Variation In Generations/ Evolution
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How can gene flow alter allele frequencies?
Genes can be exchanged with other gene pools as individuals move between them
How can natural selection alter allele frequencies?
Selection pressures against certain allele combinations may reduce reproductive success
How can mutations alter allele frequency?
Spontaneous mutations can alter frequencies and create new alleles
How can small population size and genetic drift alter allele frequencies?
In small populations allele frequencies can change randomly from generation to generation, alleles may be lost or fixed
How can non random mating alter allele frequencies?
Individuals seek out a particular phenotype with which to mate
What is a directional process that alters allele frequency?
Some particular alleles are favoured over others
What is genetic drift?
A mechanism of evolution in which allele frequency within a population changes over generations due to chance
What type of population is genetic drift strongest in?
Small populations
Mechanisms of genetic drift include:
• natural selection • gene flow • mutation • bottle neck and founder effects
What could cause a rapid change in allele frequencies within a small population?
A major event eg. disease
What is gene flow?
The movement of genes in or out of a population (immigration or emigration)
What does gene flow result in between different populations?
Reduces differences between populations because the gene pools become more similar
What is another name for random mating?
Non assortive mating
When individuals search out mates that are most like themselves this is known as?
Assortive mating
What must occur for natural selection and evolution to occur?
• there is phenotypical variation • some individuals have a favoured phenotype which improves chances of survival and reproduction • over time there is a greater chance of favoured phenotype offspring being born • the favoured phenotype will increase if selective pressures don’t change • in time a new species may evolve
What are some ways variation can be caused?
• sexual reproduction • mutation • gene flow • environmental factors
How can mutations occur?
• point/ base • block • whole chromosomes
What term is given to mutations that are neither harmful or beneficial?
Neutral or silent
Why are neutral mutations hard to detect?
Because they have little or no change in the phenotype
Why may neutral mutations be important in an evolutionary sense?
Even though they have no adaptive value when it occurs this may not be the case in the future
In what ways do block mutations occur?
• as a result of errors during crossing over in meiosis - mutagens can also cause block mutations
What ways can block mutations be described?
• inversion • translocation • duplication • deletion
What is an inversion block mutation?
Pieces of chromosome are flipped so their genes appear in the reverse order
What is a translocation block mutation?
Pieces of chromosome are moved from one chromosome to another