Chapter 17 Flashcards
Microevolution
Looking at changes in the genetic make-up (the genotype) of populations of a species over time.
Quantitative Variation
Variation that is measured on a continuum (such as height in human beings) rather than in discrete units or categories.
Qualitative variation
Variation that exists in two or more discrete states, with intermediate forms often being absent.
Polymorphism
The existence of discrete variants of a character among individuals in a population.
How do we know whether phenotypic variation is caused by environmental or genetic differences?
We test for environmental factors by changing one environmental variable and measuring the effects. Breeding experimentation can demonstrate the genetic basis of phenotypic variation.
Population Genetics
Focus on the genetic variation that exists within a population and how this changes over time as a result of evolution. It first describes the genetic structure of a population, then they create and test hypotheses.
Allele
One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.
Haploid vs Diploid Organism
Haploid organisms have only one possible allele of a gene because there is only one copy of each gene. Diploid organisms possess two alleles for each gene; these may be the same alleles or different.
Locus
The location of a gene on a chromosome
Evolution
The main unifying concept in biology, explaining how the diversity of life on Earth arose and how species change over time in response to changes in their abiotic environment. The change in allele frequencies from one generation to the next.
Gene Pool
The sum of all alleles at all gene loci in all individuals in a population.
Hardy-Weinberg Principle
An evolutionary rule of thumb that specifies the conditions under which a population of diploid organisms achieve genetic equilibrium. A mathematical model that specifies the conditions that are necessary so that allele and genotype frequencies do not change from one generation to the next. p^2+2pq+q^2=1
Genetic Equilibrium
The point at which neither the allele frequencies nor the genotype frequencies in a population change in succeeding generations. Only possible if these conditions are met:
1. The population is closed to migration from other populations.
2. The population is infinite in size.
3. No mutation is occurring in the population.
4. All genotypes in the population survive and reproduce equally well.
5. Individuals in the population mate randomly with respect to genotype.
Gene Flow
The transfer of genes from one population to another through the movement of individuals or their gametes. Violates the Hardy-Weinberg requirements.
Genetic Drift
Random fluctuations in allele frequencies as a result of chance events; usually reduces genetic variation in a population.
Founder Effect
An evolutionary phenomenon in which a population that was established by just a few colonizing individuals has only a fraction of the genetic diversity seen in the population from which it was derived.
Population Bottlenecks
Factors such as disease, starvation, and hunting may kill a large proportion of the individuals in a population. The large reduction in population size is associated with a decrease in the size of the gene pool and, therefore, the genetic diversity of the population. Alleles can be totally lost.
Point Mutation
A single nucleotide (base) is changed. This is also referred to as substitution
Deletion
One or more nucleotide base pairs are removed from a DNA sequence
Insertion
One or more nucleotide base pairs are introduced into a DNA sequence
Inversion
A segment of DNA breaks and is inserted back into its original position in the reverse orientation
Duplication
DNA is copied twice. The duplication can be part of a gene, a whole gene, or an entire genome.
Mutation
A change to the double-strand sequence of DNA. Common factors that cause mutation include radiation, and some hazardous chemicals. However, it may occur during normal cellular processes. This includes errors in copying DNA during DNA replication as well as movement of transposable elements.
Four key aspects of Mutation
First, mutations can occur in the genomes of any cell, but for mutations to alter allele frequencies within a population, the mutation must occur in the DNA of cells that go on to produce gametes. Second, mutations are random and spontaneous events, meaning the location is unpredictable. Third, mutations are not directed to occur at specific genes because of the selective pressures on a population. Fourth, mutation does not tend to result in increased fitness. In fact, most mutations either have no effect on fitness or they will be harmful.
Directional Selection
A type of selection in which individuals near one end of the phenotypic spectrum have the highest relative fitness. Shift a trait away from the existing mean and toward a favoured extreme.
Stabilizing Selection
When individuals expressing intermediate phenotypes have the highest relative fitness. Eliminating phenotypic extremes, stabilizing selection reduces genetic and phenotypic variation, and increases the frequency of intermediate phenotypes. Most common type of natural selection.
Disruptive Selection
When extreme phenotypes have higher relative fitness than intermediate phenotypes. Thus, alleles producing extreme phenotypes become more common. Under natural conditions, disruptive selection is much less common than directional and stabilizing selection.
Non-random Mating
Many organisms select mates based on specific phenotypes and thus, often a particular underlying genotype.
Inbreeding
Mating between related individuals resulting in an increase in the proportion of both homozygous genotypes and decrease in heterozygotes.
Inbreeding Depression
Decline of average fitness of inbred individuals in a population. The explanation for this is that deleterious alleles tend to be recessive, and yet they perpetuate in a typical population because they are carried in heterozygotes where they are effectively masked. However, in inbreeding there is an increase of homozygous recessive genotype at any particular locus that are usually harmful and even lethal to individuals that carry them.
Sexual Selection
A form of natural selection established by male competition for access to females and by the females’ choice of mates. Favours those with specific traits that enhance their ability to mate. Often the cause of sexual dimorphism
Balancing Selection
A type of natural selection in which more than one allele is actively maintained in a population. Natural selection preserves balanced selection when (1) heterozygotes have higher relative fitness, (2) when different alleles are favoured in different environments, and (3) when the rarity of a phenotype provides a selective advantage.
Heterozygote Advantage
When heterozygotes have higher relative fitness than either homozygote.
Frequency-Dependent Selection
Sometimes genetic variability is maintained in a population because rare phenotypes have higher relative fitness than more common phenotypes.
