Biology 2E - The Evolution of Populations and Phylogenies

These flashcards cover key terms and definitions related to population genetics, evolution, and phylogenetic analysis for exam preparation.

Population Genetics

The study of changes in allele frequencies in populations over time.

Genotype

The genetic constitution of an individual, represented by alleles (e.g., AO, BO, AB, OO).

Phenotype

The observable traits of an individual, as influenced by genotype and environment.

Natural Selection

A mechanism of evolution where certain traits increase in frequency due to their advantage in survival and reproduction.

Genetic Drift

Random changes in allele frequencies in a population, often significant in small populations.

Gene Flow

The transfer of alleles or genes from one population to another due to migration.

Mutation

A change in an organism's DNA that can introduce new genetic variation into a population.

Non-random Mating

A mating pattern in which individuals with certain phenotypes or genotypes preferentially mate.

Hardy-Weinberg Equilibrium

A principle stating that allele and genotype frequencies in a population remain constant from generation to generation in the absence of evolutionary influences.

Monophyly

A group that includes a common ancestor and all of its descendants, forming a clade.

What is stabilizing selection? How does it change a characteristic?

Favors intermediate phenotypes, acting against extreme variations. This decreases genetic diversity and maintains the status quo of a trait within a population over time.

What is directional selection? How does it change a characteristic?

Favors one extreme phenotype over others, causing allele frequencies to shift continuously in one direction. This leads to an increase in the proportion of individuals with the favored extreme trait over time.

What is diversifying selection? How does it change a characteristic?

Favors individuals at both extremes of the phenotypic range over intermediate phenotypes. This can lead to the formation of two distinct phenotypic groups within a population and potentially to speciation over time.

How does genetic drift lead to changes in a population’s gene pool over time?

The random fluctuation in allele frequencies from one generation to the next, particularly significant in small populations. It can cause alleles to become more or less common, or even be lost (fixation), regardless of their fitness, thus driving evolutionary change in the gene pool.

What is a genetic bottleneck and how does it lead to changes in a population’s gene pool?

Occurs when a population undergoes a drastic reduction in size due to an event (e.g., natural disaster, disease). The surviving population often has a much-reduced genetic diversity and allele frequencies that may not be representative of the original population, leading to significant and often random changes in the gene pool.

What is gene flow and how does it lead to changes in a population’s gene pool over time?

The transfer of alleles between populations. It can introduce new alleles into a population, change the frequency of existing alleles, or homogenize allele frequencies between populations, thereby altering the gene pool over time.

What are mutations and how do they lead to changes in a population’s gene pool over time?

Random changes in an organism's DNA sequence. They are the ultimate source of new genetic variation (new alleles) in a population. While most are neutral or harmful, beneficial mutations can be acted upon by other evolutionary forces, leading to changes in the gene pool.

What is non-random mating and how does it lead to changes in a population’s gene pool over time?

Occurs when individuals do not mate randomly but choose mates based on certain phenotypic or genotypic traits (e.g., assortative mating, inbreeding). While it changes genotype frequencies, it does not directly change allele frequencies on its own. However, by altering genotype proportions, it can affect the rate at which natural selection or genetic drift can act on certain alleles, indirectly influencing the gene pool's evolution.

What is Hardy-Weinberg Equilibrium and why is it useful when discussing evolution?

Describes a state where allele and genotype frequencies in a population remain constant across generations in the absence of evolutionary influences (no gene flow, mutation, genetic drift, natural selection, or non-random mating). It serves as a null hypothesis against which to test whether a population is evolving; if a population deviates, it indicates that evolution is occurring.

Does evolution have a purpose or direction? Can it produce a perfect organism?

No, evolution does not have a purpose, direction, or goal. It is an ongoing process driven by environmental pressures and random events, not a linear progression towards 'perfection.' It cannot produce a 'perfect' organism because perfection is subjective, environments are constantly changing, and organisms are constrained by their evolutionary history and physiological trade-offs.

What is Hardy-Weinberg equilibrium?

Describes a state where allele and genotype frequencies in a population remain constant across generations. This occurs in the absence of evolutionary influences like gene flow, mutation, genetic drift, natural selection, or non-random mating.

Why is Hardy-Weinberg equilibrium useful when discussing evolution?

It serves as a null hypothesis to test if a population is evolving. If a population's frequencies deviate from Hardy-Weinberg, it indicates that evolution is occurring.

What are the equations associated with Hardy-Weinberg equilibrium and what do their parts relate to?

The allele frequency equation is p + q = 1, p is the dominant allele frequency. q is the recessive allele frequency.

The genotype frequency equation is p^2 + 2pq + q^2 = 1,

p^2 is homozygous dominant, 2pq is heterozygous, and q^2 is homozygous recessive.

How do you solve problems using the Hardy-Weinberg equations?

Start by determining q^2 from phenotypic data, then calculate q by taking the square root of q^2. Once q is known, find p using p = 1 - q, and then compute p^2 and 2pq to find the frequencies of other genotypes.