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Errors in mitosis or meiosis can results in changes in phenotype

Errors in mitosis or meiosis can results in changes in phenotype. Breakage of a chromosome can lead to four types of changes in chromosome structure: Deletion removes a chromosomal segment Duplication repeats a segment Inversion reverses a segment within a chromosome

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Errors in mitosis or meiosis can results in changes in phenotype

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  1. Errors in mitosis or meiosis can results in changes in phenotype

  2. Breakage of a chromosome can lead to four types of changes in chromosome structure: • Deletion removes a chromosomal segment • Duplication repeats a segment • Inversion reverses a segment within a chromosome • Translocation moves a segment from one chromosome to another Alteration of Chromosome Structure

  3. Fig. 15-15 A B C D E F G H A B C E F G H Deletion (a) A B C D E F G H A B C B C D E F G H Duplication (b) A B C D E F G H A D C B E F G H Inversion (c) A B C D E F G H M N O C D E F G H (d) Reciprocal translocation M N O P Q R A B P Q R

  4. In nondisjunction, pairs of homologous chromosomes do not separate normally during meiosis • As a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy Abnormal Chromsome Number

  5. Alterations of chromosome number and structure are associated with some serious disorders • Some types of aneuploidy appear to upset the genetic balance less than others, resulting in individuals surviving to birth and beyond • These surviving individuals have a set of symptoms, or syndrome, characteristic of the type of aneuploidy Human disorders due to chromosomal alterations…

  6. Fig. 15-13-3 Meiosis I Nondisjunction Meiosis II Nondisjunction Gametes n – 1 n + 1 n – 1 n n n + 1 n + 1 n – 1 Number of chromosomes (b) Nondisjunction of sister chromatids in meiosis II (a) Nondisjunction of homologous chromosomes in meiosis I

  7. Aneuploidyresults from the fertilization of gametes in which nondisjunction occurred • Offspring with this condition have an abnormal number of a particular chromosome • Polyploidy is a condition in which an organism has more than two complete sets of chromosomes • Triploidy (3n) is three sets of chromosomes • Tetraploidy (4n) is four sets of chromosomes • Polyploidy is common in plants, but not animals • Polyploids are more normal in appearance than aneuploids

  8. Down Syndrome • Klinefelter Syndrome • Turner Syndrome • Jacob’s Syndrome (super male) • Edward’s Syndrome • Cri du chat (cry of the cat) Syndrome • Patau’s Syndrome • Wolf-Hirschhorn Syndrome Chromosome Number/Structure Disorders…

  9. Form groups • Select a Disorder (1st come 1st serve) • Research Disorder • Identify Problem • State Symptoms • Life expectancy • Treatments or Cures • Record info on poster paper • Share with class Assignment…

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