1.06 Population Genetics

Question 1

What is a Genetic Locus?

Answer 1

A locus is the specific location of a gene or DNA sequence or position on a chromosome

Question 2

What five factors influence allele frequencies?

Answer 2

Natural Selection
Sexual Selection
Mutations
Genetic Drift
Gene Flow

Question 3

Describe: Natural Selection

Answer 3

Alleles for more fitter organisms become selected

Question 4

Describe: Sexual Selection

Answer 4

Alleles for more sexually attractive organisms become more frequent

Question 5

Describe: Mutations

Answer 5

New alleles appear due to mistakes in the DNA

Question 6

Describe: Genetic Drift

Answer 6

Changes in allele frequency due to random chance

Question 7

Describe: Gene Flow

Answer 7

Changes in allele frequency due to mixing of a new population

Question 8

Describe and state the Hardy-Weinberg Equilibrium

Answer 8

p^2 + 2pq + q^2 = 1 or p + q = 1
The formulation states a simple relationship between frequency of alleles at a genetic locus and the genotypes resulting from those alleles.

Question 9

What is the fixation index?

Answer 9

It is a measure of how populations differ genetically. A measure of genetic distance. It is a measure of the difference in allele frequency between two populations. Can theoretically range from 0.0 (no genetic difference) to 1.0 (complete genetic difference)

Question 10

Identify and name all the elements in the Hardy-Weinberg Equilibrium

Answer 10

p = dominant allele
p^2 = frequency of the genotype AA (dominant homozygous)
q = recessive allele a
q^2 = frequency of aa (recessive homozygous)
2pq = frequency of Aa (heterozygous)

Question 11

Practice Question: 1 in 2500 Australian Caucasian newborns have cystic fibrosis.
C for normal is dominant over c for cystic fibrosis.
Calculate the number of carriers (Cc) in the population

Answer 11

Recessive cc=q^2=1/2500
q = 1/50=0.02 = 0.02 of the population have a c allele
q^2 = 0.0004 of the population have cc (cystic fibrosis)

Dominant CC = p^2
p+q=1
p=1-0.02=0.98
p = 0.98 of the population have a C allele
p^2= 0.9604 of the population have CC

Carriers Cc = 2pq
2pq = 2(0.02)(0.98) = 0.0392
2pq = 0.0392 of the population are carriers (Cc)

Therefore 0.98 + 2(0.98)(0.02) + 0.0004 = 1

Question 12

What are the assumptions of the Hardy-Weinberg Equilibrium?

Answer 12

The population is large
Mating is random
Individuals of all genotypes must be able to reproduce (no genotype selection)
No random mutations (Dominant (A) becomes recessive (a) spontaneously)
Must be a dominant or recessive trait –> Mendelian inheritance must be maintained
No significant immigration of individuals with allele frequencies different from the endogenous population

Question 13

What does a deviation in the Hardy-Weinberg equilibrium show?

Answer 13

That the population has undergone one or more of Selection, Migration, Mutation or Non-Random Mating. Give us an indication of the reason for a genetic evolution (change) within a given population

Question 14

What are the two types of selection?

Answer 14

Negative and Positive (Selective Advantage) Selection

Question 15

Give an example of a disease that is negatively selected and describe it

Answer 15

Duchenne’s Muscular Dystrophy (DMD)
X-Linked recessive disease
Mutation in dystrophin gene –> structural component of muscle cells

Question 16

Why does the observed incidence of a disease remain the same in a population despite being negatively selected.

Answer 16

Due to the development of new spontaneous mutations.

Question 17

Give an example of a disease with a selective advantage and describe it

Answer 17

Sickle Cell Anaemia
Autosomal Recessive (amino acid substitution in the beta glob in gene –> misfiling of haemoglobin –> deformation of RBCs)
Protects against malaria as the pathogen can’t consume the haemoglobin like it normally would.
Both SS and ss are subjected to selection by malaria and anaemia.
Ss have the greatest reproductive fitness

Question 18

What is the Founder Effect and discuss and example

Answer 18

The loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population.
Example:
Colour blindness in Micronesia (Prevalence=10%, rest of world 1:33000)
Typhoon devastated the population, only 20 survived.
One was a carrier for achromatopsia.
Due to the reduced population size, this allele became more prevalent in the remaining population.