Lecture 19 Flashcards
In population genetics,evolutionis defined as ?
a change in the frequency ofallelesin a population over time.
Population?
all the individuals of 1 species living in a specific area, that have the potential to breed
Individual: Genotype
Population: __?
Gene pool
Gene pool?
All the alleles present in a population
Micro-Evolution: change in __
gene pool
MICROEVOLVED: SAME SPECIES
Microevolution
Selective pressures act on individuals
BUT
Changes (evolution) seen in a POPULATION over TIME: see changes in the frequency of certain (not all) alleles ie changes in the gene pool
Same species, just change in allele frequency in gene pool
Hardy-Weinberg Principle used to see if a population is micro-evolving?
For a population that is not evolving ie is at genetic equilibrium:
the frequencies of alleles and genotypes in a population’s gene pool remain constant from generation to generation
Hardy-Weinberg Principle?
A sexually reproducing population will be at genetic equilibrium (not evolving) if all 5 conditions to genetic equilibrium are met
natural selection not occurring mating is random no net mutations large population (avoid genetic drift) no migration between populations
If any of these are NOT met, evolution can occur
Note: even if only 1 gene out of the thousands is evolving, then that population is said to be evolving
the frequencies of what is observed for a microevolution? (Genotypes, Alleles, Phenotypes)
only genotypes and alleles. If constant
NO Evolution occurring
Why isn’t phenotype observed in the microevolution?
Because Aa and AA give the same phenotype (complete dominance), no change in phenotype. Phenotypes can be effected by the environment as well.
Hardy-Weinberg Principle null and alternative hypothesis?
Null hypothesis: the population is in Hardy–Weinberg proportions (the population is not evolving).
Alternative hypothesis: the population is not in Hardy–Weinberg proportions (the population is micro-evolving).
what p value is acceptable?
less than 0.05
Fitness (in evolution)
includes its ability to survive, find a mate, produce offspring—& ultimately leave its genes in the next generation.
Natural selection relies on __, __ & __
survival, mate-finding & reproduction
Natural selection causes changes in allele frequencies leading to __
adaptive evolutionary change
3 modes of selection of phenotypes
- Stabilizing: favors intermediate variants.
- Directional: favors one phenotypic extreme
- Disruptive: favors individuals at both extremes of the phenotypic range. Ex birds with big beaks eat big seeds, little beaks small holes in trees, birds with medium beaks die out
Sexual selection
non-random mating that is an example of natural selection
Can result in stabilizing selection, directional selection, or disruptive selection
Non-adaptive factors leading to evolution
- Non-random mating that’s not adaptive
- Genetic mutations
- Genetic drift: Bottleneck, founder effect
- Gene flow
Non-adaptive factors leading to evolution:
1) Non-random mating that’s not adaptive
Inbreeding, which occurs when individuals with similar genotypes are more likely to mate with each other rather than with individuals with different genotypes.
inbreeding can lead to a reduction in genetic variation in the population
frequencies of random mating b/w AA, Aa, aa individuals
The combined genotype frequencies of the offspring for the 6 crosses above will be AA 25%, Aa 50%, aa 25%
Non-adaptive factors leading to evolution:
2) Genetic mutations
- Genetic mutations are random
- Most mutations occur in somatic cells & are therefore lost with the death of the individual
- Only mutations in gametes can be passed on to offspring
- Mutation rates low in animals & plants
- Microorganisms: more generations/time period, so accumulate mutations faster
Point mutation vs Chromosomal mutation
Point mutation = one nucleotide base change: Rarely increases reproductive success
Chromosomal mutation: deletion, duplication: Usually harmful
__ and __ produce the variation that makes evolution possible
Mutation & sexual recombination
Mutations in DNA sequence rare in plants & animals, important for asexually-reproducing organisms
Sexual recombination much more important
Non-adaptive factors leading to evolution:
3) Genetic drift
Occurs when changes in allele frequencies from 1 generation to another occur because of random events that occur in small populations
- Bottleneck
- Founder effect
Both cause a reduction in the genetic variation of the population
Bottleneck?
A sudden decrease in population size caused by adverse environmental factors
Resulting in a reduction in genetic diversity
Founder effect
Individuals leave the original population & start a new population(s). New population (founders) has less genetic variation than original (parent) population
Small populations are __ susceptible to genetic drift
more
Allele frequencies more likely to change by random fluctuations (genetic drift) than in a large population.
Example: in a population of only a few individuals, an allele at low frequency could be completely lost by chance.
Factors leading to evolution:
4) Gene Flow
- Transfer of alleles b/w populations, of same species
- Populations: recipient pop. gains alleles donor pop. may lose alleles
- Results from the movement of fertile individuals or gametes: alleles move too
Usually ↑ genetic variation in recipient population
Horizontal gene transfer
Movement of genetic material between different species
Selective pressures leading to evolution: (Darwin) Natural selection:
(Darwin) Natural selection: Environment must change to select new phenotype or organism migrates to a different environment
Selective pressures leading to evolution: (Beyond Darwin) Other selective pressures:
(Beyond Darwin) Other selective pressures: These are not adaptive: genetic drift, gene flow between populations of the same species, horizontal gene flow
why sexual selection is considered to be an example of natural selection
Natural selection (adaptive: adapting to the environment) Includes sexual selection (adaptive non-random mating)
