9: Chromosomal Disorders
- Page ID
- 171279
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- 9.1: Changes in Chromosome Number
- Nondisjunction produces cells or gametes with extra or missing chromosomes. Comparing errors in mitosis and meiosis explains how aneuploidy arises and why altered gene dosage can reduce viability.
- 9.2: Changes in Chromosome Structure
- DNA break repair and unequal crossing over can produce deletions, duplications, inversions, and translocations. Tracing rearranged chromosomes through meiosis distinguishes balanced from unbalanced products and explains reduced fertility.
- 9.3: Chromosome Abnormalities in Humans
- Karyotype notation records chromosome number, sex chromosomes, and chromosome abnormalities. Human examples connect extra, missing, or rearranged material with gene dosage and its effects on development and fertility.
- 9.4: Diagnosing Human Chromosome Abnormalities
- Chromosome staining, fluorescence in situ hybridization (FISH), and DNA measurements detect different kinds of chromosome abnormalities. Examples show how to interpret chromosome patterns and probe signals and why changes in DNA amount cannot reveal every rearrangement.
- 9.5: Gene Balance
- Changing gene copy number can disrupt the relative amounts of interacting proteins. Gene balance explains why gaining or losing individual chromosomes can be more harmful than changing the number of complete chromosome sets.
- 9.6: X-inactivation
- X-inactivation reduces expression from additional X chromosomes and produces cell lineages with different active X chromosomes. Barr bodies and patchy cat coats connect chromosome dosage with visible patterns of gene expression.

