Biology "Five Agents of Evolutionary Change"

1. Five Agents of
Evolutionary Change
Prepared by: John Rey D. Ravago
BSED SCIENCE 1-A
20.3

2. Learning Outcome
1)Define the five processes that can cause evolutionary change.

3. • The five assumptions of the Hardy–Weinberg principle also indicate
the five agents that can lead to evolutionary change in populations.
They are mutation, gene flow, nonrandom mating, genetic drift in small
populations, and the pressures of natural selection. Any one of these
may bring about changes in allele or genotype proportions.

4. Five Agents that Can Lead to Evolutionary
Change in Populations
Mutation Changes Alleles.
Mutations are the ultimate source of genetic variation.
Because mutation rates are low, mutation usually is not
responsible for deviations from Hardy-Weinberg
equilibrium.
The ultimate source of variation. Individual mutation
occur so rarely that mutation alone usually does not
change allele frequency much.

5. Five Agents that Can Lead to Evolutionary
Change in Populations
Gene flow occurs when alleles move between
populations.
Gene flow is the migration of new alleles into a
population. It can introduce genetic variation and can
homogenize allele frequencies between populations.
A very potent agent of change. Individuals or gametes
move from one population to another.

6. Five Agents that Can Lead to Evolutionary
Change in Populations
Nonrandom mating shifts genotype frequencies.
Assortative mating, in which similar individuals tend to
mate, increases homozygosity; disassortative mating
increases the frequency of heterozygotes.
Inbreeding is the most common form. It does not alter
allele frequency but reduces the proportion of
heterozygotes.

7. Five Agents that Can Lead to Evolutionary
Change in Populations
Genetic drift may alter allele frequencies in small
populations.
Genetic drift refers to random shifts in allele frequency. Its
effects may be serve in small populations.
Statistical accidents. The random fluctuation in allele
frequencies increases as population size decreases.

8. Five Agents that Can Lead to Evolutionary
Change in Populations
Selection favors some genotypes over others.
For evolution by natural selection to occur, genetic
variation must result in differential reproductive success,
and it must be inheritable.
The only agent that produces adaptive evolutionary
changes.

9. 5 Assumptions of a Hardy-Weinberg
Population
1) No Selection
2) No Mutation
3) No Gene Flow-No migration between populations to change allele
frequencies
4) Infinite Population is necessary because the larger the population size is,
the harder to change the allele frequency
5) Random Mating which is pretty much what it says: Mating being based on
nothing other than the pure chance, making it random