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
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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
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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
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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
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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
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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
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Natural selection
Gradual process where traits become more or less common in a population
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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
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Give some examples of heterozygote advantage
Cholera/ typhoid with CF
Sickle cell anaemia for malaria
G6PD for malaria
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What do large populations do to fluctuations?
Balance them out
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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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