Answer:
According to Chargaff's rule, if a DNA strand has 30% guanine before to semi-conservative replication, the percentage of thymine that will have each new strand after replication will be 20% (option A).
Explanation:
A DNA molecule stores the genome of a living organism in a specific sequence of its nitrogenous bases adenine, guanine, cytosine and thymine. By knowing the percentage of a nitrogenous base in the DNA, the percentage of the other bases can be established using Chargaff's base pair rule.
Chargaff was able to establish that in a DNA molecule the ratio purine:pyrimidine is 1:1, so there must be the same amount of guanine as cytosine and a similar amount of adenine for thymine, taking into account the complementarity of the bases.
According to the base pair rule, if in a DNA strand there is 30% guanine, in the molecule there is:
- <em>
Guanine 30%.
</em>
- Cytosine 30%.
- <em>Thymine 20%.
</em>
- <u>Adenine 20%</u>.
- Total ..... 100%
In this case, Chargaff's rule is useful to determine the percentage of thymine that each new strand will have after replication, corresponding to 20%.
