Specialized chromosomes determine sex.
Nettie Stevens and Edmund Wilson explain how biological sex is determined by special chromosomes.
Hello, I'm Nettie Stevens. Dr. Edmund Wilson and I showed that sex is determined by special chromosomes. I did it by looking at cells of meal worms. [MEAL WORM LARVA] The following drawings are adapted from my 1905 paper. Body cells from female worms have 20 chromosomes, all similar in size. As expected, female gametes have a half set of chromosomes (10). [FEMALE BODY CELL GAMETE (EGG)] In male body cells, there are 19 similar chromosomes and one that is much smaller. I found that two types of male gametes are made during meiosis. Some sperm have the small chromosome, and some don't. [MALE BODY CELL GAMETES (SPERM)] I concluded that the "different" chromosome must be responsible for maleness in meal worms. This different chromosome Y and its larger partner X are sex chromosomes. Sex in most species is determined by these sex chromosomes. So, sex is inherited like a Mendelian trait. Human sex is determined this way... Females have two X chromosomes; Males have one X and one Y. Since females can only contribute an X chromosome, males are responsible for the sex of offspring. They can provide either an X chromosome for a female... XX: It's a girl! ....or a Y chromosome for a male. If meiosis and fertilization occur normally, there will be an equal number of males and females. XY: It's a boy!
sex chromosomes, x chromosomes,y chromosomes worm larva, edmund wilson, meal worms, male gametes, nettie stevens, fertilization, body cell, gamete
- ID: 16250
- Source: DNALC.DNAFTB
Nettie Maria Stevens independently developed the idea of sex determination by chromosomes.
Edmund Beecher Wilson independently developed the idea of sex determination by chromosomes.
DNAFTB Concept 9: Study of meiosis revealed the chromosomal basis of sex.
DNAFTB Problem 9: Try your hand at sex determination.
DNA is organized into 46 chromosomes including sex chromosomes, 3D animation
Theodor Boveri described the process of meiosis. He also showed that although chromosomes may look similar, they have specific hereditary qualities.
"Fig. 6. The chromosomes of man"
DNAFTB Animation 8: Theodor Boveri presents chromosomes' role in development.
The Y chromosome.
Offspring arise from the union of specialized sex cells â a female egg and a male sperm.