17. Genes within Populations Hardy-Weinberg Equilibrium Flashcards
Define the five processes that can cause evolutionary change
Mutation.- introduces new alleles
- Gene Flow - equalizes allele frequencies between populations
- Non-random mating -shifts the frequencies
- Genetic drift - causes random fluctuations in allele frequencies in small populations.
- 1. Founder effect
- 2. Bottleneck effect
- Natural Selection favours certain genotypes
- 1. Artificial
- 2. Sexual
- 3. Natural
Define and contrast disruptive, directional and stabilizing selection
Disruptive selection
Selection removes heterozygous types. Fig 20.14 ex. African black-bellied seed cracker have large and small beaks but not intermediate size.
Directional selection
Selection eliminates one extreme from a phenotypic array. Fig 20.15 favours one end of the spectrum only.
Stabilizing selection
Selection acts to eliminate both extremes from an array of phenotypes. ex fig 20.16 birth weight stabilizes between 7 and 8 pounds.
Define evolution and population genetics
Evolution refers to how an entity (social system, a gas, a planet) changes through time. In terms of biological evolution, we tend to think of it as “descent with modification”. Evolution can result from any process that causes a change in the genetic composition of a population. Population genetics is defined as the study of the properties of genes in populations. It studies gene variability through statistical analyses.
Explain how these processes can cause populations to deviate from Hardy-Weinberg equilibrium.
MUTATION: Changes alleles. Ultimate source of genetic variation and makes evolution possible. It changes the proportions of particular alleles in a population
GENE FLOW: Occurs when alleles move between populations. Frequencies will change from generation to generation, which means that the populations will not be in Hardy-Weinberg equilibrium.
NATURAL SELECTION: favors some genotypes over others. Environmental conditions determine which individuals in a population survive and produce the most offspring.
NONRANDOM MATING: Shifts genotype frequencies. Individuals with certain genotypes mate with one another more commonly than would be expected on a random basis. Ex. Assortative mating → phenotypically (and thus genotypically) similar individuals are more likely to produce offspring with 2 copies of the same allele. Increases the proportion of homozygous individuals.
GENETIC DRIFT: May alter allele frequencies in small populations. It can also lead to the loss of alleles in isolated populations. Ex. Bottleneck effect, founder effect
Explain the Hardy-Weinberg principle
“Genotype frequencies in a population remain constant between generations in the absence of disturbance by outside factors”
It means no evolution can occur.
it describes a NON-EVOLVING population
Describe the characteristics of a population that is in Hardy-Weinberg equilibrium
-No mutations
-No gene flow
-No selection
-Random mating
-Large population
Demonstrate how the operation of evolutionary processes can be detected using the Hardy-Weinberg equation
Finding that a population is not in Hardy-Weinberg equilibrium indicates that one or more evolutionary agents are operating.
Define evolutionary fitness
Fitness is defined by an organism’s reproductive success relative to other members of its population. So when we say “survival of the fittest”, we refer to the survival of the individual that produce the greatest number of offspring.
What is the difference between natural selection and evolution?
- Natural selection is a process that leads to evolution
- Evolution is the historical record, or outcome, of change through time
- Evolution is driven by the environment occurring as populations become adapted
