genetic makeup of populations Flashcards
Define allele
a variation of the same gene. e.g.) gene = eye colour , Allele= blue, green , hazel
Define Population
the total no. of 1 species in a particular area
May be large and occupy large areas or exist in small pockets e.g.> island
Define species
A group of interbreeding individuals reproductively from other such groups.Often composed of different populations ( often I different habitats ) that are quite distinct
What are differences in species called ?
Races or varieties depending on the degree of reproduction isolation
What is a gene Pool
The sum total of all the genes present in a population at any given time.
Gene pools are subject to processes that alter allele frequencies.This process are … ?
- Mutation -spontaneous mutations can alter allele frequencies and create new alleles
- Gene Flow-Genes can be exchanged with other gene pools as individuals move between them.
- Natural Selection-Pressue against certain alleles combinations may reduce reproductive success.
- Non-random mating-Individuals seek out particular phenotypes with which to mate with.
- Small population + Genetic drift-Alleles may be lost or foxed.
What is genetic Drift ?
What population is it the strongest in ..
Is a mechanism of evolution in which allele frequency within a population change over generations due to chance
- Strong in small populations , may result in a loss of alleles or a rise to 100% however in large population their is little or no genetic drift therefore stable in popn
Whats 4 mechanisms of genetic drift ?
- natural selection
- gene flow
- mutation
- Bottle Neck + Founder effects
What is gene flow
Is the movement of genes into to out of a population ( immigration / emigration ) May gain or lose alleles thru gene flow
How does differences get reduced
What stops gene flow … ?
- Tends to reduce differents because the gene pool becomes more similar
- Barriers
Selective breeding
Humans have controlled the breeding of domesticated animals and plants for centuries this is know as selective breeding.
Involves breeding from individuals with the most desirable phenotypes.
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Define Natural Selection
Populations of sexually reproducing organisms consist of varied individuals with some variants leaving more offsprings than others
The rules of Nature Selection
1- Their is phenotypical variation amongst individuals of the population
2-In changing environments individuals with a favoured phenotype will have an improved chance of surviving and reproducing
3-Over time there is greater chance of offsprings having favoured phenotypes
4-The favoured phenotype (allele frequency will increase if selection pressures do not change)
IN TIME A NEW SPECIES MAY EVOLVE
The no. of factors that cause variation
1- Sexual Reproduction ~crossing over of chromosomes ~random assortment of chromosomes during meiosis ~Combination of gametes ~Random selection of mate 2-Mutation 3-Gene Flow 4-Environment Factors Genetype + Environment = phenotype
Mutation
What are 3 ways .. ?
Some mutations can be fatal , whereas some mutations can bring about a favoured phenotype
- Point / Base mutations
- Block mutation
- Whole chromosome mutation