EEB 309 - Midterm Review

Mutation

A change in an organism’s DNA sequence that can become fixed in a population with selective pressures.

Substitution

This occurs when a mutation becomes fixed in a population with selective pressures.

Site

Refers to a specific position within a DNA, RNA, or protein sequence where a particular nucleotide, amino acid, or other chemical group is located. Each site can be associated with various biological functions, interactions, or structural features.

Character

This can be a morphological trait or a specific DNA sequence that can be studied in regards to phenologies.

Allele

A specific version of a gene on a locus.

Genotype

The underlying allele pair that codes for a phenotype. AA or aa are a genotype.

Neutral

Some mutations are considered this, in which there are no selective disadvantages or advantages to an organism who possesses them. In other words, fitness is not affected.

Positive Selection

A mutation or allele is advantageous and increases the fitness of an organism. This leads to the increased survival and reproduction of a population with these traits.

Negative/Purifying Selection

A mutation or allele is disadvantageous and decreases the fitness of an organism. This eliminates traits over time from a population.

Variance

This describes the differentials of phenotypes dependent upon genetic and environmental factors. It is quantifiable and describes how much individuals within a population differ from each other in terms of a particular trait (phenotype).

Additive

Occur when the contributions of alleles to a trait combine in a straightforward manner, meaning that the total phenotypic effect of multiple alleles is the sum of their individual effects. For example, if one allele contributes a certain amount to a trait and another allele contributes a different amount, the total contribution to that trait is simply the sum of the two contributions. They are concerned with genetic factors.

Recessive/Dominant

Alleles can be considered either of these terms. To be “D” does not mean that it is automatically going to be fixed or more advantageous than “R”.

Branch/Node/Tip

“B” refers to the length of a phylogenetic tree. “N” refers to where species have diverged from a common ancestor. “T” refers to the species in focus at the terminal branch.

Drift

This occurs when there are events such as the founder effect or bottleneck effect that change the frequency of alleles in a population. It is a mechanism of evolution that refers to random changes in allele frequencies within a population over time. These changes can occur due to chance events, particularly in small populations, and can significantly impact the genetic makeup of a population.

Broad Sense Heritability

Big H = VG/VP. It is a measure used in genetics to quantify the proportion of phenotypic variance in a population that can be attributed to genetic variance.

Narrow Sense Heritability

Little h = VA/VP. It is a measure of the proportion of phenotypic variance in a trait that can be attributed to the additive genetic variance among individuals in a population.

Lagerstatten

Means “storage place”. Refers to areas where high resolution fossils have been preserved in large assemblages. Ex. Burgess Shale

Molecular Clock

A method used in evolutionary biology to estimate the time of divergence between species or the timing of evolutionary events based on the mutation rates of biomolecules, particularly DNA, RNA, or proteins. The underlying principle is that genetic mutations accumulate at relatively constant rates over time, which can be used to measure the time since two species shared a common ancestor.

Phylogenetically Independent Contrasts

A statistical method used in evolutionary biology and comparative analysis to account for the non-independence of traits due to shared evolutionary history. This approach is particularly important when analyzing traits across species that share a common ancestor, as it helps to avoid biases that may arise from the shared evolutionary relationships among species.

Ancestral State

Describes the state of a trait in the common ancestor species or group of species.

Response to Selection

This is a variable in the equation R=h²S. It refers to the difference between the average from the original population to the average after time has passed. Refers to the change in the average phenotype of a population from one generation to the next due to selection pressure. It quantifies how much a trait's average value in a population changes in response to selection.

Selection Differential

This is a variable in the equation R=h²S. It refers to the difference in average phenotype in the original population vs. right after selection has occurred.

Heterozygote Advantage

This occurs when the Aa genotype has a more extreme phenotype than either the AA or aa genotypes.

Allele Frequency

Allele frequency refers to the proportion of an allele in a population. Changes in this over time in a population refers to evolution.