Microevolution

Microevolution

- Population genetics

• how the process occurs

• evolutionary change on a small scale ( population/species level )

Macroevolution

• History

• Evolution on the grand scale (above species level)

• The results of the accumulation of Microevolution are changes over time

Evolution as change in allele frequency

Change in allele frequencies within a population’s gene pool over generations,

Gene

Sections of DNA that codes for specific proteins / traits

Allele

A specific version of the gene , variations of the trait, like eye colour

Gene pool

Sum of all alleles at all loci in a population

Genotype

inherited genetic code (DNA)

Phenotype

observable traits resulting from the genotype

Phenotypic plasticity: Quantitative

Characters of individuals in a population can differ in small incremental ways ( continuous) ex height, weight

Are measurable = quantifiable

Phenotypic plasticity: Qualitative

Characteristics with discrete states

Either one or another ex color

Natural Selection

Mechanism of evolution where organisms better adapted to their environment survive and reproduce more successfully, passing down advantageous heritable traits to their offspring resulting to gradual changes (adaptation) in a population over generations

Sexual Selection

Individuals of one sec with certain trait variants have an advantage in competition for mating with members of the opposite sex over individuals of the same sex without those traits

Directional Selection

A type of natural selection in which extreme phenotype becomes more frequent

Stabilizing Selection

when selection acts against extreme phenotypes, favouring the average phenotype

Disruptive Selection

when selection acts towards one extreme phenotypes, disfavouring the average

Artificial Selection

Individuals with certain trait variants are selected by humans to survive and reproduce instead of individuals without those trait variants

Non-random mating

Genotype frequencies can be altered but not allele frequencies

• allele frequencies stay the same , debatable whether it counts

Assortative mating

Preference for similar genotypes or phenotypes

Disassortative mating

Preference for different genotypes or phenotypes

Gene Flow

Movement of alleles among populations

• movement of genetic material (alleles) between different populations, introducing new variations and increasing genetic diversity ( new alleles) can decrease variation between populations acting against divergence and speciation

Genetic Drift

• Random change in allele frequencies

• Doesn’t lead to adaptation

• Can lead to loss of genetic variation within populations

• Can cause alleles to become fixed

• Significant evolutionary force in small populations ( effect decreases in increasing population size)

Genetic Drift : Founder Effect

A small number of individuals leave a large population to colonize a new area and bring with them only a small amount of genetic variation

Genetic Drift: Population Bottleneck

A reduction in genetic diversity in a population due to large reduction in population size

Mutations

• change to the DNA sequence

• Spontaneous heritable variation in DNA

• Rare events, significant over longer time scales

• Can also be caused by radiation, hazardous chemicals, environmental factors

• most mutations are deleterious and so harmful to organisms

Genetic Equilibrium

Set of conditions under which allele and genotype frequencies do not change over the generations

1. No selection

2. No mutation

3. No Migration

4. Large population

5. Random Mating

Conditions met = Microevolution does not occur

Conditions not met = Microevolution is occurring

Genetic Variation

Diversity in DNA sequence among individuals in a population , raw material of Microevolution

Sources : Production of new alleles & rearrangement of existing alleles into new combos

Evolvability

Probability that some individuals in a population will have advantageous traits

Genetic Variation Overall Factors

• more than one phenotype is favoured by selection

• Balance between mutation and selection

• Environment variation

• Genotype by environment interaction

Genetic Variation Mechanism

• mutations ( new alleles)

• Sexual reproduction ( fertilization, recombination)

• Disruptive selection ( only type of selection favouring variation)

• Gene flow ( between populations)

• Diploid ( and recessive alleles relationship)

• Balancing natural selection ( balanced polymorphism)

Diploidy

Presence of two chromosome sets, prevents recessive alleles from leaving populations

Haploidy

single set of unpaired chromosomes , gametes

Recessive Alleles

Gene /trait that only shows if the individual inherits two copies of it / no dominant allele is present

Dominant Alleles

Gene version that express itself with only one copy present, masking the recessive allele in heterozygous individuals

Balancing selection and Balance polymorphism

More than one allele is actively maintained in a population

Natural selection preserves variation when :

• Heterozygotes have higher relative fitness

• When different alleles are favoured in different environments

• When the rarity of a phenotype provides a selective advantage

= balanced polymorphism

Heterozygote advantage

Higher relative fitness of heterozygous over homozygous genotypes

Selectively favoured if homozygous are selected against

Frequency dependent selection positive

Does not favour genetic variation

Trait fitness increases as it becomes more common in a population, favouring common phenotypes

Frequency dependent selection negative

Rare genotype has advantage as they have higher relative fitness than common phenotypes

Favour genetic variation