Modes Of Natural Selection

Question 1

Micro evolution by natural selection =

Answer 1

Directional selection

Question 2

Directional selection

Answer 2

A change in allele frequency in one direction

• most extreme phenotype is most fit. One allele becomes more common until it reaches fixation
• tends to eliminate genetic variation over time. New mutations must replace lost

Question 3

Stabilizing selection

Optimality

Answer 3

An intermediate phenotype is favored over the extreme phenotypes

• intermediate phenotypes close to the mean are most fit. When applied to a single locus. Heterozygous most fit.= balancing selection
• decreases variation for the trait= genetic variation
• balancing for single locus: genetic variation is preserved since both alleles will be maintained

Optimality: most species are likely near their adaptions =working assumption

Question 4

Disruptive selection

Answer 4

Extreme phenotypes are favored over intermediate

Question 5

Environment affects fitness of alleles…

Take homes on selection:

Answer 5

Alleles may have different fitnesses in diff environments. Allele favored in one may have disadvantage in another

• environment change may reverse effects of selection
• doesn’t act for good of species or planet
• selection is weak against rare recessive alleles

Question 6

Best index of a individuals fitness…

Other contributors…

These are all called components of fitness

Answer 6

Lifetime reproductive success

It’s chance of living to a certain age (age specific survivorship) number of offspring during a certain time interval (age specific fecundity)

Question 7

Absolute fitness

Relative fitness

Answer 7

Per capita growth rate

Compares absolute fitness or some component of fitness of a trait relative to others