Summary
This 1915 book, co-authored by Thomas Hunt Morgan and his students, established the chromosome theory of inheritance by demonstrating that genes are physically located on chromosomes in linear order. The central thesis is that Mendelian factors (genes) correspond to specific chromosomal loci, and that genetic linkage, crossing over, and recombination reflect physical exchanges between homologous chromosomes. The authors present experimental evidence from breeding studies with the fruit fly *Drosophila melanogaster*, showing that traits like eye color and wing shape segregate according to predictable patterns tied to chromosome behavior during meiosis. A reader takes away a mechanistic understanding of heredity as a material process, where genetic maps can be constructed from recombination frequencies, and where sex-linked traits are explained by X-chromosome inheritance. The book solidified Morgan’s “fly room” discoveries into a coherent framework that merged Mendelism with cytology.
Key concepts
- Linkage — The tendency for genes located on the same chromosome to be inherited together, deviating from Mendel’s law of independent assortment.
- Crossing over — The reciprocal exchange of chromosomal segments between homologous chromosomes during meiosis, producing new combinations of linked alleles.
- Genetic map — A linear diagram of gene positions on a chromosome, constructed from recombination frequencies between linked genes.
- Sex linkage — The inheritance pattern of genes located on the X chromosome, causing traits to appear more frequently in one sex (e.g., white eyes in male *Drosophila*).
- Chromosome theory of inheritance — The principle that genes reside on chromosomes, and that chromosome behavior during meiosis explains Mendelian segregation and independent assortment.
- Recombination frequency — The percentage of offspring showing recombinant phenotypes, used to infer relative distances between genes on a chromosome.
From the book
Title: The Mechanism of Mendelian Heredity (1915, with A.H. Sturtevant, H.J. Muller, and C.B. Bridges) by Thomas Hunt Morgan
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