Lecure 35 Flashcards

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1
Q

Give examples where heterozygote is the fittest?

A
  • Protection in malarial region of
  • Thalassaemia carrier (Tt)
  • Cystic Fibrosis - Cc protects against diarrhoea (Cc)
  • PKU - protects against a fungal toxin causing miscarriage (Pp)
  • Tay-Sachs - Tt protects against Tuberculosis

-heterozygote the fittest in a number of examples= that is why the mutations are kept in the population
thalassemia= have some irregular blodd cells but offers protection against malaria
cystic fibrosis= prootects against cholera and typhoid= don’t have as many functioning Cl channels so don’t lose as much water from their bowl

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2
Q

How does fitness change allele frequencies?

A

-can a lot

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3
Q

How can H-W equilibrium restored if autosomal or X linked?

A

-When a population is not in HW equil and the trait is autosomal it can be restored in one generation of random mating NOT so for an X linked trait

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4
Q

What are the three types of selection?

A
  • stabilizing
  • disruptive
  • directional
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5
Q

What is stabilizing selection?

A
  • selection against the extremes in the phenotype

- eg. birth weight of babies= selection against the very heavy and the very light=higher risk of death

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6
Q

What is disruptive selection?

A

-selection against the intermediate phenotypes
-the opposite of stabilizing, keep the extremes and get rid of the middle
-eg:Bird beaks
birds with intermediate sized beaks are at a disadvantage
intermediate= not good at getting small or big seeds, small beak= good for small seeds and vice versa

eg.2- Batesian mimicry= bad tasting butterfly=have to be an exact match to the bad tasting ones, so the extremes have an advantage but the ones in the middle don’t if only half-way

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7
Q

What is directional selection?

A

-selection for one phenotype from the end of the phenotypic (and presumably genotypic) range Shifts the frequency of one or more phenotypes in a particular direction
-eg moths
pre industrial revolution post industrial revolution 1952 >1850s to 1952
trees with lichen trees with soot etc., light form camouflaged dark form camouflaged allele b selected for allele B selected for f(0.95)

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8
Q

What happens when selection is acting but the heterozygote is the fittest genotype?

A

-stable or balanced polymorphism polymorphism

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9
Q

How does selection affect allele frequencies?

A

-• Selection means there are differences in relative fitnesses of the genotypes
• Relative fitness changes according to the environment • Selection may change allele frequencies quickly

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10
Q

What are two types of non random mating?

A
  1. Inbreeding-consaguinity-self-fertilisation
    - - mating between related individuals (genetic relationship)
  2. Assortative mating=- select individuals like themselves (positive AM)
    - select individuals unlike themselves (negativeAM) -( not genetically related)

-Also at population level (often in plant and animal breeding ) - nonrandom mating if one individual contributes disproportionally to the next generation

-non random mating= between genetically related
=assertive mating: positive= seek out the one with similar phenotype
negative: seek one that is the opposite to you
-also when one bull chosen= sperm frozen= too much offspring-contributing disproportionally to the next generation

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11
Q

What does consanguinity and self fertilisation do?

A

-Consanguinity/inbreeding alter genotypic ratios by increasing homozygosity but doesn’t allele frequencies on its own

-However consanguinity provides the phenotypes (eg., ) on which
can act eg ., in humans CF, PKU, Thalassaemia etc.,
Human consanguinity…..

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12
Q

What is citrullineamia?

A

-caused by the fact that one bull carrying it had loads of offspring
-• Autosomal recessive • Mutation in gene which affects production arginosuccinate
synthetase
• calves die due to the inability to
• process ammonia
• 3000 deaths per year (incidence of disease in humans is 1/100,000)
• Artificial insemination generates 80% of dairy cattle
-can be detected in sperm now

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13
Q

How does mutation influence allele frequencies?

A

-• On its own minor change to allele frequencies
• Source of all new alleles
• With selection can be significant

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14
Q

How is migration calculated? and allele frequencies

A

-may be significant depending on m and difference between x and p
Looking at the formula, delta p = m(x-p) What makes migration significant?
When the difference in allele frequencies in locals (p) and migrants (x) is great.
When migration rate (m) is high.

-Therefore p = f(A) after one generation of migration = 0.4 + 0.02
f(A) =0.42

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