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Flashcards in Lecure 35 Deck (14):

Give examples where heterozygote is the fittest?

-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


How does fitness change allele frequencies?

-can a lot


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

-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


What are the three types of selection?



What is stabilizing selection?

-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


What is disruptive selection?

-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


What is directional selection?

-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)


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

-stable or balanced polymorphism polymorphism


How does selection affect allele frequencies?

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


What are two types of non random mating?

-- 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


What does consanguinity and self fertilisation do?

-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.....


What is citrullineamia?

-caused by the fact that one bull carrying it had loads of offspring
-• Autosomal recessive • Mutation in gene which affects production arginosuccinate
• 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


How does mutation influence allele frequencies?

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


How is migration calculated? and allele frequencies

-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