Transcript 4Modern Evolution Regents

Modern Evolution
Miss Hoffman
Charles Darwin
• Darwin could not account for the genetic
reasons for variations that he observed
among organisms
– Therefore theories to how variations occur
were created.
• Mutation Theory
• Modern Theory of Natural Selection
Mutation Theory
• What is a mutation?
– Changes in the genetic information
– Occurs during DNA replication
• Occurs randomly
– Causes variations
• How does this cause variations in
species?
– If a mutation is favorable, and it helps the
organisms survive and reproduce, it is
inherited
Modern Theory of Natural Selection
• What happens if the Environment
changes?
– Genes that previously were neutral or had low
adaptive value may become favorable and
increase in number
Species that are…
• More likely to evolve:
- Reproduce quickly and
often
- reproduce sexually
- genetically varied
- have more mutations
Ex. insects
• Less likely to evolve:
- reproduce asexually
- no genetic variation
- have fewer mutations
Ex. amoeba
Evolution in Our Time
• Spraying of insecticides
– DDT sprayed to kill black flies
– After a few spraying most died
– Some flies had genes that made them resistance to
DDT
– Before DDT these genes were neutral
– After the spraying, only the flies that were resistant
survived
– Since most were killed, little competition
– Resistant genes rapidly increase in number
– DDT was no longer effective
Variations Present
Resistant to Pesticide
Evolution in Our Time
• Antibiotics and Bacteria
– Some bacteria are naturally resistant to
antibiotics
– Therefore they live and pass on the resistant
gene
– Antibiotics no longer work on that bacteria
Evolution in Our Time
• English Peppered Moth
– In Manchester- there existed two colors of peppered
moth (light and dark)
– Before the industrial revolution trees were lighter.
– Light colored moths were more common, because they
blended with the environment (white birch trees)
– Soot and pollution from the industry made the
environment darker
– Light colored moths became visible and were eaten by
birds
– Dark moths could not be seen, so they were able to
reproduce and pass on the dark colored gene
– Population shifted from light to dark
Population of Peppered Moths changed from white (normal) to
dark grey (mutant) over many generations
Prior to Industrial Revolution
After Clean Air Act
After IR
Before Clean Air Act
Environmental changes causes the allelic frequency to change
Human Affect Our Own Evolution
• How can humans affect our evolution?
– Medical knowledge:
• Permits survival of individuals with genetic traits that
would not have otherwise survived
– Modern Transportation:
• Humans are less affected by geographic isolation
– Advanced Technology:
• Better nutrition and greater control over their
reproductive success
– Genetic Engineering:
• May lead to the appearance of new traits and the
elimination of others