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Biology- Chapter 17- Evolution and Population

Terms in this set (54)

How is genetic variation in organisms studied?
At a level of a population not the individual.
Population
Group of individuals of the same species that live in the same area
Gene Pool
All of the genes that are present in a population;members of a population of species interbreed, there fore they share a common group of genes
Relative (Allelic) Frequency of an allele
Number of times that the allele occurs in a gene pool compared to the number of time other alleles for the same gene occur
Gene Shuffling
Happens during meiosis
Crossing Over
Happens during Prophase 1
How do new alleles arise?
Random mutations, gene shuffling, crossing over, and sexual reproduction
Evolution
Any change in the relative frequency of alleles in a population
If the frequency of the allele changes then
The population is evolving
Inheritable variation can be expressed by
-Single gene trait (freckles) or by polygenic (like eye color in humans)
How many genes control the trait?
The number of phenotypes produced for a given trait
Most phenotypes in generations form a
-Bell-shaped curve
Bell Shaped Curve
The most common variety is represented in the middle of the curve and more extreme variations are on either end of the curve
Evolution shifts the curve by
Changing the percentage of each variation
Directional Selection
Individuals on one end of the curve are better adapted to their environment
Stabilizing Selection
When the average individual is best, the population stabilizes-reduces the percentage of organisms on the extremes
Disruptive Selection
Occurs when either extreme is better adapted for survival than the average
Genetic Drift
Random changes in allelic frequency in small populations; percentages of alleles change more quickly
If populations get separated and each new population only has two of the four variations
-Founder Effect
Bottleneck Effect
Change in allelic frequency after a dramatic reduction in the size of a population
Are populations always evolving?
No, but there are 5 conditions which must be met for a population not to be evolving.
Five Conditions that can disturb genetic equilibrium and cause evolution to occur:
Random mating, large population, no movement into or out of population, no mutations, and no natural selection
Hardy-Weinberg Principle
Allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change
Behavioral Isolation
Occurs when two populations are capable of interbreeding, but do not (due to difference in rituals/ behaviors)
Geographic Isolation
Occurs when two populations cannot reach each other to mate due to a physical barrier
Temporal Isolation
Occurs when the species reproduce at different times of the year
Natural selection works on an organism's?
Phenotype rather than its genotype
Mutation
Any change in the genetic material of a cell
When mutations affect evolution?
By occurring the germ line cells that produce eggs or sperms and if they change in the phenotype that affects the fitness
How does sexual reproduction affect a population's genetic variation?
By genetic recombination during sexual reproduction that can produce many different phenotypes with new genetic combinations
Identify two ways in which genes can be recombined during meiosis
Independent assortment and crossing over
What is lateral gene transfer?
Passing of genes from one organism to another organism that is not its offspring
How does lateral gene transfer affect variation?
Occurs between organisms of the same species or organisms of different species. It increases genetic variation in any specie that picks up the "new" genes.
Height in humans are an example of what kind of trait?
-Polygenetic
Each gene of a polygenic trait often has two or more ______.
Alleles
If a trait made an organism less likely to survive and reproduce, what would happen to the allele for that trait?
Fewer copies of the allele will pass for future generations and the allele could disappear from the gene pool completely
If a trait had no effect on an organism's fitness, what would likely happen to the allele for that trait?
The allele wouldn't be under pressure from natural selection and its frequency would almost stay the same
What effect does stabilizing selection have on variation in a population?
It would decrease the variation a population
Directional Graph
Individuals at one end of the curve have higher fitness than individuals in the middle or at the end
Stabilizing Graph
Individuals near the center of the curve have higher fitness than individuals at either end
Disruptive Graph
Individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle
Genetic Equilibrium
Allele frequencies in its gene pool don't change
Speciation
Formation of new species
What does it mean for two species to be reproductively isolated from each other?
It means they no longer interbreed and the gene pool splits
What must happen in order for a new species to evolve?
Populations must be reproductively isolated from each other
What is an example of temporal isolation?
Two or more species reproduce at different times
Single-Gene Trait
A trait controlled by a single gene
Polygenic Traits
Controlled by two or more genes
For most genes, a gene pool typically contains how many alleles?
Two or more alleles
What occurs when allele frequencies change as a result of the migration of a small subgroup of a population?
-Founder effect
What is one requirement to maintain genetic equilibrium?
No mutations
What situation occurs when members of two different species cannot interbreed and produce fertile offspring?
-Reproductive isolation
Reproductive Isolation
Members of two populations do not interbreed and produce fertile offspring
Which form of evidence for evolution allows scientists to determine the amount of time that has passed since to species diverged from a common ancestor?
-Molecular Clock
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