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Unformatted text preview: 5-Oct-09Gardiner1Chromosomes and InheritanceText Book Chapter 12•It was not until 1900 that biology finally caught up with Gregor Mendel.•Independently, Karl Correns, Erich von Tschermak, and Hugo de Vries all found that Mendel had explained the same results 35 years before.•Still, resistance remained about Mendel’s laws of segregation and independent assortment until evidence had mounted that they had a physical basis in the behavior of chromosomes.•Mendel’s hereditary factors are the genes located on chromosomes.Introduction•Around 1900, cytologists and geneticists began to see parallels between the behavior of chromosomes and the behavior of Mendel’s factors.–Chromosomes and genes are both present in pairs in diploid cells.–Homologous chromosomes separate and alleles segregate during meiosis.–Fertilization restores the paired condition for both chromosomes and genes.Mendelian inheritance has its physical basis in the behavior of chromosomes during sexual life cycles5-Oct-09Gardiner4Fig. 12-10, p. 244RrYyRY rY Ry ryB I O L O G Y 0 2 35-Oct-09Gardiner5Thomas Hunt Morgan•first to associate a specific gene with a specific chromosome in the early 20th century.•Like Mendel, Morgan made an insightful choice as an experimental animal, Drosophila melanogaster, a fruit fly species that eats fungi on fruit.5-Oct-09Gardiner6Drosophila melanogaster•small and easily reared in the laboratory. •short life cycle. A new generation every two weeks. •a female lays hundreds of fertilized eggs during her brief life span. The resulting large populations make statistical analysis easy and reliable. •giant ("polytene") chromosomes - salivary glands of the mature larvae.B I O L O G Y 0 2 35-Oct-09Gardiner70.5mm4.5 mm2 mm•Morgan spent a year looking for variant individuals among the flies he was breeding.–He discovered a single male fly with white eyes instead of the usual red.•The normal character phenotype is the wild type.•Alternative traits are mutant phenotypes. Fig. 12.7•When Morgan crossed his white-eyed male with a red-eyed female, all the F1offspring had red eyes,–The red allele appeared dominant to the white allele.•Crosses between the F1offspring produced the classic 3:1 phenotypic ratio in the F2offspring.•Surprisingly, the white-eyed trait appeared only in males.–All the females and half the males had red eyes.•Morgan concluded that a fly’s eye color was linked to its sex....
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This note was uploaded on 11/03/2009 for the course BIOLOGY 1223 taught by Professor Gardiner/lajoie during the Fall '09 term at UWO.
- Fall '09