7B Populations and Evolution Flashcards
Define allele frequency
how often an allele appears in a population
define evolution
the process by which organisms become more adapted to their environment over time
define speciation
the formation new species
define variation
the measure by which organisms differ
name the sources of variation
- most commonly due to mutations
changes in the genotype often lead to changes in the phenotype
these can be advantageous or disadvantageous and might be inherited - meiosis
random mixing of chromosomes - random fertilisation
What is differential reproductive success?
The difference between an organism in which a variation was a benefit and an organism in which the same variation was a disadvantage
Describe natural selection
alleles offering an advantage are more likely to be inherited, this leads to an increase in the allele frequency
this process that leads to the change in frequency is natural selection
describe selection pressure
Changes due to variation can fore an entire population to adopt the new phenotype or for extreme phenotypes to be lost
What are the three types of selection?
directional, stabilising, disruptive
Describe directional selection
an extreme phenotype is favoured and the mean shifts to one side, usually as a result of environmental changes
Describe stabilising selection
Where extreme phenotypes reduce in frequency and the mean is favoured, due to a stable environment
Describe disruptive selection
Both extremes of a phenotype are favoured and the ‘mean’ reduces in frequency, results in almost two separate population
Define gene pool
term used to describe the collection of all genes present in all species of a population
Describe the process of speciation
when there is a large change in the allele frequency, this could lead to the creation of a new species
Two individuals must become reproductively isolated and have very different one pools to become different species
What are the two types of speciation?
Allopatric and sympatric
Describe allopatric speciation
Geographic isolation, leading to different environments, eg natural event like earthquake or volcano, or a new species landing on island
no genetic drift between individuals, variation increases as species adapt
Describe sympatric speciation
doesn’t require geographic isolation, instead one species gains a mutation that gives them an advantage and allows them toil a new niche
the ancestral population do not benefit from the new niche and continue without the mutation allowing both populations to drift apart
Describe artificial selection
evolution isn’t always a natural process,
humans often force breeding between organisms to produce beneficial breeds, this is selective breeding
Describe genetic drift
only happens in small population,
the gains or losses of alleles in individuals causes a significant allele frequency change of the population
a genetic drift from the norm
