Biology 214/414
Homework #1
Due 82809
Solution
For each question, show all your work and/or explain your answer.
1.
Consider the fruit fly,
Drosophila
, that has a (chromosome)
n
number of 4.
a.
How many
chromatids
are there in an interphase somatic cell (somatic cells
include all body cells except gametes or gamete producing cells) after DNA
replication but before mitosis?
If n = 4, there are 4 pairs of chromosomes, or 8 chromosomes total/cell (the
diploid number).
After replication, each chromosome will have two identical
sister chromatids, which will not be separated from each other until after
mitosis.
So the total number of chromatids/cell at this point in time will be 2 X 8 = 16.
b.
How many
chromatids
are there in a gamete producing cell after the
first
meiotic division (and cytokinesis) are completed?
In interphase of meiosis, each chromosome will be replicated and so as the cell
proceeds into the first meiotic division it will have 8 chromosomes (4 pairs of
homologues), each with two chromatids.
The first meiotic division reduces the
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 Spring '06
 Stark
 Cell Cycle, Interphase, Mitosis, meiotic division

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