Natural Selection Flashcards
Natural selection
process in which certain inherited traits increase the rate of survival and reproduction; tends to reduce both phenotypic and genetic variation in populations in various ways; differential survival and reproduction of individuals due to differences in phenotype
Selection for
a trait causes both it and its underlying allele(s) to increase in frequency
Selection against
a trait causes both it and its allele(s) to decrease in frequency
Adaptation
match between organisms and their environment: natural selection is the main cause of adaptation
Fitness
quantitative measure of how much an individual w/ a particular phenotype or genotype will contribute to the next generation
Which phenotype will have more offspring, the one w/ low fitness or the one w/ high fitness?
High fitness
In evolutionary biology, an organism’s fitness is measured by its
stability in the face of environmental change
genetic variability
contribution to the gene pool of the next generation
mutation rate
contribution to the gene pool of the next generation
Direction selection
an increase in the frequency of a trait or allele due to a fitness benefit; causes the trait distribution or allele frequency to change directionally (move to the right or left); common when environments change
In the finches case, how did the natural selection happen?
Selection against smaller beaks
Selection favoring smaller beaks
Selection favoring drought tolerant finches
Selection against bigger finches
Selection against smaller beaks
Why did the finches w/ large beaks survive more than the finches w/ small beaks? (I.e., large beaked finches had higher fitness)
Because large individuals always have higher fitness
Because large birds are drought tolerant
Because there were mostly large seeds to feed on
Because there were mostly large seeds to feed on
What is an example of directional selection for a certain allele affecting genotype?
No natural selection
AA: 1.0
Aa: 1.0
aa: 1.0
Directional selection for the A allele
AA: 1.0
Aa: 0.95
aa: 0.9
Disruptive selection
selection for the extremes of the trait distribution; also can be thought of as selection against the mean trait value; causes bimodal trait distribution
Ex: Timema stick insects have two forms, each adapted to be camouflaged on a diff. plant. Intermediate forms are poorly camouflaged on both plants, selecting against them.
Stabilizing selection
selection to remain at or around a mean trait value; selection against deviations from average or optimal type; can counteract fluctuations in traits caused by mutation, gene flow, or drift; more narrow distribution
Ex: infant mortality rapidly increased for babies that were much lighter or heavier than the average
Since 1951, modern medicine has decreased infant mortality due to birth weight. Compared to the data from 1951, how would we expect the distribution of infant birth weights to change?
The distribution should become wider
No change in the distribution
The distribution should become more narrow
The distribution should increase directionally
The distribution should become wider
Sexual selection
natural selection for the ability to acquire mates; major driver of sexual dimorphism; Ex: competition among males to impress females and mate
