2.6 - variation + evolution Flashcards
what factors produce variation between individuals
- genetic
- environmental
name the types of variation
- continuous + discontinuous
- heritable + non-heritable
what’s discontinuous variation
- type of variation that can be categorised, e.g: blood group
- characteristic can only appearing discrete values
- influenced by one or two genes + environmental factors have little effect on
what’s continuous variation
- type of variation that can’t be categorised, e.g: height
- produces continuous range in which a characteristic can take any value
- influenced by multiple genes + is often significantly affected by environmental factors
compare heritable + non-heritable variation
heritable - genetic differences between individuals
non-heritable - acquired differences in phenotypes of individuals that can’t be inherited
what’s evolution
- change in allele frequencies in gene pool of population over time
- occurs due to natural selection
how does natural selection cause change in allele frequencies over generations
organisms w/ advantageous characteristics are more likely to survive + pass their favourable alleles to offspring
frequency of unfavourable alleles decreases
what are selection pressures
- environmental factors that drive evolution by natural selection + limit population sizes
- can change frequency of alleles in population
give examples of selection pressures
- predation
- disease
- competition (for food, habitats, mates)
- environmental conditions, e.g: temperatures
how can allele frequencies be expressed
as percentage or proportion of total number of all alleles for that gene
state the 2 types of competition
- interspecific
- intraspecific
what’s interspecific competition
type of condition that takes place between members of different species
what’s intraspecific competition
type of competition that takes place between members of same species
define gene pool
all of the diff versions of genes (alleles) in individuals that make up a population
what’s genetic drift
variations in allele frequencies in small populations due to chance (rather than as a result of selection pressures)
what’s meant by the founder effect
when small number of individuals become isolated, forming new population w/ limited gene pool
allele frequencies not reflective of og population
what’s the hardy-weinberg principle
model that allows estimation of frequency of alleles in population, as well as whether allele frequency is changing over time
state the assumptions made by the hardy-weinberg principle
- no mutations occur to create new alleles
- no migration in/out of populations
- no selection, alleles all equally passed on to next generation
- random mating
- large population
explain the hardy-weinberg equation for calculating allele frequency
frequencies of each allele for characteristic must add up to 1, giving the equation: p + q = 1
p = frequency of dominant allele
q = frequency of recessive allele
explain the hardy-weinberg equation for calculating genotype frequency
frequencies of each genotype for characteristic must ad up to 1, giving equation: p^2 + 2pq + q^2 = 1
p^2 = frequency of homozygous dominant
2pq = frequency of heterozygous
q^2 = frequency of homozygous recessive
define speciation
formation of new species due to evolution of 2 reproductively separated populations
why may speciation occur
- genetic drift in isolated population
- founder effect
- natural selection
what are the 2 types of speciation
- allopatric speciation
- sympatric speciation
what is allopatric speciation
occurs when 2 populations become geographically isolated
what is sympatric speciation
occurs when 2 populations within same area become reproductively isolated
outline geographical isolation
physical barrer (e.g: river or mountain) separates 2 populations of the same species
name the potential isolation mechanisms in sympatric speciation
- morphological isolation
- seasonal isolation
- behavioural isolation
- gametic isolation
- hybrid sterility
- hybrid inviability
what’s morphological isolation
reproductive isolation of 2 populations due to incompatibility of reproductive systems
what’s behavioural isolation
reproductive isolation of 2 populations due to differences in behaviour (e.g: diff mating rituals)
describe seasonal isolation
reproductive isolation of 2 populations due to differences in their breeding seasons
describe hybrid inviability
- pos-zygote barrier
- successful fertilisation but embryo can’t develop into living organsim
what’s hybrid sterility
formation of sterile offspring from reproduction of individuals of different species
why may reproduction of individuals of different species produce sterile offspring
chromosome sets from each parent differ so can’t pair up during meiosis
give examples of a sterile hybrid + a fertile hybrid
sterile - mule
fertile - wheat
what is gametic isolation
- prezygotic barrier
- successful fertilisation doesn’t occur
what is gametic isolation
- prezygotic barrier
- successful fertilisation doesn’t occur
