10 Flashcards
Darwin’s three postulates?
Natural selection will occur when?
•Individuals are variable in some traits
•At least some of this variation is heritable
•Individuals will reproduce better or worse depending on the trait
In 1977, what happened in daphne island?
A large drought occurred that wiped out almost all vegetation. Seeds grew large and selected for larger billed finches. About 80% of the birds died.
How to test for heritability?
Make a scatter plot with one axis being the trait of the parent and the other axis being the trait of the offspring. Look for correlations.
Lower scatter of a plot can indicate what in terms of heritability?
More heritable
Selection differential (S)?
Measuring the mean differences in a phenotype before and after selection. (Xbar_B - Xbar_P), P = original population (parents), B = population after selection
Response to selection (R)?
Differences in a phenotype from the current generation to the next generation. R = (Xbar_O - Xbar_P), P = original population, O = next generation
After the 1977 drought in daphne occurred, what happened next?
The environment became wetter and vegetation grew again. Overtime, beak size began to decrease.
Directional selection?
When selection favours phenotypes at one end of a distribution. The population evolves in that direction. It changes mean phenotype but not variance in phenotype
Stabilizing or purifying selection?
Favours values towards the middle of the distribution. The mean phenotype does not change but decreases variance in phenotype because the phenotypes at Rutgers end if the distribution have been selected against.
Disruptive selection?
Favours phenotypes towards the ends of the distribution. Mean phenotype does not change as long as individuals on both ends of the distribution have equal fitness. Variance in phenotype increases.
Frequency dependent selection?
Occurs when the fitness of a genotype depends on its frequency in the population.
Two types of frequency dependent selection?
•Negative frequency dependent selection: A phenotype has the greatest selective advantage if it is rare.
•Positive frequency dependent selection: a phenotype has the greatest selective advantage if it is common. There is strength in numbers.
Breeder’s equation? R = ?
h^2 * S, h^2 is heritability (regression).
Why could natural selection not always be beneficial for the species?
Since natural selection is favourable for the current environment but doesn’t take into account future environments. Selection also acts on individuals and not necessarily on populations.
