# DBT JRF 2020 — Question 87

Exam: DBT JRF 2020 · Section: B · Topic: Molecular Biology · Difficulty: Medium

## Question

For a tetranucleotide sequence, the number of possible combinations using A, T and G are

## Options

- **A.** 512
- **B.** 27
- **C.** 256
- **D.** 81

## Answer

Option D

## Explanation

Tetranucleotide sequences using only 3 of the 4 standard DNA/RNA bases (here: A, T, and G — cytosine excluded). For each of the 4 nucleotide positions, there are 3 choices (A, T, or G). By the fundamental counting principle for independent events: Total combinations $= 3^4 = 3 \times 3 \times 3 \times 3 = 81$ .

Source: https://mypyqbuddy.com/questions/for-a-tetranucleotide-sequence-the-number-of-possible-6a05a8a02adafec47029326f