Mechanisms Of Change Flashcards
What is a gene pool
The sum of genes in a population at a particular time
What is the allele frequency
Proportion of particular allele in a population at a particular time
What is the definition of genome
All the DNA of an individual
What is the definition of Hardy-Weinberg equilibrium
Amount of genetic variation in population will remain constant from one generation to the next in the absence of disturbing factors
What is the Hardy-Weinberg equation for allele frequency
p + q = 1
Where p is the dominant and q is the recessive
What is the Hardy-Weinberg equation for genotype frequency
p^2 + 2pq + q^2 = 1
p^2 = AA, 2pq = Aa, q^2 = aa
Why is a population genetically variable
Mutation
Meiosis
Sexual reproduction
Why do meiosis and sexual reproduction cause genetic variation
Independent assortment
Crossing over
Random process
What is variability persevered by
Diploidy
Heterozygotes shelter rare recessive alleles
Describe a population bottleneck
Event drastically reduces the size of a population
Decrease in gene pool so many alleles lost
Low level of genetic diversity
Face higher level of genetic drift
Describe genetic drift
Random fluctuations of gene variants
Alleles increase and decrease by chance over time
Continues until allele lost of only one allele present
Decrease in genetic diversity
Can cause new population to be genetically distinct from original
Describe the conditions for Hardy-Weinberg equilibrium (5)
Large breeding population Random mating No change in allergic frequency due to mutation No immigration or emigration No natural selection
What are the problems with the Hardy-Weinberg equilibrium
Describes ideal state
Disruptive forces commonly occur in nature and this equilibrium rarely applies in reality
What is a point mutation
Mutation that affects one base
Substitution or deletion of a single base
Describe substitution mutation
One base replaced by another
May mean diff polypeptide
Describe deletion mutation
One base deleted
So all triplets altered
Frame shift
Protein may be shortened if stop codon produced earlier
What causes chromosome mutation
Chromosomes fail to separate during meiosis
Describe aneuploidy
One chromosome only fails to separate
Eg Down’s syndrome and turners syndrome
Describe polyploidy
Whole set of chromosomes fail to separate
Individual has 3+ sets of chromosomes rather than 2
Describe how mutagens cause mutation
Chemicals which react with bases and changes their characteristics thus causing them to pair wrongly
May be incorporated into DNA
May take place of base
May slip between nucleotides
How can radiation cause mutation
Can damage DNA
Alter base structure or backbone
Describe selection
Process operating on genetic variation in a population
Leads to the differential perpetuation of alleles to subsequent generations involving both survival and reproduction
Describe survival of the fittest
Alleles that are better adapted survive and reproduce more successfully
What is meant by the phrase struggle for existence
Competition for resources
What is meant by an organisms “fitness”
Measure if features that allow the organism to be adapted to its environment
What are the key points if selection (6)
Acts on a population Environmentally dependent Basis of variation must be genetic Edits genetically inheritable features Selection favours fittest Differential reproductive success - better adapted more likely to survive
Describe stabilising selection
Environmental conditions largely unchanging
Acts against extremes
Does not lead to evolution
Maintains adaptive norm
Draw the graphical change in stabilising selection
See notes
Describe directional selection
Changing environment conditions Some extremes have a selective advantage They survive and reproduce Change in genetic composition of population Leads to evolution
Draw the graphical change for directional selection
See notes
What does polymorphism mean
Presence of 2 or more distinct forms in a population
What is apostatic selection
Different forms maintained
Predator hunts most common
What does speciation mean
Evolution of a new species from ancestral species
What is a species
Group of organisms which can interbreed to produce fertile offspring
They are reproductively isolated from other species
What is allopatric speciation
Evolution of a new species
Due to geographical isolation
Describe the process of allopatric speciation
- Ancestral species expands to new locations
Regular gene flow in gene pool - Physical barrier isolates populations geographically
Gene flow with ancestral population prevented - 2 populations subject to different selection pressures
- 2 populations diverge genetically
If still capable of interbreeding then it is not a new species
Of they can no longer interbreed then a new species has evolved
What happens during interspecific competition
One species eliminates the other
Or
Both evolve further so there is niche divergence
