lab 10 - Human Genetics Cytogenetics Study of chromosome...

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Unformatted text preview: Human Genetics Cytogenetics Study of chromosome structure, function and evolution Karyotypes used to detect chromosomal abnormalities Not used to detect abnormalities with individual genes Chromosome Preparation Select actively mitotic tissue fetal, skin, cheek cells Add mitotic spindle inhibitor (compound that stops replication in metaphase) Place cells in hypotonic sol'n to swell nuclei Isolate nuclei centrifuge Transfer to glass slide Nuclei break Chromosomes spread in identifiable groups Chromosomes stained to allow bands to be seen Homologous chromosomes paired to form a karyotype Karyotype can be used to determine Sex Chromosome abnormalities X and Y chromosomes Last "pair on karyotype" Male XY Female XX An easier way to determine sex Nuclei from cheek cells stained In females the 2nd X chromosome has condensed and appears as a dark spot near the nuclear membrane Barr body Barr body # = # of X - 1 Mendelian Inheritance in Humans Many human traits can be used to demonstrate Mendel's law of segregation. Traits controlled by a single gene, each with 2 alleles. An individual can be: Homozygous dominant Homozygous recessive Heterozygous Your phenotype is a description Your genotype is D- (DD or Dd) or dd Dominance does not mean better or more common Dimpled chins Free ear lobe Attached ear lobe Widow's peak Bent little fingers Not bent little fingers Non-hitchhiker's thumb Hitchhiker's thumb Non pigmented iris Pigmented iris Nondisjunction and Translocation Mistakes in meiosis can result in unequal distribution of the chromosomes in the newlyformed daughter cells Nondisjunction: failure of chromosomes to separate during meiosis May occur during Meiosis I or Meiosis II Can occur with sex chromosomes or autosomal chromosomes Triple X XXX -- Turner's XO Klinefelter's XXY -- Jacob's - XYY Translocation- the transfer of a portion of one chromosome to another, usually nonhomologous chromosomes Some cases of trisomy 21 are caused by a large portion of chromosome 21 becoming attached to chromosome 15 Some genetic mistakes are just not viable and the zygote will be spontaneously aborted Genetic Pedigree Shows inheritance patterns for a specific trait in a family Allows genetic counselors to determine a couple's risk of having children that would inherit a detrimental trait Constructed with a standard set of symbols Read history on p 188 and construct a pedigree Pseudoisochromate plates Forensic Science DNA testing can identify an individual with a much higher degree of certainty, because the DNA sequence of every person is unique (except for identical twins). There are several DNA fingerprinting tests Restriction Fragment Length Polymorphisms RFLPs Restriction sites are deleted or added through mutations The same restriction enzyme is used to cut the DNA and the band patterns are compared Closely related individuals will have similar band patterns At least 5 RFLP markers are tested in crime cases The more markers used the less likely it is anyone else These test can be used for paternity or to identify victims of disasters Variable Number of Tandem Repeats VNTRs Another method In between genes there are long sequences of base pairs that do not code for anything Short sequences of (5-10) bp repeated over and over How many repeats varies greatly between individuals The amount of repeats between restrictions sites produces different fragment lengths between individuals VNTRs can also be used for paternity Shown on the next page are the VNTR patterns for the Smith family of 6. Mrs. Smith [blue], Mr. Smith [yellow], D1 (the Smith's biological daughter), D2 (Mr. Smith's step-daughter, child of Mrs. Smith and her former husband [red]), S1 (the Smith's biological son), and S2 (the Smith's adopted son, not biologically related [his parents are light and dark green]). Procedure 191 Procedure 179 Observe cheek cells on demo scopes 185 Complete tables Observe karyotypes side counter Biology image bank biologyimages.tamu.edu User name: bio123 Password biology 111 ...
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This note was uploaded on 11/11/2008 for the course BIOL 111 taught by Professor Rizzo during the Fall '07 term at Texas A&M.

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lab 10 - Human Genetics Cytogenetics Study of chromosome...

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