Which Transposition Event Increases DNA Content in a Cell?

Transposons, also known as “jumping genes,” are DNA sequences capable of moving from one genomic location to another. They are broadly classified into two types:

• Class I: Retrotransposons (copy-and-paste)

• Class II: DNA transposons (cut-and-paste)

Let’s explore the options:

1. Ac/Ds Elements

• These are DNA transposons found in maize.

• Operate via cut-and-paste mechanism.

• No net increase in DNA content as the element is excised and reinserted elsewhere.

• Incorrect Answer

2. Mu Elements

• Another type of DNA transposon in maize.

• Also functions via cut-and-paste.

• Though they can amplify during replication, they do not inherently increase DNA content in the same manner as retrotransposons.

• Incorrect Answer

3. P Elements

• Found in Drosophila melanogaster.

• Also cut-and-paste transposons.

• Do not increase total DNA content.

• Incorrect Answer

4. LINEs (Long Interspersed Nuclear Elements)

• Retrotransposons in humans and other eukaryotes.

• Move via a copy-and-paste mechanism using an RNA intermediate.

• A new copy is inserted without removing the original.

• Result: Increase in total genomic DNA.

• Correct Answer

Why LINEs Increase DNA Content

LINEs (especially LINE-1 in humans):

• Are autonomous retrotransposons that encode reverse transcriptase and endonuclease.

• Transcribe into RNA and are reverse transcribed back into DNA.

• This DNA is inserted elsewhere in the genome, adding extra copies, hence increasing the overall DNA content.

Correct Answer:

4. LINEs

This is the only option among the given choices that utilizes a replicative (copy-and-paste) mechanism, resulting in an increase in DNA content in a given cell.