Theme 4B Flashcards
What are the 2 formulas to calculate allele and genotype frequencies for a population
p + q = 1 and p^2 + 2pq + q^2 = 1
Why is HWE a good null hypothesis for evolutionary change
There is no change in allele frequencies
How can you determine whether a species is in HWE
1) calculate allele frequencies
2) use allele frequencies to calculate expected genotype frequencies p^2, 2pq, q^2
3) calculate expected numbers HWE
4) compare observed to expected values (chi-square test)
How do you predict genotype frequencies for populations assumed to be in HWE
Uses hardy weinberg equation
(# recessive phenotype)/(total #) = q^2
q = (square root)q^2
p = 1 - q
What are the 5 major assumptions of HWE
1) no mutation
2) no migration (gene flow)
3) population is infinitely large
4) no natural selection
5) mating is random
Is the frequency of an allele the same in a population as the ratio in a single cross
NO
What are Darwin’s 4 constrictions for evolution by natural selection
1) individuals within a species vary
2) some variations passed to offspring (heritable)
3) more offspring are produced that can survive/reproduce
4) survival and reproduction is not random, but related to phenotypic variation
What does HWE tell us
When evolution is not occurring
Can predict genotype frequencies when we have less information about a population
NOTE: even if a population is not in HWE this does not mean it is evolving, have to see a sustained change in allele frequencies
How can you determine the allele frequency in a sample of n individuals
The number of occurrences of the allele divided by twice the number of individuals in the sample (2n)
How do you determine the degree of freedoms used
genotypes - # alleles
What is quantitative variation
Individuals differ in small, incremental ways (displayed on a bar graph or curve)
Characteristics exist in 2+ discrete states and intermediate forms are absent
What is polymorphism
Existence of discrete variants of a character
Traits are described as polymorphic
What are single nucleotide polymorphisms (SNP’s)
Polymorphisms that can exist between individuals and that have shown to account for about 90% of genetic variation in humans
How many new combinations are alleles are there in humans
More then 10^600
But there are less then 10^10 alive today so it is unlikely anyone with your genotype has lived or ever will (unless you have an identical twin)
