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PowerPoint Notes - PowerPointNotes 23:43 Chapter14:...

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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
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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? o Morgan noticed that certain traits tend to be inherited together  Recombination      of Linked Genes: Crossing Over Morgan discovered that genes can linked, but the linkage was incomplete, as  evident from recombinant phenotypes
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