variation and evolution Flashcards
what is continuous variation?
controlled by a number of genes
character shows gradiation from one extreme to another
what is discontinuous variation?
controlled by a single gene
no intermediate forms
what is heritable variation?
results from genetic change due to sexual reproduction
mixing of 2 different parental genotypes in cross fertilisation (random assortment of chromosomes and crossing over)
what is non-heritable variation?
environmental influences that determine phenotypic variation (diet/temperature/light/exercise)
how can a gene pool remain stable over time?
if the environment stays stable
what happens if there are environmental changes?
some phenotypes will be more advantageous
gene pool will change
certain alleles become more frequent
what is selection?
process by which organisms better adapted to environment survive and breed
better adapted organisms are more likely to pass on their characteristics to succeeding generations
what is selection pressure?
organisms environment exerts selection pressure which determines frequency of allele within gene pool
what is genetic drift?
chance variations in allele frequencies in a population
what do you need for allele frequencies to remain constant from one generation to the next (Hard-Weinberg equilibrium)?
large population (100+)
population is isolated
no selection pressures
reproduction is sexual
no new mutations
organisms are diploid
random mating throughout population
what does p stand for?
frequency of dominant allele
what does q stand for?
frequency of recessive allele
what does p squared stand for?
frequency of homozygous dominant
what does q squared stand for?
frequency of homozygous recessive
what does 2pq stand for?
frequency of heterozygous
what is evolution?
change in average phenotype of a population
what is natural selection?
increased chance of survival and reproduction of organisms with phenotypes suited to their environment
enhances transfer of advantageous alleles from one generation to the next
what is speciation?
formation of new species
what are species?
group of phenotypically similar individuals tat can interbreed to produce fertile offspring
what can cause speciation?
natural selection
mutations
genetic drift in isolated populationsw
what is the founder effect?
loss of genetic variation in new populations established by very small number of individuals from a larger population
how does the founder effect occur?
population isolated in new habitat
founder members of population are a small sample of original population
may have very different allele frequency to original population
may undergo genetic drift§
what is the bottleneck effect?
results from disaster that drastically reduces population size
what is an isolating mechanism?
features of behavior, genetics and morphology
what is a population?
inter-breeding group of species
what are demes?
sub group of population may breed more often with each other than with the rest of the population
how can demes become reproductively isolated?
prevention of reproduction/gene flow between breeding groups within species if isolated for many generations, accumulate different mutations, cannot interbreed
what is pre-zygotic isolation??
gametes are prevented from fusing so zygote never forms
what can cause pre-zygotic isolation?
geographical isolation + allopatric speciation
behavioral isolation + sympatric speciation
morphological/gametic/seasonal isolation
what are seasonal barries?
when breeding season/time of activity of two closely related populations don’t exactly correspond
what are morphological barries?
no longer able to physically mate as genitals are incompatible
what is post-zygotic isolation?
gametes fuse and zygote forms
organism may develop but is sterile
genes of parent species are kept separate and do not merge
what is a hybrid?
offspring of a cross between members of a different species
what is hybrid sterility?
chromosomes are not sufficiently similar so unable to pair at prophase I so gametes cannot form
what happens in plants with hybrid sterility?
asexual reproduction produces colony of sterile hybrids
can undergo mutations to become polyploid so will then become fertile
what is adaptive radiation?
process in which species have all descended from a common ancestor and have over time adapted successfully to their environment
