Lecture Chapter 15

Lecture Chapter 15 - Chapter 15 The Chromosomal Basis of...

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Chapter 15 The Chromosomal Basis of Inheritance • Relating Mendelism to Chromosomes • Sex Chromosomes • Errors and Exceptions in Chromosomal Inheritance • Mendel’s results revealing paired characters and their behavior in genetic crosses lay dormant until their rediscovery and confirmation in 1900 • Another group of scientists working on cells, described chromosomes- their paired nature in diploids and behavior during meiosis and fertilization. • The parallels were made and the chromosome theory of inheritance started to take shape Gene probe shows the location of a gene on each of two homologs What stage in the cell cycle is the cell in? What do you notice about the nature of the hybridization?
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• A dihybrid cross diagrammed to show the genes in chromosomes (black lines) and the behavior of the chromosomes during meiosis. The Chromosomal basis of Mendel’s laws 15.2 Independent assortment Segregation T. H. Morgan • The founder of Drosophila (fruit fly) genetics • Pictured in ‘the fly room’ at Columbia • Nobel laureate 1933
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Why flies? • Small • Cheap to keep • Prolific • Short generation time • Only 4 chromosomes • Small genome His students " I suddenly realized that the variations in the strength of linkage already attributed by Morgan to difference in the spatial separation of the gene offered the possibility of determining sequence in the linear dimensions of a chromosome. I went home and spent most of the night (to the neglect of my undergraduate homework) in producing the first chromosome map. . . . " (Sturtevant, A.H., Unpublished interview with G.E. Allen) Sturtevant
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white the first fly mutant • Discovered in 1910 • Called white for the mutant phenotype w =mutant gene w + = normal or wild-type gene • This notation is used in Drosophia genetics 15.3 • Morgan crossed the w mutant to red eyed females (w + ) • All the F 1 were red eyed – Is w recessive or dominant? • Set up sib matings from the F 1 • The F 2 had a 3:1 ratio of red eyes to white eyes • But all females were red eyed and half the males were white eyed – How can you explain the results?
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shows a pattern of sex-linked inheritance 15.4 Dominant or recessive? Sexlinked or autosomal?
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Lecture Chapter 15 - Chapter 15 The Chromosomal Basis of...

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