Estimating Risk of Inherited Genetic Disease

Question 1

Define fitness

Answer 1

The relative ability of organisms to survive and pass on genes

Question 2

How can alleles affect fitness

Answer 2

In most cases not at all (natural allele)
Sometimes decrease (deleterious allele)
Rarely increase (advantageous allele)

Question 3

What is population genetics

Answer 3

The frequency of alleles in the whole population affects the health of the population

Question 4

How many alleles does a gene have

Answer 4

2

Question 5

If 800 people have the genotype AA, 190 Aa and 10 aa out of the population of 1000. Calculate the genotype frequency of each

Answer 5

AA - 800/1000 = 0.8
Aa - 190/1000 = 0.19
aa - 10/1000 = 0.01

Question 6

Calculate the allele frequency of 800 people with the genotype AA, 190 Aa and 10 aa out of the population of 1000

Answer 6

Alleles: 1600 A + (190 A + 190 a) + 20 a = 2000
Frequency of A (p) = (1600 + 190)/2000 = 0.9
frequency of a (q) = (190 + 20)/2000 = 0.1
p+q = 1.0

Question 7

Overall how can genotype frequencies be calculated

Answer 7

AA:Aa:aa = p^2:2pq:q^2

Question 8

Overall how can allele frequencies be calculated

Answer 8

A:a
= 2p^2+2pq:2pq+2q^2
= p(p+q) : q(p+q)
= p:q

Question 9

What happens to allele frequencies from generation to generation

Answer 9

Remain constant

Question 10

What happens to the relative proportion of genotype frequencies from generation to generation

Answer 10

Remain constant

Question 11

How was the consistency of allele and genotype frequencies determined

Answer 11

Hardy-Weinberg equilibrium (HWE)

Question 12

What would be required for the Hardy-Weinberg equilibrium (HWE) to occur

Answer 12

There must be an ideal population where:
Mutation can be ignored
Migration is negligible (no gene flow)
Mating is random
There is no selective pressure
Population size is large
Allele frequencies are equal in the sexes

Question 13

What increases the proportion of new alleles

Answer 13

Mutations

Question 14

How can new alleles be introduced

Answer 14

As a result of migration

Intermarriage which leads to a new gene frequency in a hybrid population

Question 15

What does non-random mating lead to

Answer 15

An increase in mutant alleles therefore increasing the proportion of affected homozygotes

Question 16

What is assortative mating

Answer 16

Choosing partners due to shared characteristics

Question 17

What is consangunity

Answer 17

Marriage between close blood relatives

Question 18

What is natural selection

Answer 18

A gradual process where biological traits become either increase or decrease in a population

Question 19

What will negative selection do

Answer 19

Reduce reproductive fitness
Decrease the prevalence of traits
Leads to the gradual reduction of mutant alleles

Question 20

What will positive selection do

Answer 20

Increase reproductive fitness
Increase the prevalence of adaptive traits
Provide heterozygote advantage

Question 21

Who does sickle cell anaemia mainly affect and what does it provide resistance to

Answer 21

Tropical Africa

Malaria

Question 22

Who does thalassaemia mainly affect and what does it provide resistance to

Answer 22

SE Asia/Mediterranean

Malaria

Question 23

Who does glucose-6-phosphate dehydrogenase deficiency (G6PD) mainly affect and what does it provide resistance to

Answer 23

Mediterranean

Malaria

Question 24

Who does cystic fibrosis mainly affect and what does it provide resistance to

Answer 24

Western Europe

Cholera/Typhoid

Question 25

Who does congenital adrenal hyperplasisa (CAH) mainly affect and what does it provide resistance to

Answer 25

Yupik Eskimos

Influenza B

Question 26

Who does GM2 gangliosidosis (Tay-sachs) mainly affect and what does it provide resistance to

Answer 26

E. European Jews

TB

Question 27

What is the benefit of a large population

Answer 27

It can balance out fluctuations

Question 28

What can a small population size exhibit

Answer 28

Genetic drift

Founder effect

Question 29

What is genetic drift

Answer 29

A random fluctuation of one allele transmitted to a high proportion of offspring by chance

Question 30

What is the founder effect

Answer 30

The reduction in genetic variation which results when a small subset of a large population is used to establish a new colony

Question 31

How can genetic drift occur

Answer 31

There is a statistical drift of gene frequencies due to chance or random events rather than natural selection in the formation of successive generations

Question 32

How can the founder effect occur

Answer 32

Genetic drift will occur in the original population to produce a bottleneck effect that reduces genetic diversity
As repopulation begins to occur, a new colony will be started by a few members of the original population (founder effect) to produce limited genetic variation

Question 33

When is the HWE useful

Answer 33

When calculating risk in genetic counselling

For planning population based carrier screening programmes

Question 34

What is fitness

Answer 34

The relative ability of organisms to survive (long enough) to pass on their genes

Question 35

What type of alleles are there

Answer 35

Natural
Deleterious
Advantagous

Question 36

Which alleles can affect fitness

Answer 36

Deleterious - Sometimes decrease

Advantageous - Rarely increase

Question 37

What can change the importance of different alleles

Answer 37

Selective pressures

This is known as population genetics

Question 38

How can mutations in dominant and X-linked conditions occur

Answer 38

Inheritance

De novo

Question 39

What is a de novo mutation

Answer 39

An alteration in a gene that is present for the first time in one family member as a result of a mutation in a germ cell (egg or sperm) of one of the parents or in the fertilized egg itself