Chapter 23 Flashcards
Microevolution
Evolution at its smallest scale
Focus on the change in allelic frequencies
3 Mechanisms that cause change in allele freqencies
Genetic Drift- Random change in a population
Gene Flow- Transfer of Alleles between different populations
Natural Selection- Favoring of beneficial trait
Discrete Characters
Characteristics that can be distinctly chosen. Often determined by a single gene locus with different alleles
Quantitative Characters
Characteristics that vary along a continuum. Results from the influence of two or more genes on a phenotypic characteristic
Measuring Genetic Variation
- Measure it through the whole gene level (gene variability)
- Molecular level of DNA through nucleotide variability
Cline
This is a variation of a characteristic across a region. Provides an example of natural selection because organisms living in different environments have to adapt differently
Source of New Alleles
Mutation
Point Mutation
A mutation in which only one base is changed. Often point mutations have no effect is they don’t change the shape/function of amino acids
Translocation
When part of a chromosome is taken and placed on another chromosome. Results in the linking of new DNA
Gene duplication
This occurs when errors happen such as DNA replication slipping, unequal crossing during meiosis.
Duplication of large portions of the chromosome are often harmul, but this allows for this duplication in many future generations, increased genome more loci, more mutations more functions
Mixing of Alleles
-Independant assortment of chromosomes, crossing over, and fertilization
homologous chromosomes cross some of their DNA to eachother
Alleles randomly distributed into different gametes
-Organisms with different alleles mate with eachother
Population
A group of individuals that are the same species, live in the same region, interbreed and produce viable offspring
Gene Pool
A collection of all the alleles from all the loci from all the individuals in the population
Fixed Allele
When there is only one allele that exists for a locus in a population. All individuals are homozygous for this allele
Hardy Weinberg Principle
If the frequency of alleles remains constant through many generations then the population is not evolving. Only in the case of Mendelian segregation and recombination
Conditions for the Hardy Weinberg Principle
- No mutations- they modify the gene pool
- Random Mating- If there is preferential mating, the allele frequencies change
- No Natural Selection- Makes one allele favorable over the other
- Extremely Large Population- Small populations increase chance of genetic drift
- No gene Flow- Migration causes fluctuating allel frequencies
Hardy- Weinberg Equation
p^2+ 2pq + q^2
p- Dominant Allele
q- Recessive allele
Natural Selection
Natural selection changes the allele frequency because it favors the alleles that help the organism survive. Increases favorable allele
Genetic Drift
The process of a chance event that causes alleles to fluctuate unpredictably
Gene Flow
The flowing of alleles into and out of the population. Makes populations more similar
Founder Effect
When a small group of a larger population becomes isolated and forms a new population. This causes a different gene pool from original population- One form of genetic drift
Bottleneck Effect
When a severe drop in the population occurs. This allows one allele frequency to increase, or to be completely taken out of the population. Then there is little genetic variation in future generation- Genetic Drift
Relative Fitness
the contribution an individual mkaes to the genepool to the next generation- The number of beneficial alleles the organism has to pass down to the next generation
Stabilizing Selection
When extreme alleles are unfavorable and so their frequencies decreased while the intermediate is found more favorable. - Narrowed Bellcurve
Directional Selection
This is when an extreme allele is found favorable and the whole population then moves to have this allele and the bell curve is shifted over
Disruptive Selection
This is when two different alleles on extremes of the continuum are found favorable and the frequencies of both alleles increase, while the intermediate decreases- Through this speciation can occur
Sexual Dimorphism
Effect if sexual selection
Where the male and female physical appearances look increasingly different (size color behavior)
Intrasexual Selection
This is competition of individuals within the same sex
A male might guard a females from other males, thus preventing other males from mating with them
Intersexual Selection
Females are able to pick which males they mate with and they choose the ones with the healthiest genes
Preservation of Genetic Variation
- Natural selection does not eliminate variation because there are two mates that form an individual and many recessive alleles are hidden and therefore not eliminated from natural selection
- Balancing selection also preserves variety, when two alleles are thought to be advantageous
Heterozygous Advantage
This is where gene loci have greater advantage in heterozygous individuals than homozygous individuals
4 Reasons why Natural Selection Does Not Produce Perfect Organisms
- Natural selection can only make certain alleles more favorable than others. CANNOT CREATE ALLELES
- Natural selection can only work on the population body structure, cannot form new structure
- Adaptations are only compromises between different factors, not perfect solution
- Genetic Drift, Genetic flow and changing environments are constantly affecting natural selection
