d4.1 natural selection Flashcards
why does there need to be a selection pressure
population always tend to produce more than the environment can support
struggle for survival [4]
- food
- predation
- parasitism
- disease
biotic factors [3]
- struggle survival
- competition for mates
- competition for space
what is population dependent on
selection pressures
abiotic factors
population independent
abiotic factor eg
temperature
how to get variation between number of species
- random mutation
- sexual reproduction
how does variation occur during random mutation [2]
- dna replication
- viral infection
mate selection
females of some species will select male mates on an exaggerated trait
how does variation occur in sexual reproduction [2]
- meiosis- crossing over (prophase i) and random assortment of chromosomes (metaphase i)
- random fertilisaiton
mate selection eg
peacocks
how does mate selection affect their traits
the exaggerated traits will become more exaggerated until it hinders their survival
gene pod
consists of all the gene and their alleles present in a population
allele frequency eg
alcohol dehydrogenase breaks down alcohol in the liver- linked with rice cultivation and sake production
Weismann’s germ plasm theory
natural selection drives allele frequency changes in a gene pool
what gets passed on according to the germ plasm theory
germ plasm
things in the somatic cells dont get passed on
3 types of natural selection
- directional selection
- stabilising selection
- disruptive selection
directional selection
individuals that display a more extreme of a trait have greater fitness than individuals with an average form of the trait
directional selection change in shape
change mean to left or right
natural selection distribution
normal distribution- most in normal range
directional selection eg
beak of gallapagos
stabilising selection
individuals with the average form of a trait have the highest fitness
- wont survive with too little or too much
stabilising selection change in shape
higher in the middle
narrower than normal distribution
disruptive selection
individuals with either extreme variation of a trait have a greater fitness than individuals with the average form of the trait
disruptive selection eg
salmon
hooknoses- bigger so can fight
jack- small so can sneak in
disruptive selection change in shape
mean decrease
‘m’ shape
hardy-weinburg equilibrium
used to determine if a population is in genetic equilibrium
hardy-weinberg conditions that must be maintained for a population to be in genetic equilibrium [5]
- no mutation in gene
- mating is random
- no immigration or emigration
- population is large enough to prevent allele frequencies changing due to change
- natural selection does not favour one phenotype over another
why is the condition no mutation
so alleles are not changed and no new alleles are being generated
why does mating need to be random
no phenotype preferentially mates with another particular phenotype
why can there be no immigration or emigration
constant allele frequencies
