RT @Ancestry: Happy 155th birthday, Nettie Stevens, who discovered X and Y chromosomes determine gender: http://ift.tt/2tpPRmb https://t.co/4oIZ3qG0Nd

Happy 155th birthday, Nettie Stevens, who discovered X and Y chromosomes determine gender: https://t.co/MJjmSx7mM1 #History http://pic.twitter.com/LFm8LUVoxr

— Ancestry (@Ancestry) July 7, 2017

from Twitter https://twitter.com/deabigt

July 07, 2017 at 10:55AM
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