Population genetics

Question 1

What is population genetics

Answer 1

The study of the genetic composition of biological groups

Question 2

How do changes in genetic composition occur? (7 points)

Answer 2

Natural selection
genetic drift
mutation
gene flow
mating structure
recombination
population size

Question 3

Population genetics is applicable to:

Answer 3

Evolutionary biology
disease inheritance
conservation biology
ecology

Question 4

Why is genetic diversity needed?

Answer 4

Allows for adaptation to environmental change
lessen the chances of inbreeding which can create and lock degenerative genetic traits into a population (Bulldogs and respiratory problems due to malformed facial features)

Question 5

What is used as a marker for genetic diversity?

Answer 5

Mitochondrial DNA (mtDNA)

Question 6

9 properties of mtDNA

Answer 6

– relatively small circular molecule
– ~16,000 bases in vertebrates
– it is haploid
– it is maternally inherited
– no recombination
– typically a higher mutation rate than nucleic DNA
– several thousand copies per cell
– no introns
– relatively few duplications

Question 7

4 major evolutionary forces

Answer 7

Mutation ( + diversity)
Migration ( + diversity)
Selection ( +/- Diversity)
Drift ( - diversity)

Question 8

Microsatellites

Answer 8

• Usually polymorphic even in small populations and endangered species
High polymorphism results from a high
mutation rate.
• Microsatellite mutation usually results in a
change in repeat number (an increase or
decrease of one repeat unit).
• Stepwise mutation model (SMM)

Question 9

Basic measures of genetic diversity microsatellites

Answer 9

• Proportion of polymorphic loci
– P= # polymorphic loci/ total # loci
e.g. # polymorphic loci = 4, total # loci = 5
P = 4/5 = 0.8
• Average number of alleles
– A =Total number of alleles for all loci/total # loci
e.g. sum total alleles all loci = 2+3+3+5+5 = 18, total # loci = 5
A = 18/5 = 3.6
• Heterozygosity
– H = sum % heterozygous in each locus/total # loci
e.g. % hetero = (1/10) + (4/10) + (3/10) + (10/10) + (8/10) =
2.6, total # loci = 5
H = 2.6/5 = 0.52

Question 10

Allele frequency

Answer 10

Proportion of genes in a population which are a given allele

Question 11

Locus

Answer 11

A site on a chromosome occupied by a gene

Question 12

Genotype

Answer 12

set of genes possessed by an individual; often specifically referring to a set of alleles at a particular locus

Question 13

Genotype frequency

Answer 13

Proportion of a population possessing a particular genotype.

Question 14

Hetrozygous

Answer 14

Possessing different alleles at focus (Aa)

Question 15

Homozygous

Answer 15

Possessing the same allele at a locus (AA)

Question 16

Hardy-Weinburg Equilibrium

Answer 16

If individuals in a population mate randomly, then genotypes carried in gametes are united randomly and genes are therefore also united randomly…
…the probability that a particular gamete carries a particular allele is the frequency of the allele in the population

Question 17

Hardy-Weinburg Formulae

Answer 17

p2 + 2pq + q2 = 1
After one generation of random mating
the genotype and allele frequencies will
remain at these frequencies in perpetuity
in the absence of other forces

Question 18

Assumptions of the H-W Equilibrium

Answer 18

• Mating is random
• The population is infinitely large
• No migration
• No mutation
• Equal probability of survival and
reproduction – no selection

Question 19

Why is HWE used?

Answer 19

• Acts as a null basis to examine the occurrence of other phenomena
• We can detect departures from HWE due to:
- natural selection
- genetic drift
- non-random mating
- inbreeding

Question 20

Genetic Drift

Answer 20

variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce.

Question 21

Consequences of Genetic Drift

Answer 21

• Random changes in allele frequency (their direction is neutral)
• Loss of genetic diversity – fixation of alleles
• Diversification of populations that are isolated
• Heterozygosity decays.
• This decay is proportional to the initial
population size
• Genetic drift is weak in large populations

Question 22

Migration

Answer 22

• Counteracts drift
• Changes allele frequencies
• Introduces new variation into populations
• Homogenizes variation between populations

Question 23

Bottlenecks

Answer 23

A population reduced to a small size - the Amur tiger was reduced to a population of 50 by 1947 but by 2009 that number increased to around 900. Yet the effective population was only 27 - 35 individuals

Question 24

Effective population

Answer 24

the number of individuals in a population who contribute offspring to the next generation.

Question 25

Inbreeding

Answer 25

When mating occurs between individuals that are genetically related (mother to son, father to daughter, first cousins etc) it increases the chance of disadvantages mutations. As inbreeding continues these mutation can become fixed in the population.

Question 26

Inbreeding depression

Answer 26

the reduced biological fitness in a given population as a result of inbreeding, or breeding of related individuals.

Question 27

Causes of inbreeding depression

Answer 27

• Deleterious mutations are usually partially
recessive
• Inbreeding increases homozygosity
• Therefore deleterious recessive mutationsare expressed in a greater number of individuals