2_2009_Inheritance_8_27_09

2_2009_Inheritance_8_27_09 - Biological Sciences 120L...

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1 Biological Sciences 120L General Biology: Organismal Biology and Evolution Lecture 2 (8/27/09) K. Heidelberg 2 Mon. 12-1 Wed. 5-6 Wed. 6-7 Fri. 2-3 usc.edu/si Bio120sileaders@gmail.com (put “Sean” in the subject) Sean’s SI Sessions Supplemental Instruction Help
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3 Other Announcements 4 Scope of this Course Evolution How are traits passed down? Why do many antibiotics no longer work? Is modern human behavior a product of past evolutionary history? Diversity What is meant by diversity? What is the importance of biodiversity? How have modern molecular techniques revolutionized our view of biodiversity? Ecology What small and large-scale factors affect ecology? How are humans affecting our environment?
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5 Lecture 1: Patterns of Eukaryotic Inheritance • Chapter 14 6 Patterns of Inheritance In the 1800s - lots of unknowns and different beliefs Genetic principles accounting for the passing of traits from parents to offspring For example: Blending hypothesis The idea that genetic material from the two parents blends together (blue and yellow paint blend to make green)
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7 Enter Gregor Mendel… Austrian Monk Lived 1822-1884 Fig. 14-1 •Developed laws of inheritance by breeding peas in carefully planned experiments Work not appreciated until ~1900 8 Mendel’s application of the scientific approach • Used a scientific approach to identify two laws of inheritance • Discovered the basic principles of heredity, and put forward the “particulate hypothesis” -- the idea that parents pass on discrete heritable units (genes)
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9 Why Peas? Why Peas? – Many distinct characters with heritable traits – Mating can be controlled – Easy to do both cross fertilization and self- fertilization – Fairly short generation time – Early experiments showed interesting (predictable) patterns TECHNIQUE Parents (P) Stamens Carpel 1 2 3 4 Figure 14.2 RESULTS First generation (F 1 ) Figure 14.2 P Generation (true-breeding parents) Purple flowers White flowers F 2 Generation F 1 Generation (hybrids) All plants had purple flowers P P w w Pw Pw Pw Pw P w P w PP Pw Pw ww Inquiry A typical experiment with true breeding parents and one factor Fig. 14.3 F 1 =100% purple plants F 2 = 3:1 (75% purple;25% white)
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11 Heritability Homologous pair of chromosomes Purple allele White allele Flower color gene locus Fig 14.4 Genes of most multicellular organisms are carried on chromosome pairs in the cell nucleus - one set almost identical set inherited from each parent. Genotype : The set of genes an organism inherits (homozygous vs. heterozygous). Phenotype : The expressed appearance of a trait. Alleles : variations in a gene’s nucleotide sequence Each pair has to 2 copies of almost every gene - one from each parent. Alleles may be identical or slightly different. Sequence differences may lead to different forms of the same trait (e.g.
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2_2009_Inheritance_8_27_09 - Biological Sciences 120L...

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