02BIS1012013XLinkLect3

Bis101001spring2013genesandgeneexpressionrlrodriguez

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Unformatted text preview: rgan’s X-linked-Hemizygous Hypothesis ­ From these results, Morgan hypothesized: q q The gene for eye-color in Drosophila is on the The Drosophila chromosome that determines femaleness (X). chromosome In the case of males, only one copy of the eye color gene In is present. This is called "hemizygous." "hemizygous ­ Although Morgan was originally a critic of the Chromosome Although Theory, his experiments with eye-color in Drosophila provided Drosophila some of the first evidence in support of the Chromosome Theory of Inheritance. BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 17 Morgan’s Interpretation of Crosses BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 18 Attached X Experiments ­ However, this was genetic evidence. Cytological However, evidence was needed to convince the scientific community that genes were on chromosomes. This genes This evidence was provided by Morgan's wife, Mary and his graduate student, Calvin Bridges, who were working with a special mutant of Drosophila called "attached Drosophila attached X." ." ­ In the oocytes of these flies, the two X chromosomes In could be seen to be connected at their ends. As a result, the X-linked traits of the mother (e.g., white eyes) were always passed on to the daughter (never always to the son. BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 19 Morgan/Bridges Attached X Experiment Morgan/Bridges ­ In reciprocal In experiments using “attached X mutants, the eye color gene is always passed from the mother to the daughter but never to the son. the BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 20 Human Color Blindness — X Linked ­ A number of traits and number diseases are linked to the X chromosome in humans. One example is red/green color blindness, a recessive trait. Approximately 8% of all males experience one of two forms of color blindness. With protanopia (25% of all protanopia color blind males) red and green are seen as green. With deuteranopia, (75% of deuteranopia (75% all color blind males) red and green are seen as red. Color-blind Color-blind Color-blind Color-blind Color-blind Color-blind Colorblind Color-blind Colorblind BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez All sons, All color-blind color-blind 21 Well-Known Single Gene Disorders Disease Disease Effect Frequency Thalassemia (Chr. 11 or 16, rec.) Defect in alpha or beta hemoglobin genes 1/10 Italians Sickle-Cell Anemia (Chr. 11, rec) Abnormal hemoglobin shape, Malaria resistance 1/625 African Americans Cystic Fibrosis (Chr. 7, rec.) Defective Cell membrane protein; excessive Defective mucus, respiratory disease mucus, 1/3000 Whi...
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This note was uploaded on 02/12/2014 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

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