection of genes from the gene pool

Question 12

How is the gene pool an idealized concept

Answer 12

Unlikely that genes for the next generation are selected at random

For example it is more likely that an animal will mate with an individual in the same herd

Question 13

Polymorphism

Answer 13

More than one allele present at a single locus within a population of organisms

Question 14

What is the zero-force law of population genetics?

Answer 14

Hardy Weinberg equation

Question 15

How is the Hardy Weinberg equation a zero-force law?

Answer 15

As it measures what happens when there are no pressures on a population

Question 16

What is the hardy weinberg equation an application of?

Answer 16

An application of mendels laws on populations rather than individuals

Question 17

What is the Hardy-Weinberg equation?

Answer 17

p^2+2pq+q^2=1

p= the frequency of allele A
q= the frequency of allele of A1

where p>=0, q<=1 and p+q=1

Question 18

What are the assumptions of the hardy weinberg principle?

Answer 18

No mutations

No migration

Mating is Random

Population size is infinite

No natural selection

Question 19

Eggs and milt bucket experiment

Answer 19

A bucket of sperm and eggs

Can be studied as it is a real-life gene pool with random mating

Question 20

What does genotype frequencies depend upon?

Answer 20

Underlying allele frequency

Question 21

Hardy Weinberg Equilibrium

Answer 21

Principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors

Question 22

How to test for deviation from HWE

Answer 22

Compare the observed genotype frequencies and expected genotype frequencies

Then do an x-square test

Question 23

How can HWE be used to predict frequencies in gene carriers?

Answer 23

Most genes causing disease are recessive/dominant alleles which means that you cannot detect heterozygotes from homozygote dominant individuals

However if you use the HWE you know that the homozygote is q^2 and therefore can work out the frequencies of the other alleles and genotypes

Question 24

Importance of HWE

Answer 24

Proof that in absence of any evolutionary forces allele and genotype frequencies remain constant over time

Explains why genotype frequencies rarely deviate from HWE expectations

Can be used to predict frequency of disease carriers

Example of a basic population genetics model

Null hypothesis that can be rejected and prove that evolution occurs

Question 25

Assortative mating

Answer 25

Choice of mates is based on phenotype

Question 26

Inbreeding

Answer 26

Mating of genetically-related individuals

Question 27

What does non-random mating influence

Answer 27

genotype frequencies but not allele frequencies

Question 28

Positive Assortative mating

Answer 28

Like mates with like

For example tall people mating with each other

Question 29

Negative assortative mating

Answer 29

Opposites attract

Question 30

Affects of positive assortative mating?

Answer 30

Increases the number of homozygotes

May lead to speciation

Question 31

Affects of negative assortative mating

Answer 31

Decreases the number of homozygotes

Question 32

What does assortative mating effect?

Answer 32

Does not affect all loci on the genome, only loci in the genome encoding the phenotype

Question 33

Example of positive assortative mating

Answer 33

Burmeistera

Bats are very efficient at moving pollen between wide flowers whereas hummingbirds are efficient at pollen transfer between narrow flowers

Intermediate forms are less fit and will favour specialisation which eventually leads to speciation

Question 34

Example of negative assortative mating

Answer 34

Alpine Woodsorrel

They are monoecious (male and female parts on the same flower)

There are two different forms: one with the stamen above the style (thrum) and one with the style above the stamen (pin)

Foraging insects collect pollen on different parts of its body depending on which form of flower it is. The insect can then only deposit the pollen on the oposite type of plant due to where it is on its body

Prevents self fertlisation

Question 35

Inbreeding

Answer 35

Occurs when genetically related individuals mate

Question 36

What part of the genome does inbreeding affect?

Answer 36

All loci

Question 37

Inbreeding coefficient

Answer 37

The probability that two alleles in an individual are identical by descent

Closer to 1 indicates inbreeding

Question 38

Effects of random mating on the inbreeding coefficient

Answer 38

F=0

Question 39

Effects of partial inbreeding

Answer 39

0<F<1

increase in homozygotes and decrease in heterozygotes relative to HWE

Question 40

Inbreeding depression

Answer 40

Reduction in mean population fitness due to inbreeding

Question 41

How does inbreeding cause a loss of fitness?

Answer 41

Most new mutations are recessive and deleterious

They can occur at low frequencies before the cause a reduction in fitness

With inbreeding more homozygotes are created exposing deleterious recessive alleles for selection

Question 42

Example of inbreeding in animals

Answer 42

Pedigree dogs

Loss of fitness

Question 43

Example of inbreeding in humans?

Answer 43

Royal families used to have a large amount of inbreeding leading to genetic defects

Such as Hapsberg Jaw