Evolution Flashcards
(13 cards)
Factors affecting evolution
1) mutations- different alleles forms new alleles leads to genetic variation
2) gene flow- movement of alleles between populations for eg, immigration and migration
3) genetic drift- occurs in small populations, appearance of a new allele has a greater impact
4) natural selection- increase of individuals with advantageous allele
Impact of small populations
1) smaller gene pool
2) less alleles therefore less variation
3) selection pressures can affect small populations as they cannot adapt as well and are more likely to become extinct.
4) density dependent factors- affect populations depending on the size for eg, predation and competition, disease
Density independent factors- affect populations of all size for example, climate change and nature disasters
What is the genetic bottle neck
1) a large reduction in population size.
2) the gene pool along with genetic diversity, is greatly reduced
3) a selective pressure could occur and could wipe out complete gene pool, remaining individuals is not a representation of the og pop
What is the founders effect
1) small pops can arise due to new colonies by a few isolated individuals
2) these small pops have smaller gene pools and display less variation
3) frequency of rare alleles much higher and will have a much bigger impact during natural selection
4) foe eg the Amish people only marry within and have a closed community.
What is stabilising selection
- occurs in general
- most common and average phenotype is selected
- extremes are selected against
- for example baby weight
What is directional selection
- occurs during a selection pressure
- only one extreme is selected during to an advantageous allele
- average phenotype selected against
- evolution occurs as they would survive
- for example the peppered moths
What is disruptive selection
- occurs during selection
- both extreme phenotypes are selected and the average phenotype is selected against
- for example bright bird feathers against dull feathers
What is allopatric speciation
- when some members are separated from rest of group by physical barrier ( river )
- they are geographically isolated
- different environments have different pressures, therefore the species would have different adaptations
- two new species are formed as they cannot breed
What is sympatric speciation
- occurs within populations that share the same habitat
- can occur when different species breed and produce fertile offspring
- forms a new species, cannot breed with parent species which stops gene flow and reproductively isolates these hybrids
Problems caused by inbreeding
- limits the gene pool , decreasing genetic diversity reducing chance of inbred organisms evolving
- genetic disorders because can inherit both recessive and become homozygous
Assumptions on hardy winburg
- no mutations- alleles do not change or become new
-no gene flow- no migration of individuals so new new alleles introduced
- infinite pop size- pop size large enough to avoid affect of genetic drift
- no natural selection- all genotypes have equal chance of survival
Define epistasis
Interactions of genes at different loci where one gene inhibits expression of another
Define autosomal linkage
Genes that are linked are found on one of the other pairs of chromosomes
