Chapter 12: Chromosomal Basis of Inheritance

Chromosomal Basis of Inheritance begins by detailing the structure of the genome and the cell cycle, differentiating between the growth phases of interphase and the nuclear division process of mitosis, which preserves genetic identity through stages such as prophase, prometaphase, metaphase, anaphase, and telophase. The text contrasts somatic division with meiosis, the two-step reduction division essential for sexual reproduction, emphasizing how homologous chromosome pairing, synapsis, and crossing-over in prophase I generate genetic diversity and result in haploid gametes. A major focus is placed on the Chromosome Theory of Inheritance, supported by the foundational work of Sutton, Boveri, and Thomas Hunt Morgan, whose experiments with Drosophila melanogaster demonstrated that specific genes reside on sex chromosomes. The summary explores various mechanisms of sex determination, including the mammalian XY system, the ZW system in birds, and the X-to-autosome ratio in insects and nematodes, while defining the concept of hemizygosity in heterogametic sexes. It further investigates the consequences of errors in chromosome segregation, such as nondisjunction, which leads to aneuploidy conditions like Turner syndrome and Klinefelter syndrome. Dosage compensation is also explained, particularly the mammalian mechanism of random X-inactivation and the formation of Barr bodies as described by the Lyon hypothesis. Finally, the chapter outlines the principles of pedigree analysis used to track inheritance patterns—including autosomal recessive, autosomal dominant, X-linked, and Y-linked traits—in human families.