Polytene chromosomes Flashcards
what was the purpose of this lab?
description and isolation of giant chromosomes from the salivary glands of Drosophila. The usefulness of the polytene chromosome in determining gene location on chromosomes is discussed
as the drosophila larva grows, why do the cells and enlarge and chromosomes within replicate many times?
because the larva keeps the same number of cells but needs to make much more protein
what is the result of the drosophila growing and keeping the same number of cells but needing to make much more protein?
in some tissues, cells enlarge and the chromosomes within replicate many times
what is a polytene chromosome
a thick chromosome that has been replicated many times
T or F: a polytene chromosome can be seen under the light microscope
true
do homologous chromosomes pair up before or after the production of polytene chromosomes?
before
what is the number of DNA strands in each salivary gland chromosome after pairing and repeated replication?
1024 (512 strands in each homologue)
why is the X chromosome easily spotted in male flies?
it has no homologue (it’s only half the thickness of the other chromosomes)
what is the chromocenter?
the heterochromatic regions surrounding the centromere of polytene chromosomes are all joined together to form the chromocenter
why is the small Y chromosome in male flies not visible?
because it’s incorporated into the chromocenter
how many autosome and sex chromosome pairs do flies have?
3 autosomes, 1 pair of sex chromosomes
a standard map of drosophila polytene chromosomes divides the genome into ___ numbered divisions
102
describe the numbered divisions of the chromosomes
1-20 on the X, 21-60 on chrom. 2, 61-100 on chrom. 3, and 101 and 102 on chrom. 4
how is each division divided?
into lettered subdivisions (A-F)
how are the lettered subdivisions divided?
subdivided into numbered bands
