Chapter 15

Chapter 15 - Chapter 15 CHROMOSOMAL BASIS OF INHERITANCE I....

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Chapter 15 CHROMOSOMAL BASIS OF INHERITANCE I. Mendelian inheritance has it physical basis in the behavior of chromosomes during sexual life cycles (see fig. 15.2). A. Chromosomes and genes are both paired in diploid cells. B. Chromosomes separate during the formation of gametes and allele pair segregation. C. Fertilization restores diploid condition for both chromosomes and genes. Chromosomes and genes Mendel’s studies published in 1865 Cytologist work out the basics of mitosis in 1875 Cytologist work out the basics of meiosis 1890 - Meiosis doesn’t occur often Mendel’s work “rediscovered” 1900 II. From these observations the chromosomal theory of inheritance arose. A. A genetics and cytology time line Don’t know what chromosome are yet But do know that something’s carrying the DNA GENETICS CYTOLOGY 1860's Mendel proposes discrete inherited factors segregate and assort independently during gamete formation 1875 Cytologist work out the basics of mitosis 1900 Mendel’s work “rediscovered” 1890 Cytologist work out the basics of meiosis 1902 Cytology and genetic converge as behavioral similarities between inherited factors and the chromosomes become apparent I. Linked genes tend to be inherited together because they are located on the same chromosome. A. Linked genes – genes located on the same chromosome 1. Genes on the same chromosome don’t assort independently. Gene on chromosome – when chromosome moves, gene moves 2. Since independent assortment doesn’t occur, the 9:3:3:1 ratio is not seen Chromosome doesn’t have 1 gene but more than 1 Linking Genes to Chromosomes: The Work of Morgan – 15.1.4 I. Thomas H. Morgan traced a gene to a specific chromosome A. Morgan worked with fruit flies, Drosophila melanogaster Short life cycle – reproduce quickly Produce a lot of offspring Short number of chromosome B. Morgan bred flies and looked for variants. Note on genetic symbols: 1. An allele is named after the non- wild-type (means something unusual) , or mutant phenotype discovered. 2. The wild-type allele is dominant and the mutant allele is recessive 3. The wild-type trait is designated with a superscript + sign. 4. For eye color the wild-type phenotype is red (see fig. 15.3), the mutant color is white and white is recessive 5. Therefore the symbol for this gene is w i. A fly with white eyes = w ii. A fly with red eyes = w+ Name after recessive phenotype C. Why fruit flies? 1. 100’s of offspring
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This note was uploaded on 03/18/2010 for the course BIOL 1201 taught by Professor Wishtichusen during the Spring '07 term at LSU.

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Chapter 15 - Chapter 15 CHROMOSOMAL BASIS OF INHERITANCE I....

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