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PowerPoint Notes - PowerPoint Notes 23:43 Chapter 14:...

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Unformatted text preview: PowerPoint Notes 23:43 Chapter 14: Patterns of Inheritance Gregor Mendel • Austrian monk who lived from 1822- 1884 • Developed laws of inheritance • His work was not appreciated until after his death Why Peas? • Many distinct traits • Mating can be controlled • Easy to do both cross fertilization and self-fertilization • Fairly short generation time • Early experiments showed interesting pattern Mendel’s Model • Trait variation is due to alternative versions (alleles ) of heritable factors (genes ) • For each character an organism inherits two alleles, one from each parent • Dominant alleles mask recessive alleles • Two alleles for a heritable character segregate (separate) during gamete formation and end up in different gametes (Law of Segregation) Law of Independent Assortment Mendelian inheritance is governed by laws of probability • Alleles of one gene segregate into gametes independently of another gene’s alleles • Multiplication rule: The probability of independent events A and B both happening= P(A) * P(B) • Addition rule: The probability that either A or B happens= P(A) + P(B) The Spectrum of Dominance • Complete dominance • Codominance • Incomplete dominance Extending Mendelian genetics to traits controlled by two or more genes • Epistasis: One gene alters the phenotypic effect of another gene • Polygenic inheritance: One trait is controlled by many genes The Eugenics Movement • >60,000 involuntary sterilizations in the US • 33 states participated • Focused on prison inmates and the “feeble minded” Chromosomes We know now that Mendel’s “hereditary factors” are located on chromosomes • Early studies of meiosis showed that the behavior of chromosomes parallels the behavior of Mendel’s “factors” o Both chromosomes and “factors”: Present in pairs in diploid cells Segregate during meiosis Halve their copy numbers during meiosis and double their copy numbers at fertilization Thomas Hunt Morgan ’s fruit fly experiments provided the first strong evidence that genes are located on chromosomes • Why fruit flies? o Easy to rear in the lab o Short generation time (~10 days) o Abundant offspring (100s per mating) o Only 4 pairs of chromosomes o Numerous mutation stocks now available • What happens when genes are located on the same chromosome?...
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This note was uploaded on 02/03/2010 for the course BIO 120 taught by Professor Staff during the Fall '07 term at USC.

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PowerPoint Notes - PowerPoint Notes 23:43 Chapter 14:...

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