Question: A geneticist models the expression level of a drought-resistant gene as a function $ f(n) $ satisfying $ f(n + 1) = 3f(n) - 4 $, with $ f(1) = 5 $. Find $ f(5) $.

Fri, 01 May 2026 08:51:52 +0000

**Why This Simple Equation Is Resonating in Genetic Research and Beyond**
In a time when breakthroughs in sustainability and biotechnology dominate headlines, understanding how gene expression evolves mathematically offers unexpected insight. The function $ f(n + 1) = 3f(n) - 4 $, starting with $ f(1) = 5 $, models a dynamic where expression levels grow rapidly under consistent conditions—mirroring how genetic traits enhance resilience, like drought resistance. This pattern isn’t just theoretical; it reflects real-world biological responses critical for future crop innovation and medical research. Curious readers are drawn to this blend of math and biology, especially as climate challenges accelerate demand for robust, gene-informed solutions. This question is gaining traction not only in academic circles but also among industry innovators and informed policymakers seeking predictive models for genetic behavior. Its straightforward recursive structure invites both curiosity and analysis—perfect for mobile users scrolling through evolving scientific knowledge. **The Recursive Model: How Does Expression Grow?**
Let’s break down the equation: $ f(n + 1) = 3f(n) - 4 $. Each step multiplies the prior expression level by three and subtracts four—a pattern common in systems showing accelerating growth under controlled factors. With $ f(1) = 5 $, we calculate each next value incrementally: - $ f(2) = 3 \cdot 5 - 4 = 15 - 4 = 11 $
- $ f(3) = 3 \cdot 11 - 4 = 33 - 4 = 29 $
- $ f(4) = 3 \cdot 29 - 4 = 87 - 4 = 83 $
- $ f(5) = 3 \cdot 83 - 4 = 249 - 4 = 245 $