natural selection and speciation Flashcards
stabilising selection
- response to STABLE environment
- mode stays same, sd falls - population graph gets narrower and taller as selection against mutation takes place
- eg. birth weight
bottleneck event
- when a population is reduced to a few breeding individuals ∴ much narrower gene pool
- drastic reduction in population
directional selection
- response to CHANGE in environment
- eg. poison used and resistant individuals start to occur
- phenotypes shift in one direction and one aspect of a trait is emphasised (curve shifts right or left)
disruptive/diversifying selection
- response to FLUCTUATING environment
- favours 2 extremes of a trait at expense of intermediate forms
- middle of curve is eliminated and 2 peaks form either side of it
- eg. rock pocket mouse
prezygotic barrier
those which prevent fertilisation from happeneing
postzygotic barrier
fertilisation may occur but any offspring are either not viable or are sterile
eg. prezygotic barrier (3)
- seasonal isolation
- behavioural isolation
- mechanical incompatibility
eg. postzygotic barrier (2)
- hybrid inviability
- hybrid sterility
allopatric speciation
between 2 geographically isolated populations - gene pool physically separated ∴ separate populations evolve independently
sympatric speciation
organisms in the same area become separated into 2+ reproductively isolated groups
variation
difference in characteristics shown by organisms belonging to the same natural population or species
discontinuous variation
when you have or haven’t got a feature - 2 options
eg. blood group
continuous variation
characteristics on a gradient from one extreme to the other - influenced by polygenes and environmental factors
causes of variation (4)
all lead too…
1) crossing over of alleles during mitosis
2) independent segregation of chromosomes (Meiosis I)
3) random fusion of gametes
4) mutations in DNA
… gene reshuffling ∴ variation
selection
process by which organisms better adapted to the environment survive and reproduce and those not so well adapted fail to reproduce or die
genetic drift
a change In the gene pool due to chance
founder effect
new colony started by a few members of the original populations, reducing genetic variation ∴ may lead to speciation
isolating mechanism
barrier preventing gene exchange
point mutation
change in base sequence at a single base in the gene - single base deleted, substituted or inserted
stem cells
unspecialised cells which can develop into other types of cell
totipotent stem cells
can specialise into ANY body cell, including placenta
pluripotent stem cells
can specialise into any body cell, but NOT placenta
multipotent stem cells
present in adult mammals - able to specialise into a few different types of cell
unipotent stem cells
present in adult mammals - able to specialise into only one type of cell
how do stem cells become specialised?
during development they only transcribe and translate part of their DNA, depending on conditions they are in, causing some genes to be expressed and others not to be
iPS cells
induced pluripotent cells
how are iPS cells made
in lab - infecting cells with specially-modified virus which has genes coding for transcription factors within its DNA - genes are passed to the cell’s DNA meaning that the cell can produce the transcription factors
stem cell treatments (currently)
bone marrow transplant - to replace faulty bone marrow - treat leukaemia
future stem cell therapies (5)
- spinal cord injuries
- heart disease and damage caused by heart attacks
- bladder conditions
- respiratory diseases
- organ transplants
how can transcription factors reprogram cells to form iPS cells
- attach to promoter region of gene
- stimulate/prevent binding of RNA polymerase so that transcription does/doesnt occur
transcription factors
proteins that control rate of protein synthesis by switching genes on and off
transcription factors act as…
activators
repressors
how to transcription factors work?
- factors binds to promoter region
- rna polymerase is complimentary and therefore binds to region, activating it
- gene then switched on
- transcription can occur
proto-oncogenes
regulate stages in mitosis - stimulate cell division/growth
tumour supressor genes
prevent tumours
mutation type in proto-oncogenes
gain of function mutation
mutation type in tumour supressor genes
loss of function mutation
metastisis
travel in bloodstream + affect other tissues and spreads
why does genetic drift occur faster in smaller populations
as relatively few individuals = relatively small gene pool = less genetic diversity therefore any mutation will quickly affect members of population because frequency is relatively high (in large pops effect is diluted)
competition
when 2+ individuals share any resource that is insufficient to supply all requirements fully
infraspecific comp
between 2 members of the same species
interspecific comp
between 2 members of different species
competitive exclusion principle
- overall message?
population of species with competitive advantage will gradually increase in size and the other one will diminish - if conditions remain the same, one species will be completely removed
- no 2 species can occupy the same niche indefinitely when resources are limited
genome
all genetic material (alleles) in an organism
proteome
all the proteins produced by the genome (controlled by transcription factors)
