Today In Science History – September 25 – Thomas Hunt Morgan and Chromosomes

Thomas Hunt Morgan
Thomas Hunt Morgan (1866-1945) in 1891. 1933 Nobel Prize in Medicine for finding the role of chromosomes in heredity. Credit: NIH

September 25 is Thomas Hunt Morgan’s birthday. Morgan was the American zoologist who was the first to link hereditary traits to chromosomes.

Morgan completed much of his work using an experimental model subject familiar to many first-year genetics students, the Drosophila fruit fly. During one investigation, he noticed one of his male fruit flies had white eyes instead of the more common red of wild Drosophila. He decided to test if he could breed the white eye trait into a new generation of flies. He placed his white eyed fly in a container with several red eyed females. The resulting children all had red eyes. He then tested to see if this trait was recessive by breeding the children of the white eyed father together. The second generation had several white eyed progenies at a ratio of one white eyed to three red eyed. He also noticed all the white eyed flies were male. According to the rules of inheritance accepted at the time, the ratio should have been 1:1 for male and female.

Morgan had heard of the research of E.B. Wilson and Nettie Stevens who showed sex determination was related to the accessory chromosome or X chromosome. Perhaps the X chromosome had something to do with the white eye trait for the Drosophila. He set up several different cross breeding trials while noting the chromosomes passed on from mother to progeny. Morgan found the white eyed trait seemed to follow the X chromosome through each generation. This discovery would be the beginning of modern genetics and earn Morgan the 1933 Nobel Prize in Medicine.

Fruit flies are commonly used to demonstrate or study effects in genetics, physiology, and evolution. They are short lived, easily cared for, breed easily and lay many eggs. They have a relatively smaller genome, with four pairs of chromosomes. There are one X/Y pair and three autosomes. Several genetic markers can be spotted such as curly wings, black or yellow body, and wings, white eyes, or stubble hair. The ease of care and identification make these insects extremely useful for students to get a hands-on taste of genetics.

Notable Science Events for September 25

1992 – NASA launches the Mars Observer

Mars Observer
Mars Observer. Jet Propulsion Laboratory

The Mars Observer spacecraft began its journey to Mars. The spacecraft was designed to study the topography, magnetic and gravitational fields, along with the climate and atmospheric circulation of Mars.

NASA lost communication with the Mars Observer satellite just three days prior to its insertion into Mars orbit. It is believed the most probable cause was a rupture in the fuel pressurization side of the spacecraft’s propulsion system. This would cause the fuel prematurely mix with the oxidizer and cause the satellite to spin out of control.

1986 – Nikolay Semyonov died.

Semyonov was a Russian chemist who shares the 1956 Nobel Prize in Chemistry with Cyril Norman Hinshelwood for their work in chemical kinetics. His work was in the area of chain reactions and combustion reactions.

1985 – William Cumming Rose died.

Rose was an American biochemist who discovered the amino acid threonine and its role in nutrition. He established ten amino acids: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine were all vital to human health.

1898 – Hieronymous Theodor Richter died.

Richter was a German chemist who co-discovered the element indium with Ferdinand Reich. They were investigating the presence of thallium in zinc ores using spectroscopy when Richter discovered a vivid indigo spectral line that identified a new element. They isolated this element and named it indium after the spectral line.

1866 – Thomas Hunt Morgan was born.