Bio Exam 2 Flashcards
Natural Selection
The process by which individuals with certain heritable traits tend to produce more surviving offspring than do individuals without those traits, often leading to a change in the genetic makeup of the population. A major mechanism of evolution. The only evolutionary process that produces adaptation.
Genetic Drift
Any change in allele frequencies due to chance. Causes allele frequencies to drift up and down randomly over time, and eventually can lead to the fixation or loss of alleles.
Gene flow
The movement of alleles between populations; occurs when individuals leave one population, join another, and breed.
Mutation
Any permanent change in the hereditary material of an organism (DNA in most organisms, RNA in some viruses). The only source of new alleles in populations.
Hardy-Weinberg Principle
A principle of population genetics stating that genotype frequencies in a large population do not change from generation to generation in the absence of evolutionary processes (e.g., mutation, gene flow, genetic drift, and selection), and nonrandom mating.
Gene pool
All the alleles of all the genes in a certain population.
Inbreeding Depression
The decline in average fitness that takes place when homozygosity increases and heterozygosity decreases in a population due to inbreeding; results from the exposure of deleterious recessive alleles to selection
Directional selection
A mode of natural selection that favors one extreme phenotype with the result that the average phenotype of a population changes in one direction. Generally reduces overall genetic variation in a population. Compare with disruptive selection and stabilizing selection.
Stabilizing selection
A mode of natural selection that favors phenotypes near the middle of the range of phenotypic variation. Reduces overall genetic variation in a population. Compare with disruptive selection and directional selection.
Disruptive selection
A mode of natural selection that favors extreme phenotypes at both ends of the range of phenotypic variation. Increases overall genetic variation in a population. Compare with stabilizing selection and directional selection.
Balancing Selection
A mode of natural selection in which no single allele is favored over time and across locations, on average. An overall balance of fitness and frequency is maintained among alleles.
Founder effect
A change in allele frequencies that often occurs when a new population is established from a small group of individuals (founder event) due to sampling error (that is, the small group is not a representative sample of the source population).
Genetic bottleneck
A reduction in the diversity of alleles in a population resulting from a sudden decrease in the size of that population (population bottleneck) due to a random event
Hardy-Weinberg Equilibrium
Allele frequencies will not change if there is:
1. No mutation
2. No gene flow (no immigration/emigration)
3. No genetic drift (large population size)
4. No natural selection
5. Random mating
Gene pool equation
p + q = 1
Offspring genotype equation
p^2 + 2pq + q^2 = 1
Offspring allele equation
fr(A) = p^2 + pq
fr(a) = q^2 +pq
H-W formula
- Genotype frequencies
- Calculate observed alleles frequencies fr(A) = p + ½(pq) and fr(a) = q +½(pq)
- Calculate expected genotype frequencies f(AA)= p^2 from p value above, f(Aa)=2pq, f(aa)= q^2
- Compare observed vs. Expected –> if supports H-W no evolution
Genetic Isolation
Something causes a population to separate – remove gene flow
Allopatric Speciation
live in different areas
Sympatric Speciation
live in different areas
Genetic divergence
Mechanisms of change lead to
genetic and phenotypic differences.
Biological Species concept
The definition of a species as a population or group of populations that are reproductively isolated from other groups. Members of a species have the potential to interbreed in nature to produce viable, fertile offspring but cannot interbreed successfully with members of other species.
Morphological Species concept
The definition of a species as a population or group of populations that have measurably different anatomical features from other groups.
Phylogenetic Species concept
The definition of a species as the smallest monophyletic group in a phylogenetic tree.
Hybridization
Mix between two things
Clade/lineage
An evolutionary unit that includes an ancestral population and all of its descendants but no others
Phylogenetic tree
A branching diagram that depicts the evolutionary relationships among species or other taxa
Nodes
In a phylogenetic tree, the point where two branches diverge, representing the point in time when an ancestral group split into two or more descendant groups; also called fork.
Outgroup
Any taxon that is not part of the taxonomic group being studied; researchers often select one or more outgroups that are closely related to the ingroup to help root phylogenetic trees and to determine the direction of character changes
Ancestral Trait
A trait found in the ancestors of a particular group.
Derived Trait
A trait that is a modified form of an ancestral trait, found in a descendant
Monophyletic Group
An evolutionary unit that includes an ancestral population and all of its descendants but no others. Also called a clade or lineage
Homology
Similarity among organisms of different species due to shared ancestry. Features that exhibit such similarity (e.g., DNA sequences, proteins, body parts) are said to be homologous.
Homoplasy
Similarity among organisms of different species due to reasons other than common ancestry, such as convergent evolution
Synamorphies
A shared, derived trait found in two or more taxa that is present in their most recent common ancestor but is missing in more distant ancestors. Useful for inferring evolutionary relationships
Parsimony
The principle that the most likely explanation of a phenomenon is the most economical or simplest. When applied to comparison of alternative phylogenetic trees, it suggests that the one requiring the fewest character changes is most likely.
Convergent Evolution
The independent evolution of similar traits in different species due to adaptation to similar environmental conditions and a similar way of life.
Cuticle
A protective coating secreted by the outermost layer of cells of an animal or a plant; often functions to reduce evaporative water loss.
Stomata
Generally, a pore or opening. In plants, a microscopic pore on the surface of a leaf or stem through which gas exchange occurs; typically surrounded by specialized cells that open the pore.
Vascular tissue
In plants, tissue that transports water, nutrients, and sugars. Made up of the complex tissues xylem and phloem, each of which contains several cell types
Embryophyte
A plant that nourishes its embryos inside its own body. All land plants are embryophytes.
Gametangia
(1) The gamete-forming structure found in all land plants except angiosperms. Contains a sperm-producing antheridium and an egg-producing archegonium. (2) The gamete-forming structure of some chytrid fungi.
Spores
In eukaryotes, a single haploid cell produced by meiosis; it is distinct from a gamete, however, in being able to grow into a multicellular, haploid organism through mitotic divisions directly (no fertilization required).
Pollen
a fine powdery substance, typically yellow, consisting of microscopic grains discharged from the male part of a flower or from a male cone. Each grain contains a male gamete that can fertilize the female ovule, to which pollen is transported by the wind, insects, or other animals.
Seeds
A plant reproductive structure consisting of an embryo, associated nutritive tissue (endosperm), and an outer protective layer (seed coat). In angiosperms, develops from the fertilized ovule of a flower
Flowers
seed-bearing part of a plant, consisting of reproductive organs (stamens and carpels) that are typically surrounded by a brightly colored corolla (petals) and a green calyx (sepals)
Fruit
In flowering plants (angiosperms), a mature, ripened plant ovary (or group of ovaries), along with the seeds it contains and any adjacent fused parts; often functions in seed dispersal. See aggregate fruit, multiple fruit, and simple fruit.
Green Algae
A paraphyletic group of photosynthetic organisms that contain chloroplasts similar to those in land plants. Often classified as protists, green algae are the closest living relatives of land plants and form a monophyletic group with them
Non-Vascular plants
Non-vascular plants are plants without a vascular system consisting of xylem and phloem. Instead, they may possess simpler tissues that have specialized functions for the internal transport of water.
Seedless vascular plants
Seedless vascular plants are ancient land plants that have tubes to transport water and nutrients, but no seeds or flowers to reproduce (rely on spores)
Gymnosperms
A vascular plant that makes seeds but does not produce flowers. The gymnosperms include five lineages of green plants (cycads, ginkgoes, redwoods, pines, and gnetophytes). Compare with angiosperm.
Angiosperms
A flowering vascular plant that produces seeds within mature ovaries (fruits). The angiosperms form a single lineage
