Question

A group of transposable elements described as retroelements encompass

• A. P elements in Drosophila; LINES but not SINES in humans
• B. Copia elements in Drosophila; SINES but not LINES in humans
• C. Copia element in Drosophila; LINES as well as SINES in humans
• D. P elements in Drosophila; LINES as well as SINES in humans

Hint:

Remember the key distinction: Retroelements use an RNA intermediate and reverse transcriptase ('retro' = backwards from RNA to DNA). DNA transposons move directly as DNA. Key examples are Copia/LINES/SINES for retroelements and P elements for DNA transposons.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Transposable elements (TEs) are DNA sequences that can change their position within a genome. They are broadly classified into two major classes. The question asks to identify examples belonging to the class known as retroelements.
Class I TEs (Retroelements or Retrotransposons): These move via a "copy-and-paste" mechanism. They are first transcribed into an RNA intermediate, which is then reverse-transcribed back into DNA by an enzyme called reverse transcriptase. This new DNA copy is then inserted into a new location in the genome. Class II TEs (DNA Transposons): These move via a "cut-and-paste" mechanism, where the DNA element is excised from its original location and inserted elsewhere, a process catalyzed by an enzyme called transposase. Step 2: Detailed Explanation:
Let's classify the elements mentioned in the options:
P elements in Drosophila are classic examples of Class II DNA transposons. They move via a "cut-and-paste" mechanism. Copia elements in Drosophila are LTR-retrotransposons, which are a type of Class I retroelement. LINES (Long Interspersed Nuclear Elements) in humans are non-LTR retrotransposons, a major type of Class I retroelement. SINES (Short Interspersed Nuclear Elements) in humans are also non-LTR retrotransposons (Class I). They are "non-autonomous," meaning they rely on the machinery (like reverse transcriptase) provided by other elements like LINES to move. Now let's evaluate the options based on this classification:
(A) is incorrect because P elements are DNA transposons, not retroelements. (B) is incorrect because both SINES and LINES are retroelements in humans. (C) is correct. It correctly identifies the Copia element as a retroelement in Drosophila and both LINES and SINES as retroelements in humans. (D) is incorrect because P elements are DNA transposons. Step 3: Final Answer:
The group of transposable elements described as retroelements includes the Copia element in Drosophila and both LINES and SINES in humans.