The lock of hair Jerome Morrow gives Vincent Freeman in *Gattaca* serves a dual purpose, being both a **practical necessity** within the world of the film and a profound **sentimental and symbolic gesture**.
The **specific details** of this act are as follows:
### 1. Practical Necessity (Final DNA Sample)
* **Sustaining the Identity:** Throughout the film, Vincent (an "In-Valid") relies on Jerome's (a "Valid") constant supply of high-grade DNA—including urine, blood, skin, and hair samples—to pass the rigorous genetic screening at the Gattaca Aerospace Corporation and live as "Jerome Morrow".
* **Continuation of the Deception:** Jerome, who plans to take his own life by the time Vincent launches into space, leaves the lock of hair in an envelope as a final, fresh, and easily preserved DNA sample. This ensures Vincent has a supply of "Jerome's" genetic material to maintain the deception, even after Jerome's death and destruction of his remains.
### 2. Sentimental and Symbolic Gesture
* **A Token of Remembrance and Devotion:** Historically, a lock of hair is a traditional sentimental gift, symbolizing love and remembrance, especially before an impending separation. By giving Vincent a lock of hair instead of just a vial of blood, Jerome transforms a functional item into a **personal, non-functional memento**. The screenplay explicitly states that the lock of hair was included solely for its **sentimental value**.
* **Vicarious Travel to Titan:** Before his suicide, Jerome tells Vincent, "I'm traveling too," suggesting that by giving Vincent his hair, a piece of himself will accompany Vincent on the journey to Titan, Saturn's fourteenth moon—a journey Jerome could never physically take.
* **The Final Gift of Identity:** This final offering is seen as Jerome's blessing and "the most precious farewell gift he has to offer: his identity". Jerome has secured Vincent's dream, and by ensuring his identity can continue, he completes his purpose and achieves a form of redemption.
* **Echoing an Earlier Scene:** The exchange is an inverted echo of an earlier scene where Vincent's love interest, Irene, gives him a lock of her hair for sequencing, so he can vet her genetic profile. While Vincent tosses Irene's hair away because he rejects the eugenics-driven social practice, he keeps Jerome's, signifying the value of their human bond over the value of the perfect DNA the hair contains.