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Understanding Genomic Imprinting and Chromosomal Abnormalities in Genetics

This chapter explores the complexities of genomic imprinting, where only one parent's copy of an imprinted gene is expressed due to epigenetic silencing. It highlights examples like the Igf2 gene in mice, illustrating how phenotypes vary based on parental inheritance. The chapter further delves into nondisjunction and aneuploidy, discussing conditions such as Turner and Klinefelter syndromes. Additionally, it covers partial chromosomal changes like deletions and duplications, and the concept of non-nuclear inheritance, emphasizing the maternal role in mitochondrial DNA transmission.

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Understanding Genomic Imprinting and Chromosomal Abnormalities in Genetics

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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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