Thursday, September 25, 2014

ശാസ്ത്ര ചരിത്രം ഇന്ന് (സെപ്തംബര്‍ 25 )

September 25 is Thomas Hunt Morgan’s birthday.

Thomas Hunt Morgan (1866-1945) in 1891. 1933 Nobel Prize in Medicine for finding role of chromosomes in heredity. 
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 progeny at a ratio of one white eyed to three red eyed. He also noticed all the white eyed flies were male. According the 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 is 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.


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