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Probability and Genetics. Elementary outcomes and events.
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Elementary outcomes and events. E.g., suppose we perform the cross , and we're interested in the genotype of offspring. Each offspring produced by this cross must have genotype , , or . These represent the ELEMENTARY OUTCOMES of the experiment; the elementary outcomes are mutually exclusive (e.g., an offspring could not be both genotype and genotype ). We might be interested in the EVENT that `the offspring has at least one copy of the allele'. This event consists of two elementary outcomes (i.e., genotype , or genotype ). Each elementary outcome has an associated probability, based on underlying laws (e.g., of Mendelian inheritance).
ADDITION RULE (`Or'). • Used to determine probability of an event that consists of two or more mutually exclusive elementary outcomes. • Probabilities of mutually exclusive elementary events are added. • E.g., in the example above, the probability of the three elementary events are . The probability of the event `` or '' is .
MULTIPLICATION RULE (`And'). • Used to determine the probability of an event that consists of two or more independent events. • Probabilities of independent events are multiplied. • E.g., Suppose parental genotype is . In terms of gametes produced, mutually exclusive elementary outcomes include: production of the gamete; production of the gamete. Both of these event occur with probability . Probability that the first gamete examined from this parent is and a second gamete, drawn independently of the first, is equals .