hardy weinberg and fittness Flashcards
hardy winbergy equation
p2+ 2pq + q2 =1
p+ q=
1
p=
frequency of one allele in the pop. ( dominant)
q=
frequency of other alleles (recessive)
p2=
proportion of population that is homozygous for the first alleles (RR)
2pq
proportion of the population that is heterozygous ( Rr)
q2
proportion of the population txt is homozygous for the second allele (rr)
H-W equilibrium only applies when
1) discrete generations
2) allele frequency is the same in each sex
3) mendelian segregation occurs
4) population size is large so no genetic drift
5) no gene flow (imm/em)
6) no mutation
7) mating occurs at random
8) no selection
in the case of dominant and recessive alleles
you can easily count the number of individuals with the recessive phenotype
- this will give ou the frequency of the double recessive genotype - q2 or dominant (p2.
- with that value you can go on and calc. the frequencies of all other genotypes and alleles
large population so no genetic drift
- genetic drift affects small populations
- genetic drift reduced genetic variation
no migration or gene flow
migration transfers individuals amongst population
- gene flow transfers alleles amongst population
- can either increase or decrease genetic variation
no mutation
- increase genetic variation
- some mutations create dominant alleles, some create recessive or co-dominant alleles
- mutations may be be harmful, neutral or favourable
- effect depends on environment
mating occurs at random
- non random mating does not change allele frequencies, but rather hcnages how the alleles are distributed into diploid genotypes
- commone maple of non random mating includes assertive and dissortative mating and inbreeding
assortative mating
when individuals mate with those that are similar to themselves - non random
–> leads to an increase in homozygotes
disassortative mating
breeding between individuals with dissimilar genotypes- more rare
–> increase in heterozygotes
H-W is
of limited use due to fe organisms fulfilling all of these rules
Hardy weingberg provides a way of testing whether
a population has evolved or not
-if assumptions are not met the population will evolve
if the assumptions are not met a population….
will evolve
fitness is used to
measure reproductive success
components of fitness
- survivorship
2. fecundity
where is fineness manifested within
phenotype
what is phenotype affected by
genes and environment
why may fitness of different individuals with the same genotype be different in diff environments
the fitness of a given phenotype can be diff in diff environments
e.g. polar bears white coat acts as camouflage in the north pole and would provide fitness. However if a polar bear was in the jungle its white coat would decrease its fitness
(W)
fitness
definition of fitness
W is defined as the reproductive success of a genotype relative to the optimum genotype
Fitness =
W=1-s
s
selection
what will be affected if certain alleles affect fitness
the frequency of the alleles will change over time
- alleles with higher fitness become more common–> natural selection
alleles with higher fitness will
become more common –> NS
methods of measuring fitness
- measure relative survival of the genotypes within a generation. Kettle well;s mark-recapture experiment with he peppered moth is an example.
- measure changes in gene frequencies between generation; we then substitute the measurements in the formula that expresses fitness in terms of gene frequencies in successive generations
- measure deviation from H-W ratios- this is used in estimating fitness in the case off sickle cell anaemia
what is measuring deviation from H-W ration used in
measuring fitness in the case of sickle cell anaemia
