BI321Sp08 lecture 05

BI321Sp08 lecture 05 - Emails/Announcements Results for...

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Emails/Announcements • Results for vote: • 23 want to leave early • 22 want a break • ????
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Sex determination varies across species What is aneuploidy? • A nucleus is euploid if it contains some multiple of the haploid set of chromosomes • A nucleus is aneuploid if it does NOT contain some multiple of the haploid set of chromosomes • Aneuploid nuclei have missing or extra chromosomes
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What are the consequences of sex chromosome nondisjunction? Houston, we have a problem: aneuploidy for the X in men… PAR (pseudoautosomal region) PAR SRY (Sex-determining region of the Y) MRY (Male-specific region of the Y)
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Why is X-linked inheritance important? • Confirms the chromosomal theory of inheritance by showing that Mendel’s heritable factors (genes) reside on chromosomes • Shows that X-linked genes show a special kind of transmission (“criss-cross” inheritance) Lecture 5: Human Pedigree Analysis Human genetics, inheritance of disease genes Text readings: Chapter 2, pp 61 – 75; do problems 29, 31, 37, 38, 39, 40, 42, 43, 44, 47, 48, 49, 50, 52, 54, 57 Chapter 3, pp 89 – 97; 102 – 109; do problems 1, 2, 3, 7, 9, 10, 14, 18, 19, 20, 27 Chapter 16, pp 555 - 572
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Recessive X-linked disorders • Because males are hemizygous, they will be predominantly affected. • Examples of X-linked disorders include red-green color blindness, Fragile X syndrome, Hemophilia A, and Duchenne muscular dystrophy Color blindness Gene map locus Xq28. Color vision depends on the absorption of light by visual pigments contained within specialized types of cells in the eye called photoreceptors. Rod cells are used for vision in dim light and don’t detect color. Cone cells detect color: there are three different kinds of cone cells in the eye; the brain interprets color by integrating input from all three types. There are a number of different color vision defects, but red-green color blindness results from genetic defects on the X chromosome, and are up to 20X more common in males.
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Fragile X syndrome Gene map locus Xq27.3 affects 1/4000 male births (1/6000 female births) (CDC) Expansion of CGG nucleotide repeats in the promoter of the FMR1 gene (product of this gene involved in translational regulation) 70-500 repeats are OK (“premutation”) Expansion of 600 or more result in the disorder (full mutation) Females heterozygous for a full mutation and a premutation will likely exhibit the disorder
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Hemophilia A Gene map locus Xq28 affects between 1/5000 and 1/10,000 males in most populations X-linked recessive bleeding disorder Due to a deficiency in the activity of coagulation factor VIII Treatment is by replacement of Factor VIII (blood transfusions) There are other variants of this disease (some of them autosomal) Duchenne muscular dystropy • Gene map locus Xp21.2, 12q21 • 1/1,000 to 1/10,000…depends… • Mutations in Dystrophin (HUGE gene) • Dystrophin normally plays a critical role in transmitting signals for muscle contraction • Symptoms include progressive muscular degeneration • Death usually by ~17 years • Females heterozygous have milder symptoms
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This note was uploaded on 04/29/2008 for the course BIOL 321 taught by Professor Schultze during the Spring '08 term at Western Washington.

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BI321Sp08 lecture 05 - Emails/Announcements Results for...

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