10 - Variation and Evolution (C2) Flashcards
What are the 4 types of selection pressures?
- Environment e.g. drought
- Intraspecific competition e.g. for food
- Interspecific competition e.g. predation
- Human factors e.g. deforestation
What are 2 examples of natural selection?
- Camouflage
- Mimicry (e.g. hover flies looking like wasps)
What is discontinuous variation?
Characteristics that are clear-cut and controlled by a single gene
What is continuous variation?
- Characteristic within a population that shows a gradation from one extreme to another
- Controlled by a number of genes
What is the definition of a gene pool?
The total of all alleles for all of the genes in a population
What can selection pressures affect?
- The frequency of alleles within the gene pool
- The survival of different phenotypes in a population
What does the Hardy-Weinberg equation measure?
Allele frequency
What does the Hardy-Weinberg principle state?
That the frequencies of dominant and recessive alleles and genotypes will remain constant if certain conditions remain true
What conditions must be true in the Hardy-Weinberg principle?
- Large population
- No selection for or against any phenotype
- Random mating throughout population
- No mutations
- Population is isolated e.g. no immigration or emigration
What is the Hardy-Weinberg equation and what do the letters stand for?
p2 + 2pq + q2 = 1 p = frequency of dominant allele q = frequency of recessive allele p + q = 1 p2 = frequency of homozygous dominant 2pq = frequency of heterozygous q2 = frequency of homozygous recessive
What can cause speciation?
- Genetic drift in isolated population
- The founder effect of disproportionate allele frequencies in small populations
- Natural selection
When does allopatric speciation occur?
When populations occupy different environments
When does sympatric speciation occur?
When populations are reproductively isolated within the same environment
When does behavioural isolation occur?
When 2 different species or populations evolve courtship displays which are essential for successful mating
When does ecological isolation occur?
When 2 species or populations occupy different habitats within the same environment
When does geographical isolation occur?
When 2 populations occupy 2 different environments which are separated by some physical barrier
When does morphological isolation occur?
When the reproductive structures are physically incompatible
When does seasonal isolation occur?
When 2 or more species or populations live within the same area but are reproductively active at different times
Why is a mule infertile?
It has 63 chromosomes which is an odd number so they can’t form homologous pairs in prophase 1 of meiosis
Why could a male human (46 chromosomes) not breed with a female lion (46 chromosomes)?
They have species specific binding proteins on their sperm and oocyte which don’t correspond
What is the bottleneck effect?
Where the population size is dramatically reduced by a catastrophic event
What is the founder effect?
Where a small number of individuals colonise a new area
What things can change allele frequencies?
- Genetic drift
- Mate selection
- Gene flow
- Natural selection
- Geographical barriers
- Mutations
- Immigration
What is variation caused by?
- Mutation
- Random fertilisation of gametes
- Independent assortment of chromosomes in meiosis
- Crossing over between homologous chromosomes is meiosis
- Environmental influence on gene expression (epigenetics)
What is the definition of variation?
The differences between organisms of the same specie
What is the definition of a selection pressure?
An environmental factor that can alter the frequency of alleles in a population, when it is limiting
What is the definition of genetic drift?
Chance variations in allele frequencies in a population
What is the definition of evolution?
A change in the average phenotype of a population
What are the 3 types of natural selection?
- Stabilising selection - the average phenotype causes the greatest advantage
- Directional selection - an extreme phenotype becomes advantageous
- Disruptive selection - average phenotype is disadvantageous, a lower and higher value have advantages
What are 2 types of reproductive isolation?
- Pre-zygotic - gametes are prevented from fusing so zygote never forms
- Post-zygotic - gametes fuse and zygote forms, but it i s sterile as the species don’t merge
What is a hybrid?
The offspring of a cross between members of different species
