Thomas Hunt Morgan | Father of Experimental Genetics

 Thomas Hunt Morgan

Thomas Hunt Morgan

Thomas Hunt Morgan proves the theory of chromosomes experimentally. He is also known as the father of experimental genetics. He used a very strange creature for his experiment. This strange creature is a fruit fly.

Now, why the fruit fly is a strange creature?

Fruit flies or drosophila melanogaster have chromosomes that are about 60% similar to human chromosomes. This fruit fly is used as a model organism in the field of genetics. This fruit fly is also used for the study of most neurodegenerative disorders.

The most special thing about this creature is its mutant form. 

A normal fruit fly has the characters like red eyes while the mutant fruit fly has white eyes.

One day, Morgan found this mutant fruit fly. He was shocked after seeing a fruit fly with white eyes.

This strange fruit fly motivates Morgan to know something new about genetics. Morgan observed that the white-eyed fruit fly is the male organism only.

He has done experiments on this fruit fly as Mendel did once in the past on pea plants and Morgan’s experiments then proved the chromosomal theory of inheritance and Mendel’s work.

Experiment.

• Morgan takes a mutant fruit fly, which is a male organism and has white eyes.
• He crossed this male fruit fly with a red-eyed fruit fly which was a female organism.
• In the F1 generation, he got red-eyed fruit flies.
• These red-eyed fruit flies in the F1 generation show that red-eyed eyes are a dominant character in fruit flies.
• Then he crosses the members of the F1 generation.
• He got some white-eyed fruit flies and many of the red eye colored fruit flies.
• The interesting thing in this experiment is that he got the same ratio as Mendel got in the past. The only difference between his and Mendel’s experiment is that Mendel used the pea plant and he used fruit fly.
• But this is not as simple as Mendel does. The only male fruit fly has white eyes, and every female fruit fly has red eyes.

Now, why did only males get white eyes?

Morgan observed this mutant fruit fly very closely and found a new thing and that thing is linked characters. He observed sex-linked genes.

What is meant by sex-linked?

The simple meaning of this term is that some traits are sex specialized. 

This means in the case of the fruit fly, only the male fruit fly was getting white eyes which means the white eye is a sex link trait that is seen only in male fruit flies.

• Morgan explained the linked characters very well.
• According to him, the white eye color character is present on the X chromosomes of males, if we have a female with chromosomal pair XX and a male with chromosomal pair XY.
• According to Morgan, the white eye color is sex-linked with male organisms. So, we can show the white color eye with W. Here, W is an allele and is linked to the X chromosome.

We can make the cross of both male and female chromosomes. We got all red-colored eye fruit flies in the F1 generation.

If we cross the members of the F1 generation then we got a white color eye male fruit fly.

White eye color is a recessive trait, so it is only seen in male fruit flies and not seen in female fruit flies because they have the alleles of the dominant red eye color.

We have another question here Why these linked characters are not observed by Mendel?

You can say that Mendel was lucky there because he choose only those seven characters which are not linked to each other in any way. 

Conclusion.

1. Morgan concluded from his experiment that genes are present on chromosomes.
2. Genes decide the characters of the next generation.
3. Genes have dominant as well as recessive traits that we call alleles.
4. Some characters are interlinked with each other.
5. He proved the linked characters through his experiment on the fruit fly.
6. He also proved experimentally the theory of chromosomal inheritance and Mendel’s work.

 

Now how can these observations relate to the chromosomal theory of inheritance and Mendel’s work?

Firstly, we compare Mendel’s work and Morgan’s work:

• Mendel works on garden peas which a plant, while Morgan works on fruit fly that is an animals.
• The phenotypic and genotypic ratios are very nearly the same in both Mendel’s and Morgan’s experiments.
• Mendel discovered the alleles which he called factors while Morgan introduced the term linked characters in the field of genetics.
• Both Mendel and Morgan are the best in their work but Morgan got appreciation and popularity while Mendel’s work was rejected in his life.
• We can say Mendel is the father of genetics and Morgan is the father of experimental genetics.

 

Now have a look at the chromosomal theory of inheritance and Morgan’s work.

The chromosomal theory of inheritance also accepts Mendel’s work but this theory mainly concentrates on chromosomes and the transmission of characters from one generation to another.

Morgan’s work satisfies this theory and the theory of chromosomes was accepted after Morgan’s experiment.