10.3 - gene pools and speciation Flashcards
What is a gene pool?
- an interbreeding population has groups of the same species in the same place that can breed and have fertile and viable offspring.
- the different alleles of each gene for one species in one population
- because of geographical isolation there can be multiple gene pools for one species
what are allele frequencies?
- Evolution is the change in heritable characteristics of a population over time
- ## In small populations, random events or chance can affect allele frequency
what are the patterns of natural selection?
- selective pressures influence the phenotypes passed on
- There are three patterns of natural selection: directional, stabilising and disruptive selection
what is Stabilising selection?
-selection pressures act to remove extreme varieties for a median e.g. average human birth weights are favoured over low and high birth weights; or median clutch sizes rather than too many or too few offspring/eggs
what is Directional selection?
- where the population changes as one extreme of a range of variation is better adapted e.g. Peppered Moth.
what is Disruptive selection?
- selective pressures act to remove intermediate varieties and favour the extremes e.g. red crossbills. The lower part of the beak is asymmetric and this adaptation means they can get seeds from conifer cones.
- An ancestor with a straight bill would have experienced disruptive selection so they offspring with a bill either crossed to the left or right (both exist as cones hanging from different positions can be accessed by all)
what is Speciation by reproductive isolation?
- Speciation is the formation of a new species when it is split from an existing population that are no longer able to produce viable and fertile offspring
what does a geographical barrier cause?
-allopatric speciation
- eg. cichlids (fish) where annual water level fluctuations due to the rainy or dry seasons can lead to isolation and subject populations to different selective pressures that could result in a new species being formed.
what happens when isolation of gene pools occurs in the same geographical location?
- sympatric speciation
- include behavioural and temporal isolation mechanisms
what is behavioural isolation?
- closely related individuals differ in their courtship behaviours; thus organisms attract only members of their own population
what is Temporal isolation?
- gene pools in the same area is due to different mating or flowering time of the day or seasons
what are Geographical isolation and allele frequencies in humans?
- YALE has the Allele Frequency Database (AlFreD) that contains the frequencies of a variety of human populations
- most human populations aren’t isolated bc of travel ect.
- Laron syndrome is an autosomal recessive disorder where there is a mutation in the growth hormone receptor and results in short stature, increased insulin sensitivity and potential cancer development - popular in jews
what is Gradualism in speciation?
- the idea that species slowly change through a series of intermediate forms
- eg, this suggests that there were various beak sizes, and the intermediate forms had not been identified
- suggests evolutionary change is slow and uniform throughout time
- main idea of paleontology
- the absence of some intermediate forms in the fossil record threw doubt on this theory
what is the Punctuated equilibrium?
- idea that long periods of relative stability (stasis) in species are punctuated by periods of rapid evolution
- though that event like allopatric speciation can lead to rapid speciation
- Rapid changes common in organisms with short generation times like prokaryotes and insects
what is a Polyploidy?
- an organism with more than two sets of chromosomes
- result from hybridization events between different species - but can also originate from the ancestral species
