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Nondisjunction

Delve into the impacts of nondisjunction, explore different chromosomal mutations, and learn about disorders resulting from abnormal chromosome numbers in humans. Discover the significance of crossing over, meiosis phases, and genetic mutations.

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Nondisjunction

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  1. Nondisjunction

  2. Objective: Discuss the effects of nondisjunction • Answer: What is crossing over? What phase of meiosis does it occur?

  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 * Normal female

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

  13. Karyotype D * 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

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

  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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