Download mechanisms of evolution presentation

Answer in writing: what is DNA? Where is yours?
A very long macromolecules that contains your genetic
material. It’s found in the nucleus of each one of your
cells.
Answer in writing: what is a gene?
A segment of DNA which codes for a protein, which
determines a trait.
Evolution: a change in gene frequencies in
a population between generations
4 Mechanisms of Evolution
1)
2)
3)
4)
Gene flow (migration)
Genetic drift (population bottlenecks)
Mutation
Natural selection
Mechanisms of Evolution 1: Gene Flow (Migration)
The exchange of genes between populations
• decreases variation in population emigrated from
• increases variation in population immigrated to
• a significant force in human evolutionary history
(no speciation)
• accelerated travel/gene flow in recent years
What was an example of gene flow in “the island of the
colorblind?” Look at your video sheet and write “gene
flow” next to it.
Mechanisms of Evolution 2:
Genetic Drift
• occurs with isolation (absence of gene
flow) and/or small population size
• founder effect (e.g. first settlers on an
island)
Polydactyly (Ellis-van Creveld
syndrome)
• genetic bottlenecks (e.g. depopulation
from catastrophe)
What was an example of genetic drift in “the island of
the colorblind?” Look at your video sheet and write
“gene flow” next to it.
“The Island of the Colorblind” as an example of
(three) forces of evolution:
• a bounded population
• a mutation: achromatopsia gene
• arrival of a European achromatopsia gene in the 18th century:
gene flow (migration)
• isolation: genetic drift
• the typhoon: genetic drift (population bottleneck)
• religious practices (encouraged inbreeding): genetic drift
Forces of Evolution 3: Mutation
Mutation is the source of new genetic variation:
• actual change in a portion of the DNA of an organism.
• some harmful, some beneficial, most have no effect and
are passed unnoticed to offspring.
• most common type of mutation is caused by copying errors
during meiosis (sex cell division)
• mutations do not cause evolution, they provide the material
upon which the other evolutionary mechanisms act. Only
way to introduce genetic variation from within a population.
• Example: sickle cell anemia: mutation of recessive
hemoglobin gene. Misshapen red blood cells cannot
transport oxygen to tissues.
Sickle-cell
hemoglobin
HbS HbS
1. Hemoglobin molecule
Normal
hemoglobin
HbA HbA
valine
2. Hemoglobin beta chain
3. Red blood cells
Forces of Evolution 4: Natural Selection
• mutation on its own has little effect on changing allele frequencies
• but mutation + natural selection = rapid evolutionary change
• sickle-cell carriers are protected from malaria
Distribution of malaria
Distribution of sickle-cell anemia
Forces of Evolution 4: Natural Selection
• sickle-cell carriers are protected from malaria
•What is evolution? - a change in genes frequency in a
population between generations
- sickle-cell genes decline in frequency when malaria
is not present
- ex: decrease sickle-cell genes in African American
population
Forces of Evolution 4: Natural Selection
• Natural selection: some individuals have genes that allow them to
survive and reproduce more than other individuals.
• These individuals have higher fitness (more offspring), and by
producing more offspring, will pass on more genes to the next
generation.
• This increases the frequency of their genes in the population =
natural selection!
•Natural selection acts on the individual, although the population
evolves.