ch12-humangenetics - Chromosomes and Human Genetics Chapter...

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Chromosomes and Human Genetics Chapter 12
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Genes Units of information about heritable traits In eukaryotes, distributed among chromosomes Each has a particular locus Location on a chromosome
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Homologous Chromosomes Homologous autosomes are identical in length, size, shape, and gene sequence Sex chromosomes are nonidentical 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 same or different
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Studying Human Genetics Studying Human Genetics is much more complicated than using other model systems (e.g. Pea Plants) Humans reproduce slowly, have few offspring, and it is unethical to breed humans for experiments There are many techniques that are used to study human genetics indirectly Karyotypes Pedigree analysis Linkage maps
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Karyotype Picture of an individual’s chromosomes Making a Karyotype: Metaphase chromosomes are fixed and stained Chromosomes are photographed through microscope Photograph of chromosomes is cut up and arranged to form karyotype diagram
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Sex Chromosomes Autosomes Karyotype
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Sex Chromosomes Discovered in late 1800s Mammals, fruit flies XX is female, XY is male In other groups XX is female, XY male Human X and Y chromosomes function as homologues during meiosis
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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) Figure 12.5 Page 198
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The Y Chromosome Fewer than two dozen genes identified One is the master gene for male sex determination SRY gene (sex-determining region of Y) SRY present, testes form SRY absent, ovaries form
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The X Chromosome Carries more than 2,300 genes Most genes deal with nonsexual traits Genes on X chromosome can be expressed in both males and females
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Pedigree A chart showing the genetic connections between individuals A genetic family tree Often groups of people whose heritage is well
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ch12-humangenetics - Chromosomes and Human Genetics Chapter...

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