Natural Selection II Flashcards
Lesson 10
Explain the Tay Sachs disease and W.
the frequencies doesn’t equal 1 because the recessive allele is fatal before reproduction
What is the mean fitness?
w = p^2W(AA) + 2pqW(Aa) + q^2W(aa)
How to find the genotype frequencies in the next generation?
Divide the allele by the mean relative frequency
Ex) AA: p^2W(AA) / (w)
New allele frequencies
p= d + (h/2)
q= r + (h/2)
What are the effects of natural selection with respect to HWE?
- selection can cause allele frequencies to change from generation to generation
- Selection can cause deviation from H-W genotype
- Selection is deterministic (predictable)
- Selection can be a strong evolutionary force (compared to mutation)
What was Darwin’s Postulates about evolution by natural selection?
- individuals vary
- at least some variation is heritable
- Some individuals leave more progeny than others
- The variation in survival and reproduction is not random, but depends on heritable trait variation
What is the outcome from Darwin’s postulates?
Genetic variants with higher survival and/or reproduction increase in frequency in population
What accounts for most of the variation in natural population?
Combined action of mutation and genetic drift, as well as selection
What does diploidy do?
Maintains genetic variation in the form of recessive alleles hidden from selection in heterozygotes
What is balancing selection?
Occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population, leading to balanced polymorphism
What does balancing selection include?
*heterozygote advantage
*frequency-dependent selection
What is heterozygote advantage?
Individuals who are heterozygous at a particular locus have greater fitness than homozygotes
What is an example of balancing selection through heterozygote advantage?
People having the heterozygote allele for sickle cell disease
* have protection against malaria and have normal-ish red blood cells
What happens in frequency-dependent selection?
The fitness of any morph declines if it becomes too common in the population
Explain the scale-eating fish situation
Scale eating fish has mouths curved to either the left or right. When there is an abundance of left-mouthed fish, the prey realizes this and starts to lack attention on the left side, making right-mouth fish survive and reproduce.
This keeps flopping back and forth, as the prey and the fishes reproduce.
