| What does evolution mean? (2) | cumulative change in the heritable characteristics of a population over time = encoded by genes and transferred as alleles
a change in the allele frequency of a population's gene pool over successive generations |
| How does evolution occur? | variation:
genetic mutations
chromosomal abnormalities
sexual reproduction
gene flow (migration)
selective pressures:
random events (Genetic drift)
directional forces (natural or artificial) |
| What is a mutation? | change in the nucleotide sequence in the genes
eg: germline mutations in gametes (Sex cells) can be passed to offspring |
| What are the 3 ways in which meiosis causes variation? | crossing over = DNA segments are exchanged between homologous pairs
Independent assortment = random separation of homologous pairs
Random Fertilisation = random fusion of 2 haploid gamers |
| What is gene flow? | the movement of alleles between different populations |
| How does different geographical locations cause variation within a species? (5) | they experience different ecological conditions
adapt to these conditions differently = gradually diverge
degree of divergence depends on how separated they are
and how long they have spent apart
farther and longer time apart = more divergence |
| What are population bottlenecks? how do they affect genetic drift? (3) | drastically reduces the size of a population
eg: environmental disaster, hunting to a point of extinction, habitat destruction
= enhances genetic drift |
| What is the founder effect? how do they affect genetic drift? (3) | a loss of genetic variation when a new population is formed from a small number of individuals form the larger population |
| How does natural selection change a gene pool? | changes the composition of a gene pool because of different selective environmental pressures
eg: a lizard only eating green beetles = more brown beetles |
| What is speciation? | when populations of a species can't interbreed and produce offspring |
| What to the evidence for evolution include? (4) fhsg | fossil record
homologous structures
selective breeding
geographical distribution of organisms |
| What is the limitation to using a fossil record? | fossilization needs a rare set of circumstances = gaps in the record |
| What are transitional fossils? | shows the forms in between which happened to show a connections between species
it demonstrates common traits in the ancestor and descendants
eg: archaeopteryx (links dinosaurs to birds) |
| What are homologous structures? | a structure that different species has but is used in different ways
they show divergent evolution by adaptive radiation
= show common ancestry
more similar = closely related
eg: pentadactyl limb in vertebrates (5 digit limbs) |
| which species can the pentadactyl limb be seen in ? | man, horse, whale, turtle, frog, bird |
| What is adaptive radiation? | rapid evolutionary diversification when members of a species live in niches with different conditions
= they adapt in response to the selective pressures
eg: different beak shapes in darwin's finches |
| What is an example of evolution? (moths) | peppered moths had 2 forms white and black
in an unpolluted environments the trees has pale lichen = camo for the lighter moth
in a polluted environment the soot blackened the bark and killed the lichen = camo for the dark moth
= after the industrial revolution the population of white moths decreased |
