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N. M. Stevens

(Stevens, N. M. (Nettie Maria), 1861-1912)

Nettie Stevens. Black-and-white photograph, 35.5 x 28 cm Restoration notes: Little dust spots everywhere! I've done my best to remove them. Some fading to bottom of oval image, likely from handling; used a very light burn on there. Lots of small patches of staining, both light and dark; that was a pain to fix. It's grainy, but not much you can do about that; that's just cameras at the time.
Image from Wikimedia Commons

Nettie Maria Stevens (July 7, 1861 – May 4, 1912) was an American geneticist who discovered sex chromosomes. In 1905, soon after the rediscovery of Mendel's paper on genetics in 1900, she observed that male mealworms produced two kinds of sperm, one with a large chromosome and one with a small chromosome. When the sperm with the large chromosome fertilized eggs, they produced female offspring, and when the sperm with the small chromosome fertilized eggs, they produced male offspring. The pair of sex chromosomes that she studied later became known as the X and Y chromosomes. (From Wikipedia)

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