How does evolution occur? (5 mechanisms)
1) Genetic Drift
2) Mutation
3) Heritable Epigenetic Modification
4) Migration
5) Natural Selection
- -basically anything that changes allele frequencies in population or heritable expression of alleles
Evolution (defn)
The change in allele frequencies in a population across generations.
Genetic drift
totally random changes in allele frequency from generation to generation due to chance (sampling error)
mutation
changes in the genetic code such as errors in DNA replication, gene deletions or duplications, etc.
epigenetic inheritance
heritable changes that are not due to changes in DNA sequence, such as DNA methylation and histone modifications, etc..
migration
alleles moving from one population to another
natural selection
when some alleles favored over others due to an increase in fitness (not random) acts on genetic variation within the population
HIV
- Retrovirus with 2 single strand RNA genomes
- Uses enzyme reverse transcriptase to replicate RNA–>DNA
- Infects macrophages and helper T cells
random fixation (of alleles) (genetic drift)
When an allele frequency becomes 100%, the other alleles are lost by chance
Inbreeding depression (genetic drift)
mating between relatives
outbreeding depression (genetic drift)
mating between completely different species
hybrid vigor (genetic drift)
mating halfway
- optimal state w/ heterozygous offspring
Hardy Weinberg Theorem
States:
- In a non-evolving population, the frequencies of alleles and genotypes in a population remains constant from generation to generation.
- When given allele frequencies, genotype frequencies should be the Hardy-Weinberg expectations.
gene
- a region of genome sequence (DNA or RNA)
locus
location within a genome (can be in a gene)
allele
variant forms of a gene
There are ____ alleles at a locus
2
The frequency of all alleles in a population will add up to ____.
1
The 5 Conditions for Non-evolvingPopulations
1) No mutations
2) Random mating
3) No natural selection
4) Extremely large population size
5) No gene flow
point mutations
single nucleotide substitutions, insertions , or deletions
- Due to DNA replication error in mitosis or meiosis
Gene-level mutations
- Gene insertions (Gene duplications, transposons, horizontal gene transfer)
- Gene deletions (pseudogenoization, transposons)
- Exon shuffling
Chromosome-level mutations
- Chromosome duplications
- Deletions
- Inversions
- Fusions
Genome-level Mutations
- Autopolyploidization
- Allopolyploidization
Horizontal gene transfer
- Transfer of genetic material to another organism that is not its offspring.
- How bacteria evolve.
- Responsible for drug resistance.
