How can we help?

You can also find more resources in our Help Center.

34 terms

Exam Review - Population Genetics

STUDY
PLAY
Gene Pool
consists of all genes, including all the different alleles, that are present in a population
Relative Frequency
the number of times that the allele occurs in a gene pool compared with the number of times other alleles for the same gene occur
Single-Gene Trait
a trait controlled by a single gene that has two alleles
Polygenic Trait
trait that is controlled by more than one gene which results in large variation of phenotypes, ie. height, weight, hair color, skin color
Directional Selection
form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve
Stabilizing Selection
form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end
Disruptive Selection
form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle
Genetic Drift
changes in the gene pool of a small population due to chance; tends to reduce genetic variation.
Founder Effect
a situation in which allele frequencies change as a result of the migration of a small subgroup of a population
Hardy-Wienberg Principle
allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change
Genetic Equilibrium
a population in which the frequency of alleles remains the same over generations
Speciation
the formation of new species as a result of evolution
Reproductive Isolation
separation of species or populations so that they cannot interbreed and produce fertile offspring
Behavior Isolation
occurs when two animals become isolated from each other because of some change in behavior by one member or group; example: different mating/courtship behavior
Geographic Isolation
form of reproductive isolation in which two populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water
Temporal Isolation
form of reproductive isolation in which two populations reproduce at different times
In terms of genetics, what is evolution?
a change in the allele frequency within a population over many generations
Name the two sources of genetic variation.
genetic shuffling and mutations during gamete formation
Which type of genetic variation is responsible for the most variation within a population?
genetic shuffling
Compare single-gene trait and polygenic trait.
Single-gene trait: inheritance of a trait controlled by one gene; results in little variation within the phenotypes (ex. widow's peak)
Polygenic trait: inheritance of a trait controlled by 2 or more genes; results in a large variation within the phenotypes (ex. human height)
What does the number of phenotypes in a population depend on?
The number of genes that control a trait; the more genes that control a trait the more variation within a population
Look at the picture to the right. The top row is brown lizards. The middle row is red lizards. The bottom row is black lizards. What evidence is there that evolution is occurring?
Evidence that evolution is occurring is the change in allele frequencies over many generations; the allele frequency for brown lizard is decreasing; the allele frequency for black lizards is increasing and the allele frequency for red lizards disappears
How do differences in fitness affect relative frequency of alleles? Use the picture of lizard populations to answer this question.
The brown and red lizards have a reduced fitness thus their numbers are decreasing; the black lizards have an increased fitness thus their numbers are increasing. Thus, there must be some advantage to having a black color and some disadvantage for having brown and red color.
Name the three ways that natural selection can affect the distribution of phenotypes of a population for polygenic traits.
Directional, stabilizing and disruptive selection
Disruptive Selection
occurs when individuals at both ends of a distribution curve have higher fitness than individuals in the middle of the curve
Stabilizing Selection
occurs when individuals in the middles of a distribution curve have higher fitness than individuals at either end of the curve
Directional Selection
occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or the other end of the curve
What causes genetic drift?
In small populations, individuals that carry a particular allele may leave more descendants than other individuals do, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population
How is founder effect related to genetic drift?
allele frequencies change as a result of the migration of a small subgroup of a population; One example of the founder effect is the evolution of several hundred species of fruit flies found on different Hawaiian Islands. All of those species descended from the same original mainland population. Those species in different habitats on different islands now have allele frequencies that are different from those of the original species
What is genetic equilibrium?
situation in which allele frequencies remain constant
Why can we say genetic equilibrium the opposite of evolution?
Evolution is a change in allele frequencies within a population while genetic equilibrium is when allele frequencies stay constant (do not change) within a population.
What five conditions must be met for a population to be at genetic equilibrium?
Hardy Weinberg Principle: Five conditions are required to maintain genetic equilibrium from generation to generation: (1) There must be random mating; (2) the population must be very large; and (3) there can be no movement into or out of the population, (4) no mutations, and (5) no natural selection.
Speciation is the formation of a new species because of reproductive isolation. What is reproductive isolation?
When the members of two populations cannot interbreed and produce fertile offspring
Name and describe three ways that species can become reproductively isolated.
Temporal isolation, Behavioral isolation and geographic isolation can all lead to reproductive isolation.
Temporal isolation: species reproduce at different times
Behavioral Isolation: when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior
Geographic isolation: two populations are separated by geographic barriers such as rivers, mountains, or bodies of water