SC.912.L.15.15

1. Mutations 2. Genetic Recombination (sexual reproduction)

 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?