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Introduction to Genetic Epidemiology
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Gregor Mendel and Mendelian Genetics
The first systematic study of mating genetics was carried out in the 1860s by the Austrian monk
Gregor Mendel. Mendel was working with pea plants at the time. He published a study showing
how living things inherit physical characteristics from their parents and pass them along to their
offspring. After thousands of experiments with peas, Mendel realized that individual traits were
inherited separately – a tall plant can have green or yellow peas, just as a tall person can have
brown hair or blonde.
His work was forgotten for a generation, not truly appreciated until some time after his death. It
formed the foundation of modern genetics and led to the notion that biological information is
transmitted in discreet packets that came to be called genes. By the 1920s, the concepts of
genetics were becoming clear and scientists knew that chromosomes were the structures inside
cells that contained the heritable factors which Mendel identified much earlier. The basic
heritable elements were called genes, and each gene exists in several slightly different forms
known as alleles.
It is understood now that inheriting a particular allele can sometimes increase the chance of
inheriting another, or affect how and when a trait is expressed in an individual’s physical,
biochemical, and physiological makeup.
Mendel’s conclusions:
• Each physical characteristic corresponds to one “factor”
• Factors come in pairs
• Only one of each pair is passed on to the next generation
• It’s equally probable that one “factor” or the other will be passed on.
• Some “factors” are dominant, some are recessive.