Chapter 6 Lecture Notes

Chapter 6 Lecture Notes - Cytogenetics: Karyotypes and...

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Unformatted text preview: Cytogenetics: Karyotypes and Chromosomal Aberrations Chapter 6 Chromosome Number Varies From table 6.1 Organism Human Chimpanzee Dog Housefly Corn Mouse Diploid Number 46 48 78 12 20 40 Haploid Number 23 24 39 6 10 20 Human Chromosomes Males have.... Females have... Gametes have.... Chromosome Structure Short arm called p Long arm called q Centromere is in the middle Used to denote gene locations p53 gene The Centromere Divides the Chromosome into Two Arms Fig. 6.2 Creating a Karyotype Fig. 6.6 Karyotype Fig. 6.3 Making Karyotypes Chromosomes collected from cells in ___________ of mitosis Chromosomes are: stained to give bands matched by: banding, length and centromere location Making Karyotypes Matched chromosomes sorted by size In humans: Chromsome 1 is longest Chromosome 22 is shortest X and Y determined by banding patterns Karyotype Analysis What we look for: # of chromosomes sex chromosomes missing/extra chromosomes any chromosomal aberrations Let's Paint: Use of Florescent Dye DNA can be "painted" with flourescent dye Each chromosome is unique Can determine if pieces of chromosomes get moved around translocation Chromosomal Painting Normal Cell Cancer Cell with Translocations Fig. 6.9 Any cell with a nucleus! Often examined cells: Cells Used for Chromosomal Analysis White blood cells Skin cells Tumor cells Fetal cells Collection of Fetal Cells Amniocentesis removal of fluid from around fetus around 16th week Chorionic villus removal of cells from placenta The baby's side 8 to 10 weeks, riskier to mom and baby Amniocentesis Fig. 6.10 Chorionic Villus Sampling Fig. 6.12 Chromosomal Abnormalities Polypoidy = Aneuploidy = Monosomy and trisomy Polypoidy Due to errors in: Mitosis Meiosis Problems with fertilization Triploidy Fig. 6.12 It is estimated that: Humans have high rate of aneuploidy Aneuploidy & Reproductive Failure 10x higher than other mammals, including primates 1 in 2 conceptions are aneuploid Aneuploidy and Nondisjunction Nondisjunction = Produces abnormal gametes Nondisjunction Fig. 6.14 Autosomal Trisomy Most are lethal Examples: Trisomy 13: Patau syndrome (47,+13) Trisomy 18: Edwards syndrome (47,+18) Trisomy 21: Down syndrome (47,+21) Autosomal Trisomy Fig. 6.16 First chromosomal abnormality discovered Down Syndrome in humans (1959) 1/900 live births Leading cause of mental retardation and heart defects in US Similar physical characteristics Trisomy 21 Risk for Autosomal Trisomy Fig. 6.19 Risk For Trisomy Why does the risk increase for women as they get older? Consequences of Aneuploidy Pregnancy loss Birth defects Cancer Sex Chromosome Aneuploidy 45, X 47, XXY 47, XYY Turner's syndrome Klinefelter syndrome XYY syndrome Turner's Syndrome: 45, X Need at least one X Sterile females, abnormal sexual devlopment No mental dysfunction Not common: 1/10,000 births XYY Syndrome: 47, XYY Rate: 1/1000 births Above average in height No established link with possible antisocial behavior Fig. 6.24 Male phenotype, onset after puberty Klinefelter Syndrome: 47, XXY Rate: 1/1000 births Low fertility Some mental dysfunction 60% = maternal nondisjunction Other forms XXYY, XXXY and XXXXY Chromosomal Abnormalities Deletions = Additions = Inversions = Translocations = Structural Abnormalities Fig. 6.25 Largescale deletions are lethal Deletions Deletion of short arm, #5: Cri du chat Affects motor and mental function Infant cry sounds like meowing cat Lost genes voice box development Types of Translocations Reciprocal Translocation = No information lost Robertsonian Translocation = part of chromosome is lost 5% of Down syndrome Uniparental disomy both chromosome Other Chromosomal Abnormalities copies from same parent Fragile sites, which are..... ...
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