10.3- gene pools and speciation Flashcards
what does a gene pool consist of?
all the genes and their different alleles, present in an interbreeding population
how does a gene pool fit into the definition for a species?
species are groups of potentially interbreeding populations, with a common gene pool that is reproductively isolated from other species.
how would it be possible for multiple gene pools to exist for the same species?
if some populations are geographically isolated
what does evolution require?
that allele frequency’s change with time in populations
define evolution
the cumulative change in the heritable characteristics of a population over time
give 4 reasons for evolution
- mutations introducing new alleles
- barriers to gene flow emerging between different populations
- if a population is small, random events can significantly impact allele frequency
- selection pressures favouring the reproduction of some varieties over others
give 3 types of natural selection
- directional
- stabilising
- disruptive
describe stabilising selection
selection pressures act to remove extreme varieties
- eg average birth weights of human babies are favoured over low or high birth weight
describe disruptive selection
selection pressures act to remove intermediate varieties, favouring the extremes
describe directional selection
the population changes as one extreme of a range of variation is better adapted.
state the 3 categories of reproductive isolation
- temporal
- behavioural
- geographic
define speciation
the formation of a new species by the splitting of an existing population
state the difference between allopatric and sympatric speciation
allopatric; the result of geographic separation of populations//isolation of gene pools
sympatric; when speciation occurs within the same geographic area (either behavioural or temporal)
give an example of behavioural speciation
when closely related individuals differ in their courtship behaviour, so are only successful in attracting members of their own population
give an example of temporal speciation
populations may mate or flower at different seasons or times of day
different populations have
different allele frequencies
state the 2 theories about the pace of evolutionary change
- gradualism in speciation
- punctuated equilibrium
describe gradualism
- the idea that species slowly change through a long sequence of continuous intermediate forms
- confronted by gaps in fossil record- this as explained as imperfections in the fossil record
describe punctuated equilibrium
- holds that long periods of relative stability in a species are ‘punctuated’ by periods of rapid, abrupt evolution
- gaps in fossil record may mot be gaps at all, as there was no sequence of intermediate forms
why may rapid change be much more common in prokaryotes and insects?
these organisms have short generation times
what is polyploidy?
a condition whereby an organism has more than two complete sets of homologous chromosomes in all cells (i.e. > diploid)
how does polyploidy lead to sympatric speciation?
- chromosomes duplicate in preparation for meiosis but then meiosis doesn’t occur
- result is a diploid gamete that when fused with a haploid gamete produces a fertile offspring
- organism is now reproductively isolated from the original population, and can only self-pollinate or mate with other polyploid plants
why is polyploidy far more common in plant species than animal species?
Polyploidy is far more common in plant species which lack separate sexes and are capable of self-pollination
Polyploidy is very rare in animal species due to the consequences of having extra allele copies of every gene
give an example of an organism that has frequently encountered polyploidy
species of angiosperms = flowering plants such as the Allium genus
many species of Allium reproduce asexually and polyploidy may confer an advantage over diploidy under certain selection pressures
