Nettie’s most notable research was
on mealworms. She studied other insects as well, but let’s focus on the
mealworms. She was studying their chromosomes, and she noticed something
strange. The female mealworms had a pair of X chromosomes, while the males had
a set of XY chromosomes. The Y chromosomes was named so because when Nettie saw
the Y chromosome, it appeared as though it was a piece of an X chromosome was
cut off, leaving a Y shape. This was the first official discovery of sex
chromosomes. Before Nettie, scientists didn’t understand how sex was
determined. People thought that the sex of the fetus was determined by the
pregnant woman’s body temperature (warmer temperatures were said to produce
males) and what the woman ate. Scientists had guessed that something else
controlled sex, but they couldn’t figure out what. Nettie provided solid
evidence that sex was determined by these special chromosomes. She published
her work, but was met with criticism. At the same time, Edmund Wilson was also
working on the discovery of sex chromosomes. Although Nettie’s research was
better supported, she is often overlooked. Nettie died of breast cancer just
seven years after she published her work, and she never got to see the impact
she made on genetics. Fortunately, she is now starting to get the recognition
she deserves.
All right, so sex chromosomes were
discovered, now what? What came out of this new information? Thomas Hunt
Morgan’s research on Drosophila
melanogaster was made possible by Nettie’s findings. Mendelian and chromosomal theories of inheritance were further
supported with Nettie’s research. A few years down the line, the SRY gene was
identified. This is the gene that controls typical male trait expressions. If
SRY is expressed, you are determined as a male. No SRY gene, you grow to be a
female. We gained a better understanding of sex linked traits and diseases. We
found that XX/XY sex chromosomes were not the only systems. Lizard males, for
example, have ZZ chromosomes. Scientists are beginning to understand that sex
determination in humans isn’t as binary as we think it is. Nettie was an
incredible scientist, who worked hard for her education, who was at the top of
her classes, and who loved research with all her heart. She helped pave the way
for the future of genetics.
Sources
“Women in Science: 50 Fearless Pioneers Who Changed the World,” written and illustrated by Rachel Ignotofsky.
Clarra-
ReplyDeleteI had never heard of Nettie Stevens before reading your post! I think it was a great choice for you to discuss this influential woman in science. Sex chromosomes are truly a fascinating topic; especially because they differ so much between species. Y chromosomes are particularly interesting because they are not known to provide much information. In my undergrad genetics course I learned that the size of the Y chromosome has decreased evolutionarily overtime to prevent mutations, but the it is critical in male development due to the SRY region. It makes me wonder what additional information is present on the Y chromosome (discovered or not) and how it plays a role in gender differences; and, if human males will change genetically if the Y chromosome continues to decrease in size overtime.
Hey Clarra,
ReplyDeleteI can't believe that people thought that the gender of a baby could be determined by the body temperature of the mother, like turtles or crocodiles. I'm glad that you are introducing me to many other female scientists who I would have probably never heard of unless I read your post. Her groundwork in sex chromosomes is greatly appreciated because now we can have the knowledge to know that there are X and Y chromosomes and there is a difference for males and females for gene expression. My question for you is, what are some examples of sex-linked disease?
Some sex-linked diseases include Fragile X syndrome, Hunter syndrome, Adrenoleukodystrophy (ALD), and Rett syndrome. Fragile X syndrome causes mental retardation in males. Hunter syndrome causes deformed facial features in infants. This disease is especially tricky because the first symptoms are common colds and ear infections, something every child experiences. ALD is the result of the body not being able to break down fats. The fats build up in the brain, causing seizures and other physical problems. In Rett syndrome, gray matter in the brain is disrupted, leading to the development of small heads, hands, and feet. This disease is mostly prominent in females. All of these diseases mainly affect the X chromosome, whether it be the dominant or recessive X chromosome.
DeleteThere are very few diseases linked to the Y chromosome because it contains very few genes. On top of sex-linked diseases, sometimes there’s an issue with the sex chromosome number. These diseases include Turner’s syndrome where a female only has one X chromosome, Klinefelter syndrome where males express more than one X chromosome, and Triple X syndrome where females express XXX, and XXY syndrome.
Sources
Sex Linked Diseases: https://en.wikipedia.org/wiki/Sex_linkage
Sex Chromosome Abnormalities: http://anthro.palomar.edu/abnormal/abnormal_5.htm
It makes me sad that I have never heard of her before now and that she died before her work became known and appreciated. Thank you for giving her some attention. It makes me wonder how many other female scientists made remarkable discoveries but were over shadowed by the work of men.
ReplyDeleteJust like those who have commented before me, I have never heard of her! It's always encouraging to hear about successful women in the sciences and I am glad she is getting her recognition. I wonder if how people used to think temperature determined the sex of your baby and what they ate is how the old wives tails began. I have heard a few before, such as what you crave, if you have morning sickness or not, or if you are carrying the baby high or low. Maybe these were ways that people used to predict the sex of the baby before her discovery, and people still use them today.
ReplyDeleteWhat interests me about females having a X,X genotype is x-inactivation, where one of the female X chromosomes gets silenced randomly. Calico cats are a great example because the cause of their coloration is due to this random x-inactivation. Furthermore, X-linked diseases can be corrected in females if the other X has a "non-disease" gene.
ReplyDeletehttps://en.wikipedia.org/wiki/X-inactivation
It was almost lucky that the first work on sex determination took place in insects that have similar systems to our own. There's tons of variation in the relationship between chromosomes and sex determination among eukarya.
ReplyDelete