A105 Lectures 5 & 6, January 27-29, 1997:

Evolutionary Genetics:

Mechanisms of Inheritance, and Implications for Our Future

Darwin had a mechanism for evolutionary change he called Natural Selection, but he didn't know how inheritance worked. Now we do. Three phases in our accumulating knowledge:

• Principles of Inheritance (1850s, Gregor Mendel)
• Discovery of Genetic Code (1953, Watson, Crick, et al)
• Human Genome Project

Mendel's contribution:

• Principles of Segregation and Independent Assortment (discreet traits called "Mendelian traits"
• difference between phenotype and genotype (via dominant and recessive traits)
• examples: hybrid peas; Sickle Cell anemia; Huntington's disease

Genetic Code:

• chromasomes are composed of DNA which controls protein synthesis (sequencing of Amino Acids)
• a GENE is the DNA needed to code for a single protein
• each sequence of 3 bases on the DNA molecule codes for a single Amino Acid
• 4 bases in combinations of 3 mean there are 64 possible codes for 20 Amino Acids... so the genetic code is redundant
• a mutation is a mistake in the replication of DNA... can be a single base substitution, or more complex
• the function of most of our DNA is unknown ... may be "junk DNA" ... but mutations can still occur in this inter-genic DNA and be inherited
• we still have limited knowledge of genetic code for specific traits... out of ~100,000 human genes, about 400 have been located

Human Genome Project:

• every individual's DNA is unique... goal is to sequence the human genome for medical knowledge
• genetic markers for particular Mendelian traits have been discovered
• repeated variations in the intergenic DNA occur at known locations, called VNTRs (Variable Number Tandem Repeats) and form basis for "DNA Fingerprinting"
  • can be used for identifying individuals within families (e.g. paternity)
  • has been used for forensic identification (e.g. matching DNA in blood in criminal investigations)... which can be problematic if the population reference DNA sample is poorly defined
• has demonstrated that human populations vary remarkably little, genetically, compared to other living species, and that the classification of people by "race" does not match genetic patterns. "Race" applied to humans is basically a cultural-social-political classification scheme, not a biological one. The superficial polygenic traits, like skin color or facial features, often used to artificially define "races" vary continuously across all human population groups according to geography and climate.

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Useful sources of information about the Human Genome Project and genetics on the WWW:

• Follow this WWW link to the Online Human Genome Map (Science Magazine) Click on "Featured Genes" link to see the list of examples and link to descriptions of inherited genetic conditions that have been identified, such as Huntington's disease, Cistic fibrosis, and forms of breast cancer.
• Link to Stanford's Human Genome Center, and read a recent interview with David Botstein, chairman of Stanford's Department of Genetics, about the impact of the Human Genome Project on the human future.
• The National Human Genome Research Institutute.
• Human Genome Project:
• The ethics of biotechnology and the human genome
• learn more about Gregor Mendel at MendelWeb.
• Read an interview with Francis Crick, one of the discoverers of DNA
• A summary of current research on nucleic acids
• 2 Descriptions of DNA structure (#2)
• How can genetic knowledge influence animal conservation efforts? Read about Dwindling Rhino Genes
• DNA fingerprinting (#2; #3) and forensics

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Last updated: 27 January 1997
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