Flashcards in Estimating risk of inherited genetic disease Deck (33)
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1
Fitness
Relative ability of organisms to survive and pass on genes
2
What does fitness depend on?
Types of alleles eg neutral, deleterious or advantageous
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Do deleterious mutations sometimes or rarely decrease fitness?
Sometimes
4
Do advantageous mutations sometimes or rarely increase fitness
Rarely
5
Frequency of alleles affect healthy population
Population genetics
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1 gene with 2 alleles what are p and q
p = dominant q = recessive
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Genotype frequency
GG/total
8
Allele frequency
Gt/ total alleles ( NB double the number as alleles separate)
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Do dominant conditions become more common at the expense or recessive alleles?
NO
10
Hardy-Weinberg principle
Use quadratics
11
What are constant generation to generation?
Allele frequency and relative proportion of genotype frequency
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p squared = q squared = 2pq=
1
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What can HWE allow?
Calculate risk in genetic counselling
Plan population based carrier screening programmes
14
p squared
Homozygous dominant
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q squared
Homozygous recessive
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pq
Heterozygous
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When is HWE not always achieved?
Blood type
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Name some characteristics of an ideal population
- Mutation can be ignored and migration is negligible
- Mating is random and there are no selective pressure
- Allele frequency equal in sexes in large population
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Do mutations increase or decrease proportion of new alleles?
Increase
20
What else increases the proportion of new alleles?
Migration and intermarriage
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Give an example of migration and proportion of alleles
60% of men in NW Scotland have Scandinavian DNA and leads to a hybrid population
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What does non random mating do?
- Increase mutant alleles
- Increase affected homozygotes
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Assorative
Shared characteristic
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Consanguinity
Close blood relatives
25
Natural selection
Gradual process where traits become more or less common in a population
26
Negative natural selection
Reduces reproductive fitness
Decrease prevalence of traits
Gradual reduction of mutant allele
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Positive natural selection
Increases reproductive fitness
Increase prevalence of adaptive traits
Heterozygote advantage
28
Give some examples of heterozygote advantage
Cholera/ typhoid with CF
Sickle cell anaemia for malaria
G6PD for malaria
29
What do large populations do to fluctuations?
Balance them out
30
Genetic drift
Random fluctuation of one allele to high proportion of offspring - mutations widespread and neutral after a fire or ploughing etc
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Founder effect
Genetic drift causes this reduction in genetic variation when a small subset of large population establish new colony with limited variation eg Amish founded from a small number of German immigrants
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Bottleneck effect
Reduce genetic diversity
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