Q.51 In a mouse genome, the numbers of functional
Vα, Jα, Vβ, Dβ, Jβ gene segments are
79, 38, 21, 2 and 11, respectively.
The total number of possible combinations for
αβ T cell receptors are
______ × 106.
Total Number of Possible αβ T Cell Receptor Combinations in Mouse Genome
The diversity of the adaptive immune system is generated through
V(D)J recombination. In T lymphocytes, the
αβ T cell receptor (TCR) is formed by rearrangement
of multiple gene segments. This article explains how to calculate
the total number of possible αβ T cell receptor combinations
in a mouse genome.
Correct Answer
138 × 106
Step-by-Step Explanation
1. α-Chain Combinations
The α-chain of the T cell receptor is formed by
Vα–Jα recombination.
α-chain combinations = Vα × Jα
= 79 × 38 = 3002
2. β-Chain Combinations
The β-chain is formed by
Vβ–Dβ–Jβ recombination.
β-chain combinations = Vβ × Dβ × Jβ
= 21 × 2 × 11 = 462
3. Total αβ T Cell Receptor Combinations
One α-chain pairs with one β-chain to form a complete αβ TCR.
Total combinations = 3002 × 462
= 1,386,924
4. Expression in Scientific Notation
1,386,924 ≈ 1.38 × 106
Final Answer
138 × 106
Key Takeaway
The vast diversity of T cell receptors arises from the combinatorial
joining of gene segments. Even without junctional diversity,
the mouse genome can generate over
138 million distinct αβ T cell receptors.
