DLA 10a Population And evolutionary genetics part A

Question 1

Analyze a biallelic system

Answer 1

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

Question 2

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

Answer 2

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

Question 3

What is the Hardy Weinberg equilibrium equation?

Answer 3

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

Question 4

What does hardy Weinberg equation describe?

Answer 4

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

Question 5

Genotypes are _______ created

Answer 5

Randomly

Question 6

Why are genotypes randomly created?

Answer 6

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

Question 7

What does the Hardy Weinberg equation allow us to do?

Answer 7

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)

Question 8

The higher the frequency of a dominant allele …

Answer 8

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

Question 9

How is the frequency affected across generations?

Answer 9

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

Question 10

What is the simplifying rule?

Answer 10

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

Question 11

Why are deleterious alleles never eliminated?

Answer 11

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

Question 12

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

Answer 12

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