9.4- TYPES OF SELECTION Flashcards
What is selection?
process by which organisms that are better adapted to their environment tend to survive + breed, while those that are less well adapted tend not to
What is directional selection?
selection may favour individuals that vary in one direction from mean of population
What does directional selection do?
changes characteristics of population
What is stabilising selection?
selection may favour average individuals
What does stabilising selection do?
preserves characteristics of population
What are most characteristics influenced by?
more than one gene (polygenes)
What are the characteristics that are influenced more than one gene, more influenced by?
more influenced by environment than ones determined by single gene
What does the effect of the environment on polygenes produce?
individuals in population that vary about the mean
What is phenotype?
observable physical + biochemical characteristics of organism
Who are most likely to survive if the environmental conditions change? (directional selection)
phenotypes that are best suited to new conditions are most likely to survive
What will happen to the mean overtime? (directional selection)
mean will move in direction of individuals with phenotypes best suited to new conditions
Directional selection: bacterial resistance to penicillin- what was the mutation? #1
spontaneous mutation occurred in allele of gene in bacterium that enabled it to make new protein
Directional selection: bacterial resistance to penicillin- what was the new protein that the bacterium was able to make? #2
new protein was enzyme that broke down antibiotic penicillin before it was able to kill bacterium
enzyme called penicillinase
Directional selection: bacterial resistance to penicillin- what did the mutation give the bacterium? #3
advantage in being able to use penicillinase to break down antibiotic + so survive while rest of population of bacteria were killed by it
Directional selection: bacterial resistance to penicillin-what was the bacterium that survived able to do? #4
able to divide by binary fission to build up small population of penicillin-resistant bacteria
Directional selection: bacterial resistance to penicillin- what were the members of the small penicillin-resistant population more able to do? #5
more able to survive, + so multiply in presence of penicillin than members of non-resistant population
Directional selection: bacterial resistance to penicillin- what happens to the population of penicillin-resistant bacteria? #6
population of penicillin-resistant bacteria increased at expense of non-resistant population
so frequency of allele that enables production of penicillinase increased in population
Directional selection: bacterial resistance to penicillin- what happens to the population’s normal distribution curve? #7
population’s normal distribution curve shifted in direction of population having greater resistance to penicillin
Directional selection: bacterial resistance to penicillin- do the bacteria mutate because of the presence of bacteria?
NO- mutations occur randomly + very rare
What does directional selection result in?
phenotypes of one extreme of population being selected for + those at other extreme being selected against
If environmental conditions remain stable, who are favoured? (stabilising selection)
individuals with phenotypes closest to mean that are favoured
What does stabilising selection tend to eliminate?
phenotypes at extremes
What does stabilising selection result in?
phenotypes around mean of population being selected for and those at both extremes being selected against
What does natural selection result in?
species that are better adapted to environment they live in
What may be the adaptations for natural selection? (3)
anatomical
physiological
behavioural