Karyotypes – Flashcards
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What is a karyotype?
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Photomicrograph of a dividing cells chromosomes
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What is a karyotype used for?
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Used to identify chromosomal abnormalities
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How many chromosomes are in humans?
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44 autosomes and 2 sex chromosomes
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When was the correct number of human chromosomes established?
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Not until 1956 due to the clumping of chromosomes in dead tissue
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How are chromosomes paired and grouped?
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Paired with homologue and grouped according to length and location of centromere
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Preparation of a karyotype part 1
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Acquire white blood cells
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Preparation of a karyotype part 2
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Add chemical (colchicine) to break down spindle fibers which effectively halts all cells at metaphase and kills them
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Preparation of karyotype part 3
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Add distilled water and centrifuge to separate white blood crlls
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Preparation of karyotype part 4
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Fix with alcohol and stain
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Preparation of karyotype part 5
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Photograph burst cells using microscope (ones in metaphase) and then enlarge
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Preparation of karyotype part 6
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Cut out chromosomes and match pairs
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Preparation of karyotype part 7
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Sort by decreasing soze
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Who is this tool (the karyotype) used by?
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Genetic counsellors and cytogeneticists
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Where is the karyotype used extensively?
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In the HGS (Human Genome Study)
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What type of chromosomal abnormalities can be detected by using a karyotype?
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Sex cells with abnormal number of chromosomes due to nondisjunction (usually causes embryos that are not viable)
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Down Syndrome
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Usually an extra chromosome in chromosome pair 21. Sometimes can be caused by translocation of chromosome 21-14
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Symptoms of Down Syndrome
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Mild to severe retardation, flat face, thick tongue & neck, abnormalities of organs, generally early death.
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Klinefelter's Syndrome
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Extra X Chromosome
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Symptoms of Klinefelter's Syndrome
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Small breasts, reduced fertility, and long limbs, male
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Examples of chromosomal abnormalities
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Can also have XXXY and XXXXY
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XXX and X (Turner's Syndrome)
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Generally normal females with reduced fertility
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Deletion
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Small pieces of chromosome get deleted during Interphase. Usually lethal.
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Duplication
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Pieces of chromosome that got deleted are incorporated into its homologue, essentially duplicating that potion of the chromosome
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Translocation
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Small pieces of chromosome are deleted form one chromosome &I moved to another non-homologus chromosome
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Inversion
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Small piece of chromosome "flips" in place
