Inheritance of Sex-Linked Genes

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Ch 23
Population Genetics Its importance Its
predictive value
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Population? Define
- Group of interbreeding organisms (a species) -
Reside within a specified geographic region
Example Humans in the Pacific northwest Grey
whales in Puget Sound
Genetically related Gene pool all the alleles
within the population
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Gene frequency in a population
p frequency of dominant allele or f(dominant
allele)
q frequency of recessive allele or f(recessive
allele)
1 p q
If p0.3, then q1-0.30.7
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The frequency of every possible combination of a
given pair of alleles in a population can be
determined mathematically with
1(pq)(pq)
Expand
1p2 2pq q2
F(homozygous recessives)
F(homozygous dominants)
F(heterozygotes)
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If the frequency of cystic fibrosis, a recessive
allele, is 0.4 in Europe, 1. what is the
frequency of the normal allele?
Want to solve for p p1-0.4 0.6
2. What is the frequency of people with the
disease?
Want to solve for q2
q20.420.16
3.What is the frequency of carriers?
Want to solve for 2pq
2pq2(0.4)(0.6)0.48
4.If the population size is 20,000, how many
people have the disease?
q2(20,000)3,200
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Genotype of population--gtphenotype
Some phenotypes adaptive (advantageous)--gt in
creased fitness (fertility)
Someneutral --gt fitness unchanged
Others negative --gt decrease fitness
Consider frogs adaptive traits neutral negativ
e
Ability to leap away from predators
Color of toenails
Inability to live in arid environment
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Genetic change--gt phenotypic change--gtimpacts
fitness
Evolutionary ecologists take all these factors
into account.
Focus on
Changes in a populations gene pool --gt changes
in gene frequency in a population
Microevolution
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1 p q
Hardy-Weinberg equilibrium
1p2 2pq q2
Assumes no change over time no evolution from
one generation to the next
Equilibrium Conditions
1. No DNA mutation
2. No natural selection
3. No migration (no gene flow between
populations)
4. Random mating
5. Large population
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Hardy and Weinberg must be joking!
A static environment no change!
I would question that.
When changes in allele frequencies occur, how
does one determine the cause? What significance
does it have if any?