Biology 214/414 Homework #1 Due 8-28-09 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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