allopatric speciation
where a species becomes two separate species after being geographically isolated by a physical barrier
why does speciation occur after geographic isolation
- difference in initial gene pool
- potential for genetic drift
- faced with different selection pressures
sympatric speciation
where a species arises from an ancestral species that continues to live in the same geographic area
anagenesis
when an entire species gradually evolves into a new, different species with the new species completely replacing the old one
cladogenesis
when one species splits into two or more species
temporal isolation
the timing of reproduction difference in timing example the species are n to ready to reproduce at the same time
behavioural isolation
if its a closely related species if they don’t do things In the correct sequence or offer the wrong gift and its rituals aren’t followed she will shut it down
haitat isolation
example - the two species living in separate habitats likelihood of species seeing each other is very low
what prevents species from interbreeding
reproductive isolating mechanisms and prezygotic and postzygotic barriers
mechanical isolation
parts don’t fit together
reduced hybrid viability
they get to the juvenile stage but not to the sexual reproduction stage
reduced hybrid fertility
they failed to produce functional gametes offspring of hybrids have reduced viability or fertility
if all alleles in a population are homozygous for an allele the allele is said to be fixed ( having or existing in only one form
monomorphic
hw is disrupted by
- mutation
- mate selection
- migration
- genetic drift
allelic frequencies remain constant if there is
- no mutation
- no migration
- no mate selection
- no genetic drift
- non natural selection
polypoidy results in instant
sympatric speciation there is an extra chromosome result
punctuated equlibrium model
a new species changes most as it buds from a parent species
how can polypoidy cause reproductive isolation
producing a mismatch in chromosome numbers between a polyploid organism and its diploid parents, leading to sterile or low-fitness offspring during interbreeding.
