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Mutations and Other Exceptions to Mendel

Mutations and Other Exceptions to Mendel. Chapter 15. Genomic Imprinting. For most genes, we inherit two working copies -- one from each parent But with imprinted genes, we inherit only one working copy

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Mutations and Other Exceptions to Mendel

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  1. Mutations and Other Exceptions to Mendel Chapter 15

  2. Genomic Imprinting • For most genes, we inherit two working copies -- one from each parent • But with imprinted genes, we inherit only one working copy • Depending on the gene, either the copy from mom or the copy from dad is epigenetically silenced • Silencing usually happens through the addition of methyl groups during egg or sperm formation.

  3. Genomic Imprinting Example: Igf2 • Insulin-like growth factor 2 (Igf2) is needed in mice for normal growth and development • In crosses between wild type and homozygous recessive dwarf mice, individuals produced heterozygous offspring • Offspring differed in phenotype depending on whether the gene was maternal or paternal

  4. Nondisjunction • Chromosomes fail to separate properly in meiosis I or II • Results in aneuploidy: abnormal chromosome number

  5. Whole Chromosome Changes: Aneuploidy • Monosomy • Only 1 chromosome of a pair is present • Ex: Turner syndrome • Trisomy • 3 copies of a chromosome are present • Ex: Klinefelter syndrome • Polyploidy • More than 2 complete sets of chromosomes • Ex: Tympanoctmysbarrerae,plants

  6. Partial Chromosome Changes • Deletion • Part of a chromosome segment is removed • Duplication • Part of a chromosome segment is repeated

  7. Partial Chromosome Changes • Inversion • Part of a chromosome segment is reversed within a chromosome • Translocation • Part of a chromosome segment is moved to another non-homologous one

  8. Karyotypes • Picture of chromosomes arranged in pairs • Allows scientists to see: • Sex of individual • Any chromosomal abnormalities

  9. Non-Nuclear Inheritance • Mitochondrial DNA (mDNA or mtDNA) • Inherited from mother ONLY • Sperm’s mitochondria lost after fertilization • 3 people, 1 baby

  10. Human Genetic Diseases • More to come….

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