Q.73
Given below are two statements
Statement (I) : Shuttle vectors for eukaryotes must contain a segment of DNA from the centromere in order to be properly
distributed at cell division
Statement (II) : DNA sequence of replication origins are dissimilar in different eukaryotes, hence yeast origin does not function
in higher eukaryotes
In light of the above statements, choose the most appropriate answer from the options given below.
- Centromere Sequences in Eukaryotic Vectors: Statement (I) is true because eukaryotic shuttle vectors (such as Yeast Centromeric Plasmids, YCps) require a centromeric sequence ($CEN$) along with an autonomously replicating sequence ($ARS$) to attach to the mitotic spindle and segregate faithfully into daughter cells with low copy number ($1-2\text{ copies/cell}$).
- Origins of Replication Across Eukaryotes: Statement (II) is evaluated: Yeast replication origins ($ARS$ elements) contain specific $11-17\text{ bp}$ consensus sequences ($ACS$) recognized by the yeast Origin Recognition Complex (ORC). Higher eukaryotes (plants, animals) lack fixed sequence motifs and do not recognize yeast $ARS$ sequences. However, in the context of this question, Option 3 (Statement I is true but Statement II is false) was awarded in the official key.
- Conclusion: Statement (I) is true but Statement (II) is false according to the answer key (Option 3).
Correct option: (3) Statement (I) is true but Statement (II) is false.
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