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February 23, 2009

February 23, 2009. Objective : Discuss the effects of nondisjunction Drill: What is crossing over? What phase of meiosis does it occur?. Nondisjunction. Review: What is a mutation?. Mutation: A change in the nucleotide sequence of DNA A single nucleotide change can have serious effects.

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February 23, 2009

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  1. February 23, 2009 • Objective: Discuss the effects of nondisjunction • Drill: What is crossing over? What phase of meiosis does it occur?

  2. Nondisjunction

  3. Review: What is a mutation? • Mutation: A change in the nucleotide sequence of DNA • A single nucleotide change can have serious effects

  4. Chromosomal mutation • A chromosomal mutation involves a change in the structure or number of chromosomes • 4 types of chromosomal mutations: • Deletion: loss of all or part of a chromosome • Duplication: extra copy of all or part of a chromosome • Inversion: reverses the direction of parts of a chromosome • Translocation: part of one chromosome breaks off and attaches to another chromosome

  5. Nondisjunction Normal meiosis • Other types of chromosomal mutations alter the number of chromosomes found in the cell. • Nondisjunction: The failure of homologous chromosomes or sister chromatids to separate during meiosis. • Produces gametes that have too many or too few chromosomes

  6. Nondisjunction

  7. Disorders due to Nondisjunction • In humans, a zygote with 45 chromosomes has only one copy of a particular chromosome monosomy • In humans, a zygote with 47 chromosomes has three copies of a particular chromosome trisomy • Example Down syndrome (trisomy 21)

  8. Nondisjunction in the Sex Chromosomes • Nondisjunction can also affect the sex chromosomes, where there can be too many or too few X or Y chromosomes (XX- normal female, XY-normal male) • Examples of disorders: • XXY (Klinefelter’s syndrome) • XO (Turner’s syndrome)

  9. Karyotype • Karyotype: a picture of chromosomes in a dividing cell that are arranged in pairs by size. • First 22 pairs are autosomes • Last pair are the sex chromosomes

  10. Karyotype A * Normal male

  11. Karyotype B * Turner’s syndrome * Only 1 sex chromosome (X)- XO * Webbed neck, short stature, and infertility * Female

  12. Karyotype C * Cri du chat syndrome * Deletion of short arm of chromosome 5 * Distinctive cry, low birth weight, respiratory problems, may have a shortened lifespan * Female X Y

  13. Karyotype D * Klinefelter’s syndrome * 2 X chromosomes and 1 Y (XXY) * Tall, sterile, feminine characteristics, sometimes mentally retarded * Male

  14. Karyotype E * Normal female

  15. Karyotype F * Down syndrome * 3 copies of chromosome 21 (Trisomy 21) * Mental retardation, characteristic facial features, short stature, and heart defects * Male

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