Genetic Variation

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Genetic Variation
National DNA Day April 25, 2008

Presentation derived from Human Genetic Variation module created by the National Human Genome Research Institute through a contract with the National Institutes of Health, in partnership with BSCS and Videodiscovery Presentation intended for classroom use only

Human Genetic Variation
Genetics is the scientific study ofinherited variation Human genetics is the scientific study of inherited human variation We study this variation in order to better understand ourselves as a species and use this knowledge to improve our health and well-being

Understanding human genetic variation
Homo sapiens are a relatively young species We each have approximately 3x109 base pairs of DNA
We have not had much time to developgenetically and produce variations

And yet around the world, all populations of humans are essentially the same – the differences lie among individuals, not among populations

No two people, except for identical twins, are genetically identical Any two people have about 6X106 base pairs which are different; this may seem like a lot, but in fact is only 0.1% of the entire human genome.This is leading some geneticists to question the validity of defining race – the biological differences between the races are much fewer than the differences among individuals in one race

What are genetic variations?
Variations are simply differences in genetic sequence Variation can be seen at every genetic level:
In In In In In the the the the the DNA genes chromosomes proteins function ofproteins







Major types of genetic variations
Mutations – changes at the level of DNA; one or more base pairs has undergone a change; change could be at random or due to a factor in the environment Major deletions, insertions, and genetic rearrangements can affect several genes or large areas of a chromosome at once Polymorphisms –differences in individual DNA which are not mutations
Single-nucleotide polymorphisms (SNPs) are the most common, occurring about once every 1,000 bases or so Copy number variations – some DNA repeats itself (i.e. AAGAAGAAGAAG) and there can be variation in the number of repeats

Understanding human genetic variation
Most variation is “meaningless” – it does not affect our ability to survive oradapt
Example: “silent mutations” in DNA, which change the DNA, but does not change the amino acid the DNA codes for. Other mutations may change the amino acid sequence of a protein, but not the overall function of that protein Many polymorphisms do not seem to affect our survivability

Understanding human genetic variation
Some variation is positive – it improves our ability to survive or adaptMutations in the CCR5 gene provide protection against AIDS – makes it harder for HIV to bind to the surface of cells and infect them Genetic mutations which cause the disease sickle cell anemia have also been found to have a protective effect – individuals with sickle cell trait (i.e. carriers of the recessive gene) are less likely to die from the disease malaria, which is caused by parasitesand spread by mosquitoes

Understanding human genetic variation
And, of course, some variation leads to disease
Single-gene disorders like cystic fibrosis and Huntington disease We are also learning more about the contribution of genetic variation to more “common” conditions, such as heart disease, cancer, diabetes, and psychiatric disorders like schizophrenia and bipolar disorder; variationmay give us a predisposition to one of these conditions, though not the condition itself

Understanding human genetic variation
For those mutations/variations which make us more likely to develop a condition such as diabetes, environment also plays a key role. We now believe that genetics plays a part in virtually all human diseases, except perhaps trauma
Environment may be interacting with...
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