chapter 15 - Chromosomes Chromosome mutation is the primary...

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1 Chromosomes Chromosome mutation is the primary source of genetic variability… Natural selection acts on phenotypes, but genes persist only if the phenotype of the gene-holder is viable . Genes on Chromosomes genes are located on chromosomes chromosomes Æ Mendel’s laws Æ segregate and assort independently Pp x Pp YyRr x YyRr 3: 1 P Generation Gametes Meiosis Yel ow-round seeds ( YYRR ) Fertilization Green-wrinkled seeds ( yyr ) Al F1 plants produce yel ow-round seeds ( YyRr ) Meiosis Two equal y probable ar angements of chromosomes LAW OF INDEPENDENT ASSORTMENT F1 Generation LAW OF SEGREGATION at metaphase I Anaphase I Metaphase I Fertilization among the F1 plants F2 Generation Gametes P Generation Gametes Meiosis Yel ow-round seeds ( YYRR ) Fertilization Green-wrinkled seeds ( yyrr ) Al F 1 plants produce yel ow-round seeds ( YyRr ) Al F 1 plants produce yel ow-round seeds ( YyRr ) Meiosis Two equal y probable arrangements of chromosomes at metaphase I Ah LAW OF INDEPENDENT ASSORTMENT F 1 Generation LAW OF SEGREGATION Anaphase Metaphase I Gametes Thomas H. Morgan Æ fruit fly Drosophila Morgan’s experiments Æ chromosomes are the location of Mendel’s heritable factors Morgan identified wild type and mutant phenotypes in Drosophila
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2 Wild type Æ red eye Mutant Æ white eye male flies white W eyes x female flies red eyes F 1 generation Æ red eyes W + F 2 generation Æ 3 red : 1 white eye ratio, but only males had white eyes Mating between wild-type and mutants Morgan’s H 1 Æ white-eye mutant allele must be located on the X-chromosome sex-linked traits! P Generation F 1 Generation F 2 Generation P Generation How are sex-linked genes inherited? F 1 Generation Ova (eggs) Sperm F 2 Generation Ova (eggs) Sperm Drosophila ’s chromosomes Y and X P Generation P Generation F 1 Generation P Generation F 1 Generation F 2 Generation
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3 P Generation P Generation F 1 Generation Ova (eggs) Sperm P Generation F 1 Generation Ova (eggs) Sperm F 2 Generation Ova (eggs) Sperm Sex-Linked Genes Sex-chromosomes have genes for many characters unrelated to sex Genes on X or Y chromosomes Æ sex-linked genes Sex-linked genes follow specific patterns of inheritance Hemophilia X-linked Color blindness X-linked Duchenne muscular dystrophy X-linked Example of an X-chromosome linked trait: gene for H emophilia within the British Royal Family.
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This note was uploaded on 04/16/2008 for the course BIO 131 taught by Professor Paz y mino during the Fall '08 term at UMass Dartmouth.

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chapter 15 - Chromosomes Chromosome mutation is the primary...

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