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Chromosomal Abnormalities Changes in chromosome structure or number.

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Presentation on theme: "Chromosomal Abnormalities Changes in chromosome structure or number."— Presentation transcript:

1 Chromosomal Abnormalities Changes in chromosome structure or number

2 Alteration of chromosome number ▫Nondisjunction- homologous chromosomes don’t separate during meiosis I or sister chromatids don’t separate during Meiosis II ▫trisomy  cells have 3 copies of a chromosome ▫monosomy  cells have only 1 copy of a chromosome

3 Alteration of chromosome number all with incorrect number1/2 with incorrect number error in Meiosis 1 error in Meiosis 2

4 Karyotyping Somatic cells are isolated Treat with a chemical to stimulate mitosis Photograph taken of metaphase chromosomes Arrange chromosomes according to: ▫ Size ▫Banding pattern ▫Centromere position Observe the patterns http://learn.genetics.utah.edu/content/begin/traits/ karyotype/http://learn.genetics.utah.edu/content/begin/traits/ karyotype/

5 What observations can you make? Normal Human MaleNormal Human Female

6

7 Down syndrome Trisomy 21 ▫3 copies of chromosome 21 ▫1 in 700 children born in U.S. Chromosome 21 is the smallest human chromosome ▫but still severe effects Frequency of Down syndrome correlates with the age of the mother

8 Down syndrome & age of mother Mother’s age Incidence of Down Syndrome Under 30<1 in 1000 301 in 900 351 in 400 361 in 300 371 in 230 381 in 180 391 in 135 401 in 105 421 in 60 441 in 35 461 in 20 481 in 16 491 in 12

9 Human chromosome disorders High frequency in humans ▫most embryos are spontaneously aborted ▫alterations are too disastrous Certain conditions are tolerated ▫upset the balance less = survivable ▫but characteristic set of symptoms = syndrome

10 Alterations of chromosome structure deletion ▫loss of a chromosomal segment duplication ▫repeat a segment inversion ▫reverses a segment translocation ▫move segment from one chromosome to another

11 Alterations of Chromosome Structure


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