Nettie Stevens The GENETICS PIONEER who discovered what makes animals male or female
Chromosome Cell
Late starter Born in Vermont, USA, in 1861, Nettie Stevens worked as a teacher before becoming a scientist in her thirties. At the time, nobody understood what made an animal male or female. Stevens began RESEARCHING CHROMOSOMES, the thread-like structures made of DNA inside a cell’s nucleus. A cell’s chromo nucleus con tains somes.
w she chan Ho ge d… Steve ns s my
puzzle stery tha olved a t d that ascientists had long deter n anim by pro ving min al’s not e ed by gen sex is xtern al fac etics and tors.
the world
X and Y
38
By studying mealworms, Stevens found that males produce sperm containing either X OR Y CHROMOSOMES, while females produce eggs with only X chromosomes. If an egg is fertilized by a sperm with the Y chromosome, a male offspring is created. If the sperm has an X chromosome, then the offspring is female.
