if you expose human tissue culture cells (for example, HeLa cells) to 3 H-thymid
ID: 207665 • Letter: I
Question
if you expose human tissue culture cells (for example,
HeLa cells) to 3 H-thymidine just as they enter S phase,
then wash this material off the cells and let them go
through a second S phase before looking at the chromosomes,
how would you expect the 3 H to be distributed
over a pair of homologous chromosomes? (Ignore the effect recombination could have on this outcome.)
Would the radioactivity be in (a) one chromatid of
one homolog, (b) both chromatids of one homolog,
(c) one chromatid each of both homologs, (d) both
chromatids of both homologs, or (e) some other pattern?
Choose the correct answer and explain your
reasoning.
Explanation / Answer
In S phase chromosomes duplicate to form a copy and the copy remains attached as chromatids. During meiosis, the homologs come together. Now, since the first S phase was incubated in 3H, all the chromosomes will have one chromatid (the newer one) to bear 3H residues. Now when the homologs will come together each will have one chromatid to bear radioactivity. SO the answer is (c)
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.