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CH 12 ADDITIONAL_MATERIAL_student_outline - Chromosomes and...

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Chromosomes and Human Genetics Chapter 12 (Additional Topics: no additional readings, but focus on THIS lecture material for exam questions)
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Chromosomes & Cancer Some genes on chromosomes control cell growth and division If something affects chromosome structure at or near these loci, cell division may spiral out of control This can lead to cancer
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Philadelphia Chromosome First abnormal chromosome to be associated with a cancer Reciprocal translocation of chromosome pieces; #9 had piece of #22 attached to it Abnormal protein produced as a result Causes chronic myelogenous leukemia (CML)
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Re-examining Mendel’s Work By 1882, Flemming observed threadlike chromosomes in nuclei of dividing cells By 1887, Weisman suggested that meiosis halves the # of chromosomes when gametes produced By 1900, Mendel’s work was finally appreciated
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Homologous Chromosomes Homologous autosomes (non-sex chromosomes) are identical in length, size, shape, and gene sequence Sex chromosomes are non-identical but still homologous Homologous chromosomes interact, then segregate from one another during meiosis
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Alleles Different molecular forms of a gene Arise through mutation Diploid cell has a pair of alleles at each locus Alleles on homologous chromosomes may be the same or different 0
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a b c a b c A B C A B C A B C a b c a b c b c A A B C B C a 0 How Crossing Over Creates New Allele Combinations in Gametes These segregate into separate gametes
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Sex Chromosomes Discovered in the late 1800s Mammals, fruit flies XX is female, XY is male In other groups, XX is male, XY is female Human X and Y chromosomes function as homologues during meiosis 0
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Karyotype Preparation - Stopping the Cycle Cultured cells are arrested at metaphase by adding colchicine This is when the chromosomes are most condensed and the easiest to identify 0
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Karyotype Preparation Arrested cells are broken open Metaphase chromosomes are fixed and stained Chromosomes are photographed through microscope Photograph of chromosomes is out up and arranged to form karyotype diagram 0
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0 Karyotype.swf (use Apple Quicktime to open and view)
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Sex Determination X X Y X XX XY XX XY X X Y X x x eggs sperm female (XX) male (XY) 0
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0 Sex Determination.swf (use Apple Quicktime to open and view)
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The Y Chromosome Fewer than two dozen genes identified on the Y One is the master gene for male sex determination SRY gene (sex-determining region of Y) SRY present, testes form SRY absent, ovaries form 0
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Effect of Y Chromosome 10 weeks Y present Y absent 7 weeks birth approaching appearance of structures that will give rise to external genitalia appearance of “uncommitted” duct system of embryo at 7 weeks Y present Y absent testis ovary testes ovaries 0
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The X Chromosome Carries more than 2,300 genes Most genes deal with non-sexual traits Genes on X chromosome can be expressed in both males and females 0
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