Transcript Increasing genetic variation through mutations and genetic

SC.912.L.15.15
Mutations
Genetic Recombination (sexual
reproduction)
1.
2.
 Mutations
are the raw material of
evolutionary change.

changes in the nucleotide sequence of DNA
 Mutation
introduces new variation into a
population.

cause new genes and alleles to arise
 This
variation is adaptive if it helps members
of a population adjust to specific
environmental conditions.
 Change
in a morphological trait. This refers
to an obvious change in some physical
characteristic of an organism. (for example,
short plants instead of tall)
 Change
in behavior. In one example,
Drosophila (fruit fly) mating behavior was
found to be affected by a mutation. Mutant
male flies were no longer able to distinguish
between males and females, and tried to
mate with any fly available!
 Lethality.
Some mutations are lethal to an
organism, like the yellow coat color allele in
mice or the Huntington's allele of humans

When lethal, the allele is not usually passed
on, as the organism will usually die before
reproducing


Sexual reproduction can shuffle existing alleles into new
combinations
In organisms that reproduce sexually, recombination of
alleles is more important than mutation in producing the
genetic differences that make adaptation possible
 Variation
in individual genotype leads to
variation in individual phenotype
 Not all phenotypic variation is heritable
 Natural
selection can only act on variation
with a genetic component
 Think
about this….
A Deadly Example of Evolution in Progress
HIV = Human Immunodeficiency Virus
The causative agent of AIDS (Acquired Immune Deficiency Syndrome)
HIV is a type of retrovirus that attacks cellular components of the
human immune system by reversing the normal process of DNA
transcription.
Through genetic analysis
of the viral RNA, a family
tree of HIV and related
viruses can be
constructed.
This phylogeny shows
that monkeys were the
original source of the
virus that jumped to
humans and became HIV.
We can plot the
genetic differences
among strains of HIV
over the 20 years of
available data.
Extrapolating a best-fit
line to those data
allows us to estimate
the time when there
was zero genetic
difference within a
strain.
Dates the common
ancestor of HIV and
SIV back to ~1930.
What does HIV/AIDS teach us about evolution?
Due to the reverse transcription process, the genetic
diversity of HIV increases substantially as the virus
spreads through a human population. Some variants of
the virus replicate while others die, and as a result the
composition of the population changes over time. That
is, the viral population evolves, and continues to do so at
an extremely rapid rate.
HIV’s potential for rapid evolution has profound consequences.
Within infected individuals HIV populations quickly evolve resistance to
antiretroviral drugs. Without these drugs, HIV populations continuously
evolve to evade the human host’s immune defenses.
HIV evolution is thus an example of natural selection in action
which emphasizes the importance of genetic variation and how
environments determine the direction of change.
 Write
a few sentences about how genetic
variation among the HIV’s (a virus)
population has allowed it to survive so long
in the human population, despite various
attempts from humans to develop a vaccine
to get rid of HIV.
 How does this relate to genetic variation in
the human population’s ability to survive
malaria?