genetics (evolution) Flashcards
what is variation?
the differences that exist between individuals
what does variation within a species mean?
the individuals can show a range of phenotypes
what causes genetic variation within a species?
mutations
meiosis
random fertilisation
the environment
what type of variation results in evolution?
genetic
what is evolution?
when the frequency of an allele in a population changes over time
what are selection pressure?
environmental factors that limit the population of a species
what is the gene pool?
total number of alleles of all the genes of all individuals of a population during a given time
how does natural selection occur?
1) individuals of the same species vary due to differences in alleles
2) predation, disease and competition create a pressure for survival
3) as individuals vary, some are better adapted to deal with selection pressures than others
4) individual with a phenotype that increases their chance of survival is more likely to survive/reproduce/pass on genes
5) greater proportion of a population inherit beneficial alleles
6) more likely to survive/reproduce/pass on genes
7) frequency of beneficial allele increases across generations
what is stabilising selection?
where individuals with alleles for characteristics towards the middle of the range are most likely to survive and reproduce
occurs when the environment isn’t changing and reduces the range of phenotypes
what is directional selection?
individuals with alleles for a single extreme phenotype are more likely to survive and reproduce
could be in response to an environmental change
what is disruptive selection?
where individuals with alleles for extreme phenotypes at either end of the range are most likely to survive and reproduce
occurs when the environment favours more than one phenotype
what is speciation?
development of a new species from an existing species
when does speciation occur?
members of the same species become reproductively isolated
what is allopatric speciation?
speciation that occurs due to a physical barrier- geographical speciation
what is sympatric speciation?
when a population becomes reproductively isolated without any physical separation
why does geographical isolation lead to allopatric speciation?
experience different conditions on different sides of the geographical barrier
what are the stages of allopatric speciation?
physical barriers stop interbreeding between populations
populations adapt to the new environments
allele frequency and phenotype frequencies change which leads to the development of a new species
why does sympatric speciation occur?
populations become reproductively isolated due to differences in their behaviour
why could sympatric speciation result?
random mutations prevent breeding
what changes could occur as a result of mutations which affects speciation?
seasonal eg) sexually active at different times of the year
mechanical eg) changes in genitalia prevent successful mating
behavioural eg) courtship rituals that aren’t attractive
how can genetic drift lead to evolution?
individuals within a population show variation in their genotypes
the allele for one genotype is passed onto the offspring more often than others by chance
number of individuals with the allele increases
changes in allele frequency in two isolated populations could eventually lead to reproductive isolation/speciation
where does evolution by genetic drift have a greater effect?
in smaller populations where chance has a greater influence
