Estimating Risk of Inherited Genetic Disease COPY COPY Flashcards

1
Q

Define fitness

A

The relative ability of organisms to survive and pass on genes

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2
Q

How can alleles affect fitness

A
In most cases not at all (natural allele)
Sometimes decrease (deleterious allele)
Rarely increase (advantageous allele)
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3
Q

What is population genetics

A

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

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4
Q

How many alleles does a gene have

A

2

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5
Q

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

A

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

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6
Q

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

A

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

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7
Q

Overall how can genotype frequencies be calculated

A

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

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8
Q

Overall how can allele frequencies be calculated

A

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

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9
Q

What happens to allele frequencies from generation to generation

A

Remain constant

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10
Q

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

A

Remain constant

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11
Q

How was the consistency of allele and genotype frequencies determined

A

Hardy-Weinberg equilibrium (HWE)

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12
Q

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

A
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
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13
Q

What increases the proportion of new alleles

A

Mutations

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14
Q

How can new alleles be introduced

A

As a result of migration

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

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15
Q

What does non-random mating lead to

A

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

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16
Q

What is assortative mating

A

Choosing partners due to shared characteristics

17
Q

What is consangunity

A

Marriage between close blood relatives

18
Q

What is natural selection

A

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

19
Q

What will negative selection do

A

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

20
Q

What will positive selection do

A

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

21
Q

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

A

Tropical Africa

Malaria

22
Q

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

A

SE Asia/Mediterranean

Malaria

23
Q

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

A

Mediterranean

Malaria

24
Q

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

A

Western Europe

Cholera/Typhoid

25
Q

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

A

Yupik Eskimos

Influenza B

26
Q

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

A

E. European Jews

TB

27
Q

What is the benefit of a large population

A

It can balance out fluctuations

28
Q

What can a small population size exhibit

A

Genetic drift

Founder effect

29
Q

What is genetic drift

A

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

30
Q

What is the founder effect

A

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

31
Q

How can genetic drift occur

A

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

32
Q

How can the founder effect occur

A

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

33
Q

When is the HWE useful

A

When calculating risk in genetic counselling

For planning population based carrier screening programmes

34
Q

What is fitness

A

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

35
Q

What type of alleles are there

A

Natural
Deleterious
Advantagous

36
Q

Which alleles can affect fitness

A

Deleterious - Sometimes decrease

Advantageous - Rarely increase

37
Q

What can change the importance of different alleles

A

Selective pressures

This is known as population genetics

38
Q

How can mutations in dominant and X-linked conditions occur

A

Inheritance

De novo

39
Q

What is a de novo mutation

A

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