Genome - total dna sequence of an organism. Humans have 20,500 genes, same range as mice. Fewer than 7% of protein families appear to be vertebrae specific. Human genome is 3 billion base pairs in length. Gregor mendel: austrian priest who carried out experiments in plant breeding (pea plant experiments, learning about inheritance), father of genetics . Pre-mendel: inheritance assumed to be through blending (blue + red = purple), incorrect assumption. Mendel: genetic info inherited in discrete units, units do not blend. Dominant allele masks effect of other recessive alleles inherited. The masked allele is the recessive allele. Genotype - inherited genetic makeup of an organism, cannot be seen. Phenotype - how genotype is expressed physically, can be seen. Mendelian traits are discrete traits, resulting from action of single gene at single place on a chromosome. Complex traits are controlled by many different genes at two or more places. Polygenic traits - many genes, one effect.