Ch_9_PartA - Chapter 9 Chromosomal Variation Chromosomal...

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Chapter 9: Chromosomal Variation
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Chromosomal Morphology Metacentric Submetacentric Acrocentric Telocentric
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Recombination Homologous chromosomes pair in prophase I If crossing over occurs, ½ the gametes will be recombinant
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Chromosomal Rearrangements Alter the structure of the chromosome and include duplications, deletions, inversions, and translocations
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Duplication Part of the chromosome has been doubled AB CDEFG AB CDEFEF G tandem duplication – duplicated region is adjacent to original segment displaced duplication duplicated region is at a distance from original segment reverse duplication – duplicated region is inverted heterozygotes for a duplication require that the duplicated chromosome loops out during pairing in prophase I duplications can affect the phenotype
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Duplication – Bar mutation Bar mutation results in change in size and shape of eye in D. melanogaster the greater the number of copies the smaller the eyes Bar mutation results from a duplication on the X chromosome and is inherited as incompletely dominant abnormal gene dosage
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Duplication – Bar mutation Chromosomes do not align properly resulting in unequal crossover Double Bar female is created through unequal crossing over between chromosomes containing two copies of Bar
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Duplications Duplications can negatively affect the phenotype because of imbalances in the amount of gene products (abnormal gene dosage) e.g. Bar mutations in Drosophila Some duplications are beneficial and different gene copies are maintained over millions of years e.g. globins
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