| A | B |
|---|
| Mutation | a change in the structure of a DNA molecule. - occurs primarily during DNA replication (copying errors |
| DNA repair enzymes (DNA polymerases) | can recognize copying errors, cut out base-pair mismatches, and put in the correct sequence. |
| Point mutations (gene mutations | involve the deletion, addition, or substitution of a single nucleotide base pair into a gene. |
| Substitution | involves replacing one nucleotide base with a second one. |
| Deletion | involves the loss of a base pair from a gene. |
| insertion | nvolves the addition of a base pair to a gene |
| deletions and insertions | strongly disrupt protein function (cause frameshift mutations). |
| point mutations may be: | beneficial (rare) deleterious (common) neutral (common; due to redundancy of genetic code) |
| Mutator genes | have been identified that control mutation rates of other genes. |
| Chromosomal mutations | mechanisms. change the structure of entire chromosomes (most are lethal or detrimental). |
| chromosomal Deletion | an entire segment of the chromosome breaks off and is lost. |
| Crossing over (genetic recombination) | - is a beneficial chromosomal mutation. - generates novel genetic variation in offspring that selection can operate on. |
| regulatory genes | control the expression of other genes during development. |
| minor mutations | slight change in phenotype |
| Homeotic genes | - affect the position of structures on the body. |
| macromutations | Mutations alter where body parts form |
| Biological Species Concept | Ernst Mayr, If two geographically isolated populations were brought together, would they interbreed? |
| examples where BSC is difficult to apply | (1) Asexually reproducing organisms: (2) Extinct species: cannot test for reproductive isolation in fossils. (3) allopatric populations-geographically isolated pop. |
| paropatric | side by side populations that touch |
| sympatric | populations that overlap |
| Evolutionary species concept (ESC) | a species is a lineage evolving separately from other lineages and having its own unitary evolutionary role and tendencies. |
| Major Problem: ESC | requires a subjective guess as to whether groups are on separate pathways. |
| major benefit ESC | is useful for dealing with fossil specimens and asexually-reproducing organisms |
| Reproductive Isolating Mechanisms | RIMs are mechanisms that prevent closely related species from interbreeding.times of the day or year. |
| two categories of RIM's | Premating (prezygotic) RIM’s - prevent gamete wastage Postmating (postzygotic) RIM’s - result in gamete wastage |
| Temporal isolation | where species breed at different times of the day or year. |
| Ecological isolation | where syntopic species use different habitats during the breeding season. |
| Behavioral isolation (ethological isolation) | one species is not responsive to courtship by a second. |
| Mechanical isolation | where shape or size of reproductive structures are incompatible. |
| Gametic isolation | where union of gametes is mediated by chemical signals. |
| Genetic incompatibility | sperm and egg are inviable or embryo dies because of genetic mismatch. |
| Hybrid sterility | hybrids are often vigorous but sterile (reduced output of offspring) |
| Complete sterility | no offspring produced. |
| Partial sterility | fewer than normal number produced. |
| Speciation | is essential for maintaining biodiversity since extinctions are always occurring. |
| anagenesis | single lineage |
| cladogenesis | branching lineage |
| Geographic (Allopatric) Speciation | appears to be the primary way in which new species originate. |
| steps of geographic speciation | (1) Subsets of populations become geographically isolated from one another. (2) The geographic isolates undergo genetic and phenotypic differentiation (racial differentiation). (3) divergence continues until geographic isolates develop reproductive isolating mechanisms (or meet other species criteria). |
