20.5 Evolution Flashcards
Define GENE POOL
The sum total of all the alleles present in the population at a time
Define ALLELE FREQUENCY
The relative frequency of an allele in a population at a given time
What is the HARDY-WEINBERG PRINCIPLE:
That in a stable population with no disrupting factors the allele frequencies will remain constant from one generation to the next and there will be no evolution
Conditions for the HARDY-WEINBERG PRINCIPLE to be in effect:
- large and isolated population
- random mating
- no mutations
- no selection pressures
Factors affecting Evolution
- mutation
- sexual selections
- gene flow
- genetic drift
- natural selection
Define SEXUAL SELECTION
natural selection as a result of the characteristics an individual possesses which is favoured by the opposite sex
(what makes an individual attractive)
Define GENE FLOW
the transfer of alleles from one population to another
Define GENETIC DRIFT
the random changes of allele frequencies in a population
What is a SELECTION PRESSURE? Give examples
a factor in the environment which causes individuals to compete against one another or a factor that causes fitness or behavioural changes in an individual
Examples: illness, scarcity of food and water, shelter
What is a GENETIC BOTTLENECK?
this is a large reduction in genetic variation and a reduced gene pool. they occur as a result of a catastrophic event in which mass amount of the population dies.
however they allow for higher allele frequencies of beneficial alleles to be spread quicker
What is the FOUNDER EFFECT?
an extreme form of genetic drift, this is when a small group of individuals colonise a new area, their offspring initially experience low genetic variation due to the small colonising group having a small gene pool.
however, rare alleles have the potential to become more common in the population due to the conditions of the new environment
What is STABILISING SELECTION?
a form of natural selection that favours average phenotypes, it is disadvantageous to be an extremity ie, too tall or too small.
this form of selection causes a random distribution curve to stand taller with a smaller base
What is DIRECTION SELECTION?
a form of natural selection that favours one extreme phenotype over the other extreme and norm phenotypes.
ie, peppered moths, advantageous to be black in urban areas than white, for camouflage, so more black moths
this form of selection causes a random distribution curve to move to the left or right
What is DISRUPTIVE SELECTION?
a form of natural selection where both the extremities are favoured and not the norm, usually a result of the same species inhabiting differing habitats and leads to new species
ie, Darwin’s finches
this form of selection causes a random distribution curve to take on a camel back like shape
