types of selection Flashcards
(13 cards)
what is selection?
the process by which organisms that are better adapted in their environment tend to survive and breed, while those that aren’t well adapted tend not to
what is directional selection in simple terms?
selection may favour individuals that vary in one direction from the mean of the population, this changes the characteristics of a population
what is stabilising selection?
selection may favour average individuals, this preserves the characteristics of a population
what are most characteristics influenced by?
more than one gene- polygenetic
the environment also has large influence on these characteristics
the combination of these two factors (polygenes and environment) produces individuals that vary about the mean
if this data is plotted, it gives a NORMAL DISTRIBUTION CURVE
when does directional selection occur?
in response to environmental change
who is more likely to survive and reproduce in directional selection?
individuals with alleles for a single extreme phenotype
what happens to the mean/mode and SD in directional selection?
mean/mode shifts in one direction
SD remains same
when does stabilising selection occur?
when the environment is not changing
who is more likely to survive and reproduce in stabilising selection?
individuals with alleles for phenotypic characteristics towards the mean are more likely to survive and pass on alleles
those with phenotypes at the extremes are less likely so stabilising selection tends to eliminate phenotypes at extremes
how are the mean/mode and SD affected by stabilising selection?
mean/mode remains same but there are an increased number of individuals with this phenotype
SD decreases
what is meant by phenotype?
observable characteristics of an organism which are the result of the genotype as well as environmental factors
what is an example of directional selection?
antibiotic resistance
what is an example of stabilising selection?
babies birth weight
