Nettie Stevens
“ A Battle of the Sexes ”
By 1900 it was already well known that an offspring inherits equal numbers of chromosomes from each of its parents . What part , if any , chromosomes played in heredity was still unproven . In fact , it was still not known how the sex of an offspring was determined . Most scientists believed that sex was determined by external factors acting on the fertilized egg , such as temperature and nutrition .
Nettie Maria Stevens was born on July 7 , 1861 in Cavendish , Vermont , USA . She attended private school at Westford Academy and went on to teachers ’ college before settling on a position at a high school in Lebanon , New Hampshire .
Nettie worked in various teaching positions until 1896 , when at the age of 35 , she went to Stanford University , and earned a Master ’ s degree in Physiology . There , she specialized in studying histology and cytology .
In 1901 , Nettie moved to Philadelphia where she began working towards a doctorate in cytology . The head of biology was Thomas Hunt Morgan . Her doctorate took her to Germany where she worked with Theodor Boveri , who , like Morgan , was also working on the role of chromosomes in heredity .
In 1905 , Nettie discovered two different types of chromosomes ( large and small ) in the sperm of male mealworm beetles . She went on to identify these as the X and Y chromosomes and deduced that an organism ’ s sex is determined by a specific pairing of male and female chromosomes ( males have XY and females XX ).
Coincidentally , Edmund Beecher Wilson , America ’ s first cell biologist , independently made the same discovery as Stevens , also in 1905 .
Many scientists were skeptical at first and did not believe the evidence , including Morgan , who was nevertheless credited for most of Stevens ’ s and Wilson ’ s discoveries . Morgan went on to win the Nobel Prize in 1933 for his discoveries concerning the role played by the chromosome in heredity .
Nettie Stevens died , at age 50 , of breast cancer on May 4 , 1912 .