Patterns of inheritance Flashcards
What is allopatric speciation
When a population becomes isolated through geographical isolation and natural selection.
- physical barrier separates two populations of same species
- different climates create different selection pressures
- different alleles are selected for and selected against
- mutations take place independently in each population
- eventually the two populations would of changed so much that they won’t be able to reproduce to produce fertile young
Reproductive isolation is when the changes in alleles and phenotypes of two populations prevent them from successfully breeding, what do these changes include?
- seasonal changes - individuals from same population develop different flowering/mating seasons or become sexually active at different times of the year
- mechanical changes - changes in reproductive organs which prevents successful mating
- behavioural changes - group of individuals develop courtship behaviour that isn’t attractive to main population
What is sympatric speciation
Random mutations occur resulting in changes that prevents successful breeding. Does not involve geographical isolation
Give an example of sympatric speciation
Mutations can occur that increase the number of chromosomes, this is known as polyploidy - means the individual can’t reproduce to give fertile young , if present in diploid population will become reproductively isolated
What is meant by a gene pool
The complete range of alleles present in a population
Give 3 examples of selection pressures
Predation, disease, competition
Outline the process of evolution by natural selection
Individuals of the same species vary due to different alleles created by mutations.
Selection pressures create a struggle for survival
Due to variation some individuals are better adapted than others
Individuals with advantageous alleles are more likely to survive, reproduce and pass the allele to its offspring
Overtime there is a greater proportion of the advantageous allele in the next generation.
What is stabilising selection, what is its effect on the range of phenotypes
When environment isn’t changing, individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
This reduces the range of possible phenotypes as the average phenotype is favoured
What is directional selection
When there is a change in environment, individuals with alleles for characteristics of one extreme type are more likely to survive and reproduce
What is disruptive selection
Disruptive selection produces a population that has two extreme versions of a trait as the dominant phenotype
Disruptive selections are called such because they favor both extreme phenotypes of a trait. This increases diversity in the population, rather than making it more homogenous.
What is the difference between directional and disruptive selection
The difference between directional and disruptive selection is that directional selection favors only one extreme version of a trait and disruptive selection favors both opposite extreme versions of a trait.
What is genetic drift
When chance dictates which alleles are passed on. For example by chance allele for one genotype B is passed on to offspring more often than others. Therefore the number of individuals with that genotype increases
What is the effect of genetic drift on population size
The effect of genetic drift is greater on a smaller population where chance has greater influence.
Does genetic drift have a small or large effect on a genetic bottle neck
Large
What is a genetic bottleneck
An event (natural disaster) that causes a big reduction in a population size, leading to a reduction in the gene pool
