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
Define Degeneracy
More than 1 Condon that codes for the same amino acid
Neutral / silent mutations what are they ?
Mutations are neither harmful nor beneficial to the organism in which they occur. Have no observable phenotypic effect , but can be detected using genome analysis.
May be important in an evolutionary sense.
Block mutations
- how do they occur
- What do they cause
- 4 ways they are described
- some occur as a result of errors in crossing over during meiosis.Mutagens can also cause it
- Cause genetic imbalances which usually disrupt development.
- Described as
- Inversion = Pieces of chromosome are * flipped * so the genes appear in reverse order.
- Translocation = Pieces of chromosome are moved from 1 chromosome into another
- Duplication= Pieces of chromosome are repeated so there are duplicate segments
- Deletion = Pieces of chromosome are * lost* ~Probably has the greatest effect
Mutagens what are they and examples
An agent which cause genetic mutation
- UV light
- Radiation
What is Whole Chromosome Mutations
Due to whole chromosome being “ misplaced “ usually due to a mistake in the process of cell division
A mistake in meiosis is known as non-disjunction.
The 2 forms of non-disjunction mutation and what are they .. ?
Aneuploidy ~ A condition where 1 or more chromosomes are missing from or added to the normal somatic cell chromosome to the normal somatic cell chromosome number.
Polyploidy ~Describes the state of having 3 or more complete sets of chromosomes ( 3N or greater )
NOTE- Is rarely observed in humans, but it is thought to be one of the more common cause of spontaneous abortion
Bottleneck Effect
- how does it occur
- Whats the impact
-occurs when the size of a population is drastically reduced for at least one generation.Could be due to seasonal climatic change or some disaster or disease causes a rapid decrease in the size of a large population.
-The impact is the few survivors that reproduce to give the next generation may by chance be an unrepresentative sample of the gene pool of the original population.
So when the population rebuild , the allele frequencies can be very different from those in the original (pre-disaster) population, and the genetic diversity that is the population’s insurance policy may be greatly reduced.
isolation of genes can occur two ways
- Allopatric speculation - caused by geographic isolation
example- Separation by a river , mountain range , canyons , glacier ,oceans - Sympatric Speciation- Is genetic isolation caused by behaviour , chromosome differences , seasonal behaviour.
Founder Effect
- how does it occur
- Whats the impact
- Occurs when a small no. of individuals may migrate or become isolated from their original population
-This founder population will have a small and probably non-representative sample of alleles from the parent population pool.
As a consequence of this may evolve into a different direction than the parent population
Typically seen in the populations of islands which are colonised by individuals from the mainland population
