DLA 10a Population And evolutionary genetics part A Flashcards

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1
Q

Analyze a biallelic system

A

A-dominant allele (or more common allele)= p

a-recessive allele(or the less common allele)= q

We recognize that there can be 3 possible genotypes:

  1. AA
  2. Aa
  3. aa
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2
Q

What are the requirements under which binomial expansion may be applied to genetics for populations?

A

If alleles are randomly distributed in a large population

And there are no factors selecting for or against any particular genotype

This relationship will follow the mathematics of the binomial expansion

-(p+q)^2

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3
Q

What is the Hardy Weinberg equilibrium equation?

A

(P+q)^2= p2 +2pq+q2

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4
Q

What does hardy Weinberg equation describe?

A

This equation describes the distribution of genotypes in people

So “1”=the whole population, and each component of p2+2pq+q2 represents the fraction of the population

p^2= fraction of people who have genotype for dominant alleles

q^2= fraction of people who have genotype of recessive allele

2pq= fraction of carriers

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5
Q

Genotypes are _______ created

A

Randomly

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6
Q

Why are genotypes randomly created?

A

Randomness comes from meiosis, and independent assortment

So when 2 different populations (same species) meet and randomly mate, only 1 generation is needed to achieve a new Hardy Weinberg equilibrium for all alleles, at all loci

-randomness ensures that the mathematically described distributed will be followed

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7
Q

What does the Hardy Weinberg equation allow us to do?

A

Allows us to relate allele frequency to genotype frequency

Allele frequency (for a given locus):

  • number of alleles in the population that are dominant(A)
  • number of alleles in the population that are recessive(a)
  • Can be obtained by counting the alleles directly, or back calculating from phenotype(as will be explained later)
  • Alleles are found within people (if autosomes, each person has alleles)
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8
Q

The higher the frequency of a dominant allele …

A

As p/frequency of the dominant allele increases and q2 becomes more and more rare, the vast majority of recessive alleles are marked as carriers, and less are marked as homozygous

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9
Q

How is the frequency affected across generations?

A

The frequency of a is halved in two generations and halved again by the sixth generation

Subsequent reductions occur slowly because the majority of a alleles are carried by heterozygotes

We can’t eliminate all q*2 possibilities as 2pq allows it to be possible

Spontaneous mutation in gametogenesis allows for a steady state rate at low frequencies

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10
Q

What is the simplifying rule?

A

If q is small, then estimate that p is qapproximately = 1

This is because incidence values/q2 from real life are only rough estimates

General rule: if q is less than 5% of all alleles, p is close enough to 1 for our calculations

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11
Q

Why are deleterious alleles never eliminated?

A

There will always be heterozygous which allows the deleterious recessive allele to exist

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12
Q

In the absence of other evolutionary forces, genotype frequencies are…

A

Expected to remain constant and the population is said to be at hardy Weinberg equilibrium

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