If you expose human tissue culture cells (for example,HeLa cells) to 3H-thymidine just as they enter Sphase, then wash this material off the cells and letthem go through a second S phase before looking atthe chromosomes, how would you expect the 3H to bedistributed over a pair of homologous chromosomes?(Ignore the effect recombination could have on thisoutcome.) 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) someother pattern? Choose the correct answer and explainyour reasoning. (This problem extends the analysisbegun in Solved Problem III.)
Genetic Recombination
Recombination is crucial to this process because it allows genes to be reassorted into diverse combinations. Genetic recombination is the process of combining genetic components from two different origins into a single unit. In prokaryotes, genetic recombination takes place by the unilateral transfer of deoxyribonucleic acid. It includes transduction, transformation, and conjugation. The genetic exchange occurring between homologous deoxyribonucleic acid sequences (DNA) from two different sources is termed general recombination. For this to happen, an identical sequence of the two recombining molecules is required. The process of genetic exchange which occurs in eukaryotes during sexual reproduction such as meiosis is an example of this type of genetic recombination.
Microbial Genetics
Genes are the functional units of heredity. They transfer characteristic information from parents to the offspring.
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. (This problem extends the analysis
begun in Solved Problem III.)
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