Estimating Risk of Inherited Genetic Disease

Question 1

Define Fitness

Answer 1

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

Question 2

If an allele reduces reproductive fitness, what is this known as ?

Answer 2

Deleterious allele

Question 3

If an allele increases reproductive fitness, what is this known as ?

Answer 3

Advantageous allele.

Question 4

If an allele doesn’t impact reproductive fitness, what is this known as ?

Answer 4

Neutral allele

Question 5

Name two diseases that are recessive.

Answer 5

Sickle cell disease
Thalassaemia

Question 6

Where are de novo mutations common?

Answer 6

In dominant disorders especially where disease reduces reproductive fitness

Question 7

What kind of mutation is responsible for learning difficulty syndromes?

Answer 7

De novo

Question 8

People : 800 AA + 190 Aa + 10 aa = 1000 total

Work out the genotype frequency for the following-
AA
Aa
aa

Answer 8

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

Question 9

People : 800 AA + 190 Aa + 10 aa = 1000 total
Alleles : 1600 A + (190 A + 190 a) + 20 a = 2000

Work out the allele frequency for the following-
A(p)

Answer 9

1600 + 190 = 0.9
————–
2000

Question 10

People : 800 AA + 190 Aa + 10 aa = 1000 total
Alleles : 1600 A + (190 A + 190 a) + 20 a = 2000

Work out the allele frequency for the following-
A(q)

Answer 10

2000

Question 11

p=q=>?

Answer 11

1

Question 12

State the equation for the Hardy Weinburg.

Answer 12

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

^=squared

Question 13

P^2=?

Answer 13

p^2 = dominant homozygous frequency (AA)

Question 14

2pq = ?

Answer 14

2pq = heterozygous frequency (Aa)

Question 15

q^2 =?

Answer 15

q^2 = recessive homozygous frequency (aa)

Question 16

Discuss the frequency of allele frequencies

Answer 16

Allele frequencies remain constant generation to generation.

Question 17

Discuss the relative proportion of genotype frequencies

Answer 17

Relative proportion of genotype frequencies remain constant generation to generation.

Question 18

What are some of the assumptions made when using the HW equation?

Answer 18

• Mutation can be ignored
• Migration is negligible (No gene flow)
• Mating is random
• No selective pressure
• Population size is large
• Allele frequencies are equal in the sexes

Question 19

What increases the proportion of new alleles?

Answer 19

Mutation

Question 20

What does the introduction of new alleles through migration/intermarriage lead to?

Answer 20

New gene frequency in hybrid population.

Question 21

What does non-random mating lead to?

Answer 21

An increase mutant alleles, thereby increasing proportion of affected homozygotes

Question 22

Define Assortative mating

Answer 22

Choosing of partners due to shared characteristics
Deafness & sign language

Question 23

Define Consanguinity

Answer 23

• Marriage between close blood relatives.

Question 24

Name two founder effects

->(the reduction in genomic variability that occurs when a small group of individuals becomes separated from a larger population)

Answer 24

Physical or cultural isolation

Question 25

Describe natural selection.

Answer 25

A gradual process by which biological traits become either more or less common in a population.

Question 26

Discuss Negative selection

Answer 26

• Reduces reproductive fitness.
• decreases the prevalence of traits.
• leads to gradual reduction of mutant allele.

Question 27

Discuss positive selection

Answer 27

• Increases reproductive fitness.
• Increases the prevalence of adaptive traits.
• Heterozygote advantage.

Question 28

What three recessive conditions mean that you are resistant to malaria?

Answer 28

Thalassaemia
Sickle cell anaemia
Glucose-6-phosphate dehydrogenase deficiency (G6PD)

Question 29

If you have cystic fibrosis, what will you be resistant to?

Answer 29

Cholera/Typhoid

Question 30

If you have Congenital Adrenal Hyperplasia (CAH) what will you be resistant to?

Answer 30

Influenza B

Question 31

If you have GM2 gangliosidosis (aka Tay-Sachs) what will you be resistant to?

Answer 31

TB

Question 32

What can smaller populations have?

Answer 32

Genetic Drift
Founder effect

Question 33

Define genetic drift.

Answer 33

Random fluctuation of one allele transmitted to high proportion of offspring by chance.

Question 34

Define founder effect

Answer 34

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

Question 35

Discuss genetic drift.

Answer 35

Mutations (alleles) are widespread and neutral.

Statistical drift of gene frequencies due to chance or random events rather than natural selection in the formation of successive generations

Question 36

What does the bottleneck effect do?

Answer 36

Reduces genetic diversity

Question 37

What is the HW equation useful for?

Answer 37

Useful for calculating risk in genetic counselling

Useful for planning population based carrier screening programmes