The Fly Room

Who would have the thought the most important molecules in our bodies would be helical works of art. There is no molecule in our bodies more important to explaining who we are. DNA is a simple code made of only 4 coding molecules, Guanine(G), Cytosine(C), Adenine(A), and Thymine(T). These pieces of code face inward, held in place by a backbone made of phosphates linked together. Although there are only four pieces of the code, the length of the code is comparatively massive. For instance, chromosome one is over 250 million GCATs long and contains nearly 3,000 genes. The DNA from these genes escape the nucleus of our cells by being copied into RNA, which is used as a code to make a specific protein essential to making a human. The code goes DNA -- > RNA → Protein.

We take our DNA for granted. Less than a hundred years ago, we didn't even understand its function. If a scientist had been asked what a gene was made of, how it accomplished its function, or where it resided within the cell, there would have been very few satisfactory answers. The role of DNA in defining heredity, biology, and chemistry cannot be overstated. It tells us so much about who we are.

Let's travel back in time… then speed through time quickly until we stop in the 1920s. Flash back to Gregor Mendel working in the garden of a monastery in the 1860s, silently discovering that traits/genes are passed down from parents in pairs, one from the mother and one from the father. Mendel confirmed his results by analyzing the traits of pea plants after mating purebred and hybrid parents. The pattern of resulting traits left little doubt that there were "two genes" inherited, one from each parent. Sadly his work was published in an obscure German journal and was ignored by his peers.

It would be over three decades before Gregor Mendel's work was re-discovered. At this time scientists did not understand "what" was being passed on from parent to offspring. DNA was first discovered in 1869 by Swiss physician Friedrich Miescher. He had no idea what its function was. The three main parts of DNA(sugar, phosphate, base) were identified in 1917 by Phoebus Levene. At this point scientists had not discovered the connection between DNA and genes. Scientist knew "genes" existed, but didn't know their physical form. In fact it was not DNA that was predicted to be the molecule of inheritance, but rather PROTEINs.

After three scientists uncovered Mendel's work in 1900, the discovery sparked many scientists to seek the physical form of a "gene." Several scientists made contributions to the cause. German scientist Theodor Boveri's work in sea urchins suggested that "string-like" chromosomes are where genes reside. This hypothesis was again proposed by one-time Kansas farm boy Walter Sutton. He moved to New york to study grasshopper gametes and reproduction. Furthermore, the pioneering work Nettie stevens had shown that beetles have different sized chromosomes that determine their gender.

All of this work led up to the discoveries of our protagonist Thomas Hunt Morgan. Thomas was born into a wealthy family Kentucky family. Thomas went to the University of Kentucky, graduating as the valedictorian in 1886. He went on to get his PhD at Johns Hopkins in Baltimore Maryland in 1890. After graduating, he went on to become a professor at Bryn Mawr just west of Philadelphia. He studied embryology in sea urchins, worms, and frogs.

Just like many other scientists around the world, the rediscovery of Mendel's experiments inspired Thomas to search for the material that makes up genes. Morgan had resisted Mendel's theory of heredity at first, arguing that it was unlikely that complex information "could be stored in discrete units in the cell. He was soon convinced by William Bateson and others whose experiments confirmed and further proved Mendel's theory. In 1904 he was invited to do his research at Columbia University in New York. At this point his primary focus was to prove once and for all what physical form a gene takes. Dr. Morgan wanted to answer a number of question. For instance, how were genes organized on chromosomes? Were they strung along chromosomal filaments like pearls on a string? Did every gene have a unique location on a chromosome? Did genes overlap?

How do you answer questions like these? Thomas Hunt Morgan began by finding a new model organism. He chose the humble fruit fly. He started breeding flies around 1905 in milk bottles filled with rotting fruit in his lab at Columbia University. His lab was famously referred to by its students as the "Fly Room." It was a strange work environment. Overripe bananas were hung from sticks around the lab and the smell was overpowering. J = 5 As Morgan moved throughout the lab, a haze of escaped flies buzzed and moved around him.

Just like Mendel, Morgan began by identifying heritable traits like eye color, wing shape, and body abnormalities. Mendel did the same thing with the traits of seed and flowers using pea plants back in the 1860s. Morgan and his students could track the inheritance of traits across multiple generations. Many of Morgan's crosses resulted in the exact same ratios predicted by Mendelian genetics, but not all of them. Between 1910 and 1912, Morgan conducted thousands of crosses between purebred mutant and normal flies. He found a few surprising patterns. Some genes seemed to act like they were "linked" to each other.

For example, a mutation in the gene white eyed makes the eyes of a normally red-eyed fly completely white. The white eyed flies were crossed with normal flies and the resulting offspring were a predictable 3:1 ratio of red to white eyes. Red eyes are dominant over white eyes in the same ratio Mendel would have predicted. Thomas made another astounding observation, that the white eyed flies were all male, meaning that the gene must be in a specific location on the Y chromosome.

Dr. Morgan and his students performed many crosses. In one such cross, the gene for brown colored flies was linked to the mutant trait for wing shape. They proved that these two genes always occurred together because they were close together on the same chromosome. He was the first to determine that genes have a specific location in the same order on chromosomes, like pearls on a necklace. Morgan had discovered an important modification to Mendel's laws. Genes did not travel separately if they are linked on the same chromosome.

No longer was a gene a "purely theoretical unit." It was a material thing that lived in a particular location on a chromosome. The fly room was no one-trick-pony. Not long after this breakthrough, they noticed that some of their linked genes would on rare occasions separate during a cross. What he had stumbled upon was the phenomenon he named "Crossing over." During the production of gametes(meiosis), the paired chromosomes of a fly are swapped once along the chromosome. Some genes were so closely linked that they never separated. Morgan hypothesized that these were closest together on a chromosome. Other linked genes split more frequently, suggesting they were further apart. The lab realized that they could use the likelihood of crossing over to map the location of genes on a chromosome. They started making a map of the distance between genes on each chromosome.

Between 1905 and 1925 the Fly Room at Columbia was the center of the genetics world. The chain reaction of enormous discoveries from one lab are very rare in the history of science. Over the next decades, a number of Nobel Prizes would be showered on the occupants of the Fly Room. In the end it wasn't just Dr. Morgan, but his students, and his student's students received nobel prizes. In 1928 Morgan took a position as a professor at Caltech in Pasadena California. He continued to work there until his retirement in 1942. He died in 1945 of a heart attack at the age of 79.

NAB CD.EFG W10H JK.LMN

A = In Thomas Hunt Morgan's famous experiment he crossed white eyed male flies with red eyed females. The eyes of their offspring were were a ____ to one ratio of red to white eyes, just as Mendel would have predicted.

B = DNA was first discovered in 186___

C = Dr. Morgan began breeding flies in 190___

D = The three main components of DNA, Sugar, Phosphate, and Bases were identified in 191____

E =

F =

G = Thomas graduated from the University of Kentucky in 188__

H = The number of bases in the DNA code.

J =

K = A chromosome with almost 250 million base pairs.

L = Dr. Morgan began his work at Columbia University in 190__

M = Thomas lived to the age of 7__

N =

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