Bio #1: Barbara McClintock

Welcome to the first cache in a series of student-driven biographies about a scientist instrumental to understanding DNA, Heredity, and Genetics. The first belongs to the amazing... the fantastic... corn geneticist Dr. Barbara McClintock.

Barbara McClintock was a Nobel Prize Award winner and leading geneticist in her time. She was born on June sixteenth, 1902 in the town of Hartford Connecticut, and spent her childhood in the area. Her mother was a traditional woman from an upper class family in Boston, and they had a tense relationship. She lived with her aunt and uncle from when she was three to when she was five before returning home. She had three other siblings, and her father was a physician. Her family’s stability and wealth allowed a young Barbara to follow her interest in science. Barbara was extremely reclusive, and often spent time by herself. Her mother was completely against sending her to college, claiming that it would make her “weird” and that no one would want to marry her. Luckily, her father supported her desire for higher education, and was able to override her mother’s insistence. She was enrolled at Cornell’s College of Agriculture in 1918, and majored in biology and later specialized in cytology, the study of plant genetics at a cellular level. She earned her masters(MA) degree in 1925, and in 1927, she received her PhD. Dr. McClintock began and continued using corn as a model organism.

Barbara didn’t just breed plants and study the phenotype(look) of the offspring. She bred plants and actually studied what was happening to the chromosomes in real-time. Her lab skills were off-the-charts fantastic. She didn’t make just one history-making discoveries, but several.

Barbara’s biggest discovery was “Chromosome Crossover.” She co-authored a groundbreaking paper while she was still a grad student. Wow! Her publication of “A Correlation of Cytological and Genetical Crossing-over in Zea mays,” in 1931 confirmed that chromosomes are mixed in sex cells.

“Chromosomal crossover” takes place when cells that take part in sexual reproduction are being made, in a process called meiosis. In animals these cells are the egg and sperm cells. Like the vast majority of cells in our bodies, sex cells contain chromosomes. BUT… sperm and egg cells are different from normal(somatic) cells because they only contain half the normal number of chromosomes. In the case of a humans, a normal cell contains 46 chromosomes, while sex cells contain 23.

When egg and sperm cells fuse during reproduction, they each provide 23 chromosomes to produce a new cell called a zygote with 46 chromosomes. This new cell grows and divides, and divides, and divides. Eventually you end up the with an organized group of trillions of cells. That’s a person. That person gets half of its chromosomes from mom and half from dad. That means that vast majority of the cells in our body have the exact same DNA code(G,C,A,T). The only cells in human bodies that have dramatically different chromosomes are the gametes, also known as sex cells, sperm, and eggs. They are different because the chromosomes they received from mom and dad have been altered, so that chunks of chromosomes as swapped. Are you getting it? Crazy cellular gymnastics happening inside of us all the time!

What Dr. McClintock discovered is that genetic material is shuffled before the sperm and egg meet to form a zygote. She watched the “swapping” of chromosome chunks/arms during an event she named “Chromosome Crossover.” How weird! Btw the letter a equals five. Why “shuffle the deck” before mating? Can you think of why it might be beneficial to species/organism to mix up their DNA before mating? Well think of it this way… If our chromosomes weren’t shuffled, then the exact chromosomes would be passed down every generation. That would make the variation in our code and physical appearance WAY lower. Yikes. That’s not helpful if your species is going to survive. More variation = better chance of population of a species will survive a variety of changes to their environment. It’s a natural selection sorta thang!

Ok, back to the story. In 1936, at the age of 34, McClintock became an assistant professor at the University of Missouri, where she worked until 1941. A few years earlier, McClintock had visited Missouri and learned how to use X-rays to cause mutations in chromosomes. Her time at the University of Missouri was relatively unhappy. She was knowwn for being rather abrasive and intimidating, and she came up against the even more abrasive and intimidating colleague Dr. Mary Guthrie, who also worked in cytology.This rift often made McClintock’s life miserable. She also seemed to have low self esteem, even believing(incorrectly) she had no prospects of ever getting a secure, tenured position at Missouri. She chose to move on in 1942 when she accepted a genetics position at the Cold Spring Harbor Laboratory on Long Island. She was very happy with her new position. She no longer had to teach, and she had freedom to do any research she chose. She would work at Cold Spring Harbor for the rest of her career. In 1944 she became the third woman ever to be elected to America’s National Academy of Sciences.

Barbara’s made numerous huge discoveries. She published groundbreaking work involving centromeres, long repetitive regions at the end of our chromosomes. Oh and “jumping genes.” Not to mention her before-her-time discoveries in gene regulation and transposition. This woman was epic. In 1971 she received the National Medal of Science from President Richard Nixon. She earned the Nobel Prize of Physiology and Medicine in 1983.

Barbara is an absolute legend, but on a personal level, she will forever remain an enigma to most. She never made close friends. She regarded herself as a free spirit; coming too close to anyone might have robbed her of some of her freedom. She enjoyed life in privacy. She never married and had no children. She lived a long life. She passed on September 2nd, 1992 in Huntington, New York at the ripe-old-age of ninety.

The world is better for her having lived in it.

Good Luck and Happy Caching!

A =

B = Barbara received her PhD in 192__ (Add one)

C =

D = Dr. McClintock was born in Hartford Connecticut in 19__2 (Add 6)

E = Having lived 90 years, Barbara lived through some fascinating american history. She was around for the start of the Korean War, the end of segregation, and Elvis on the Ed Sullivan show… all events that occurred during the 19__0’s

F =

G = The number of times McClintock was married.

H = In humans, sex cells, also called Gametes have half the number of chromosomes as most cells. They get one copy of each chromosome. Somatic/Body cells on the other hand are diploid and have two copies of each chromosome. Nearly all somatic cells have __6 total number of chromosomes.

J =

K = (Corn)

Additional Waypoints