- Prepared slides of Drosophila (fruit fly) salivary gland chromosomes
- Genetic map of polytene chromosome bands
- Examine the slides for the presence of bands. Select a single chromosome
spread demonstrating all 4 chromosomes and draw the complete structure.
- Label each of the 4 chromosomes of the fruit fly, as well as the chromocenter
of the connected chromosomes.
- Compare your drawings to the genetic map for Drosophila.
The glands of dipterans (flies) have a useful characteristic for analysis of gene
location on chromosomes. During their mitotic division, the normal division of
the chromosomes is aborted and the replicated chromosomes remain as an
integral unit. The chromosome content thus increases geometrically and produces
“giant” polytene chromosomes. The chromosomes remain attached at a point
where the centromeres fuse, at the chromocenter. This is clearly observed in the
chromosomes of the fruit fly salivary gland tissue. The fruit fly chromosomes
are ideal specimens since they are in a near constant state of prophase and are
incapable of further division. Because they have been extensively analyzed for
their genetic composition, colinear maps of genes within genetic linkage groups
have been produced and correlated with the physical location of a band on the