Question

question 2
you have devised a system that allows you to stain adenine bases with a visible purple dye. you place some yeast cells into a growth media containing the dye solution and allow the dye to become incorporated into both strands of the double helices. you then remove a single yeast cell from the dye during g1 phase and allow it to go through two rounds of cell division in a growth medium that contains no dye, but has all other necessary components needed for replication. all four cells are back in g1 phase at the end of this experiment. if you isolate all the dna from the four cells, what percentage of those dna molecules will contain some purple dye?
0%
25%
50%
75%
100%
question 3
which of the following describes the dna in sister chromatids?
they are produced by semiconservative dna replication and they are attached to each other from the start of g2 phase until the start of anaphase.
they contain significantly different dna sequences
they are produced by semiconservative dna replication
they are attached to each other from the start of g2 phase until the start of anaphase.
they contain significantly different dna sequences, they are produced by semiconservative dna replication and they are attached to each other from the start of g2 phase until the start of anaphase.

Explanation:

Question 2

Step1: Understand DNA replication mode

DNA replication is semi - conservative. Each original strand serves as a template for a new strand.

Step2: Analyze the first round of replication

After the first round of replication (from 1 DNA molecule to 2 DNA molecules), each new DNA molecule has one old (stained) strand and one new (unstained) strand.

Step3: Analyze the second round of replication

After the second round of replication (from 2 DNA molecules to 4 DNA molecules), out of the 4 DNA molecules, 2 will have one old (stained) strand and one new (unstained) strand, and 2 will have two new (unstained) strands.

The percentage of DNA molecules with some purple dye is \(\frac{2}{4}\times100\% = 50\%\)

• Sister chromatids are produced by semi - conservative DNA replication. During S phase, DNA replicates, and each chromosome now consists of two sister chromatids.
• They are attached to each other from the end of S phase (not exactly the start of G2, but after S phase completion) until the start of anaphase when the cohesin complex is cleaved and they separate.
• Sister chromatids have identical DNA sequences (assuming no mutations during replication).

Answer:

50%

Question 3