Variation And Evolution🦋 Flashcards
(42 cards)
What is a gene mutation?
- A random event resulting in a new allele
- Occasionally a mutation provides a new phenotype such that the mutant has a selective advantage over other individuals in a population
- Over many generations, populations change so individuals with the mutant allele become more frequent (micro evolution)
- Evolutionary changes also result in the formation of a higher taxonomic group such as a new genus or class (macro evolution)
What is selection pressure?
- Environmental factors that keep populations in check
- Created by selective agents
- Include disease, competition for resources, predation, lack of light, water or oxygen, changes in temperature
What is a selective advantage?
Organisms that are best adapted to survive these selection pressures
What is a gene pool?
All the alleles of all the genes in a population
What is allele frequency?
- The environment exerts selection pressures, which regulate the frequency of alleles in the gene pool
- Allele frequencies can be expressed as a proportion or a percentage of the total number of copies of all alleles for that gene
What is discontinuous variation?
- One pair of alleles usually controls discontinuous variation
- It is categoric - fits into one of several categories and are not affected by environmental conditions
- Discrete non-overlapping groups mainly cause by single genes
- Not influenced by environment
- Examples include blood groups and earlobe attachment
Continuous variation
- Controlled by a number of different alleles
- If the organism inherits alleles for this characteristic then it may be expressed in their phenotype
- The environment plays a part - an individual may inherit alleles for being tall but if the individual has a poor diet they will not reach their potential height
- Can have any value on a scale between a maximum and minimum
What is heritable variation?
- A variation in the genes in the gametes of an organism will be passed on to the offspring
- Due to different DNA nucleotide sequences or epigenetics
What is non-heritable variation?
- Caused by environmental conditions
- Does not lead to natural selection
- E.g. differences in diet can lead to a large variation in body shape and size within a population of animals, but this variation is not passed onto the next generation because the genes of the organism are not altered
RECAP EVOLUTION NOTES
FROM BIODIVERSITY
Natural selection
- Mutations are important in natural selection - create genetic variation
- Variation leads to some individuals being better adapted to survive in the environment than other individuals - selective advantage
- Organisms with a selective advantage are more likely to survive and reproduce
- By surviving and breeding, they pass in the alleles that give them their selective advantage to their offspring
- Offspring are more likely to survive
- Occurs over a long period of time and results in the characteristics that gave the selective advantage becoming widespread in the population
- Through natural selection the species has evolved
Important aspects of natural selection
•Overproduction - more offspring are produced than are required to replace the parents
•However, over time populations remain relatively stable because of:
-interspecific competition
-intraspecific competition
Industrial melanism - example of natural selection
•Peppered moth is an example polymorphism
•One species has pale wings and one has dark wings
•Increase in allele frequency of black (melanic) forms was linked to air pollution and is called industrial melanism
•This is due to selective predation by birds
•The birds produced the main selection pressure by feeding differentially on moths according to their background
-in unpolluted areas, the pale moth had the selective advantage of not being visible
-in polluted areas, the melanic moth had the selective advantage
•Allele frequency of melanic moths was high in industrialised areas
•Allele frequency of pale moths has increased over time
What is the Hardy-Weinberg principle?
Predicts that the frequency of alleles of one gene in a population will stay the same from generation to generation
What assumptions does the Hardy-Weinberg principle make?
- The population is large (100+ individuals)
- There is no movement of organisms in (immigration) or out (emigration) of the population
- There is random mating between individuals in the population
- All genotypes must have the same reproductive success - no selection for or against any phenotype
- No gene mutation
What is the Hardy-Weinberg equation?
p^2 + 2pq + q^2 = 1
p+q=1
What do the letters in the Hardy-Weinberg equation mean?
- p=frequency of dominant allele A
- q=frequency of recessive allele a
- p^2=frequency of homozygous dominant AA genotype
- q^2=frequency of homozygous recessive aa genotype
- 2pq=frequency of heterozygous Aa genotype
Genetic biodiversity
•Variety of alleles in the gene pool of a population
•Can be assessed by:
-at the population level using Simpson’s diversity index
-at the genetic level by assessing the proportion of polymorphic loci across the species genome
-at the molecular level by DNA fingerprinting and sequencing techniques
What is speciation?
- The evolution of 2 or more new species from a genetically similar population that undergo genetic differentiation and reproductive isolation
- Become morphologically, physiologically and behaviourally different from members of the original species
- No longer able to breed with members of original species to produce fertile offspring
What can cause speciation?
- Genetic drift (random)
- Founder effect (random)
- Genetic bottleneck (random)
- Selection pressures leading to natural selection (not random)
What is genetic drift?
- A change in the gene pool/allele frequency that occurred by chance
- Alleles are also lost by genetic drift and not due to selection pressure
How is genetic drift different from natural selection?
Allele frequency is changed through random chance, not because the allele confers or does not confer a selective advantage
What are the potential impacts of genetic drift?
- May contribute to the extinction of a population or species
- Could lead to production of a new species - important evolutionary mechanism
What is the founder effect?
- A specific type of genetic drift
* Occurs when a small group from a population colonises a new area and forms a new population
