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Genetics: A Conceptual Approach

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Chapter 9 Chromosome Variation Dr. Ed Otto George Mason University
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Key objectives To examine the different types of chromosomal mutations, including: - rearrangements - aneuploidy - polyploidy To understand the phenotypic effects of these mutations To understand their effects on meiosis To understand the role chromosomal mutations play in evolution
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Mutations ____________ are heritable change in genetic information Many mutations have detrimental effects and are the source of human diseases On the other hand… mutations are also the source of all new genetic variation, the raw material of evolution
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Classes of Mutations Historically, mutations have been divided into those that affect a single gene ( ______________ ) and those that affect the number and structure of chromosomes ( ________________________ ) In this chapter, we will examine chromosomal mutations; we will cover gene mutations in Chapter 18
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Chromosomal Mutations
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Karyotypes A complete set of chromosomes possessed by an individual is called its _____________ A karyotype is usually presented as a picture of metaphase chromosomes lined up in descending order of size Karyotypes are prepared from actively dividing cells, such as white blood cells
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Chromosomal Mutations Chromosomal mutations can be grouped into 3 categories: 1)Chromosome rearrangemnt – alter the structure of the chromosome; for example a piece of the chromosome is deleted 1)aneuplidy - the number of individual chromosomes is altered; one or more individual chromosomes are added or deleted 1)polyploidy – one or more complete sets of chromosomes are added
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1. Chromosomal Rearrangements
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Chromosomal Rearrangements Chromosomal rearrangements alter the structure of chromosomes The four major types of rearrangements are: a. Duplications a. Deletions a. Inversions a. Translocations
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a. Duplications A Duplication is a mutation in which part of the chromosome has been doubled
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Duplications If the duplicated region is immediately adjacent to the original segment, it is a Tandem Duplication AB*CDEFG AB*CDEFEF G If the duplication is located some distance from the original segment, it is a Displaced Duplication AB*CDEFG AB*CDEFGEF A duplication can be in the same orientation as the original segment, or inverted. An inverted duplication is called a Reverse Duplication AB*CDEFG AB*CDEFFE G
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Effects in Meiosis Individuals heterozygous for a duplication have one unmutated chromosome and one chromosome with a duplication In heterozygotes, problems arise in chromosome pairing during prophase I because the two chromosomes are not homologous throughout their length. - In this case, the pairing requires that one or both of the chromosomes loop and twist so that these regions are able to line up - The appearance of this characteristic loop is one way to detect duplications
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Phenotypic Effects Duplications may have major effects on phenotypes For example, the Bar mutation in Drosophila produces a bar shaped eye rather than oval The Bar mutation results from
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