Human Genetics Problem Set

Problem 12 Tutorial: Somatic cell hybrids

By examining a number of somatic-cell hybrid lines for enzyme activities and their human chromosome constitution, scientists can determine

on which human chromosome the gene for a particular enzyme is located

Cell fusion

Somatic cells from two animal species may be fused to form a hybrid cell in culture. Nuclei can subsequently fuse to form a somatic-cell hybrid. Human and rodent cell fusions are important reagents for human genetics. The resulting human-rodent hybrid cells will often lose most of the chromosomes from one of the species, e.g. most of the human chromosomes, but continue to express the genes from all remaining chromosomes.

Tay-Sachs disease

Tay-Sachs disease is a genetic disease caused by a defect in the enzyme for hexosaminidase A. Normal hexosaminidase A activity can be assayed in extracts from cultures of somatic cell hybrids.

Assume that you are studying three different somatic cell hybrid cultures.

One cell line has only human chromosomes 1, 15 and 9.
A second has 15, 10, and 12.
A third cell line has only human chromosomes 4, 15, and 17.

All three cell lines have human hexosaminidase A activity. You could conclude that the gene for the human enzyme was located on chromosome 15, the only human chromosome common to all three somatic cell hybrid cultures.

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Revised: November 5, 1998
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