Lecture 10- Population genetics Flashcards
Requirements for natural selection to occur
- variation in traits
- traits vary in how the impact survival/ reproduction
- traits are heritable
genetic variation
refers to the differences in genes or other DNA sequences among individuals
phenotype
physical features expressed by the genotype
Discrete traits
single gene determines phenotypic differences and can usually be classified on an either-or basis
Quantitative traits
two or more genes usually vary the phenotype in gradations along a continuum
Neutral variation
differences in DNA sequence that do not confer a selective advantage or disadvantage.
synonymous mutations
change in the dna sequence that codes for amino acids but does not change the encoded AA
Nonsynonymous mutation
change the protein sequences and are frequently subjected to natural selection
what prevents natural selection from reducing genetic variation to only the favorable alleles?
- Recessive alleles hidden from selection i heterozygotes
- heterozygote advantage
- selection can preserve variation
Sexual selection
individuals with certain inherited characteristics are more likely than others of the same sex to obtain mates
intrasexual
individuals of one sex compete directly for mates of the opposite sex
intersexual
individuals of one sex are choosy in selecting their mates from the other sex
sexual dimorphism
a difference in secondary sexual characteristics between males and females
frequency-dependent selection
fitness of a phenotype depends on how common it is in the population
negative frequency dependent selection
rare genotypes have a fitness advantage
positive frequency dependent selection
common genotypes have a fitness advantage
relative fitness
contribution an individual makes to the gene pool of the next generation relative to the contributions of others
relative fitness is determined by the
survival/ reproductive rate of a genotypic relative to the maximum survival/ reproductive rate of other genotypes
Most fit genotype should always have a relative fitness of
1.0
if reproductive rates are all equal (RF)
each survival rate divided by the highest survival rate
If survival rates are all equal (RF)
each reproductive rate divided by the highest reproductive rate
Selection coefficient (s)
the relative strength of selection acting against a genotype
- s= 1- w w= relative fitness
selection coefficient of 0 means
genotype is not being selected against (strong)
selection coeff of 1 means
total selection, individuals produce no viable offspring
selection coeff of 0.1 means
individuals with that genotype produce offspring at 90% of the fittest genotype
P (frequency of A) + q (frequency of a) =
1, this will always be true
Hardy-Weinberg principle
predicts what genotype frequencies and allele frequencies will occur in the next generation
the Hardy- Weinberg principle assumes evolution
is not occuring
Assumptions of Hardy- Weinberg Equilibrium
- NO selection
- No mutation
- No migration
- Large population
- random mating
Gene pool
all of the alleles from all the gametes produced in each generation
Calculate the frequency of alleles
[2(# homozygous individuals) + # of alleles from heterozygous individuals] / total # alleles
After calculating p, how do you find q?
q= 1-p
Calculate the expected frequency of
homozygous dominant
p^2
Calculate the expected homozygous recessive
q^2
Calculate the expected heterozygous frequency
2pq
How to tell if a population is in HW equilibrium?
If the expected frequencies are equal to the observed frequencies.
How to calculate the expected # of individuals for that genotype
Multiply the frequency by the total number of individuals
Can you always calculate allele frequencies from genotype frequencies?
Yes you can because the genotype predicts the phenotype
Can you always calculate genotype frequencies from allele frequencies?
sometimes, you can if the population is in HW equilibrium
