• Alfred Sturtevant and the First
Genetic Map
• Genes That Assort Independently
and Those That Don’t
• Linkage and Recombination
Between Two Genes
Notation for Crosses with Linkage
Complete Linkage Compared with
Independent Assortment
Crossing Over with Linked Genes
Calculation of Recombination
Frequency
Coupling and Repulsion
The Physical Basis of Recombination
Predicting the Outcome of Crosses
with Linked Genes
Testing for Independent Assortment
Gene Mapping with Recombination
Frequencies
Constructing a Genetic Map with
Two-Point Testcrosses
• Linkage and Recombination
Between Three Genes
Gene Mapping with the Three-Point
Testcross
Gene Mapping in Humans
Mapping with Molecular Markers
• Physical Chromosome Mapping
Deletion Mapping
Somatic-Cell Hybridization
In Situ Hybridization
Mapping by DNA Sequencing
Alfred Sturtevant
and the First Genetic Map
In 1909, Thomas Hunt Morgan taught the introduction to
zoology class at Columbia University. Seated in the lecture
hall were sophomore Alfred Henry Sturtevant and freshman
Calvin Bridges. Sturtevant and Bridges were excited
by Morgan’s teaching style and intrigued by his interest in
biological problems. They asked Morgan if they could work
in his laboratory and, the following year, both young men
were given desks in the “fly room,” Morgan’s research laboratory
where the study of Drosophila genetics was in its
infancy (see p. 000 in Chapter 4). Sturtevant, Bridges, and
Morgan’s other research students virtually lived in the laboratory,
raising fruit flies, designing experiments, and discussing
their results.
In the course of their research, Morgan and his students
observed that some pairs of genes did not segregate
randomly according to Mendel’s principle of independent
assortment but instead tended to be inherited together.
Morgan suggested that possibly the genes were located on
the same chromosome and thus traveled together during
meiosis. He further proposed that closely linked genes—