Search results
Sex-limited inheritance in Drosophila. Science 32, 120–122 (1910) ( link to article) One day in 1910, Thomas Hunt Morgan peered through a hand lens at a male fruit fly, and he noticed it didn't ...
Transcript. Thomas Hunt Morgan's groundbreaking work with fruit flies in the early 1900s provided substantial evidence for the chromosome theory of inheritance. Morgan discovered a mutant white-eyed male fly and traced its inheritance pattern, revealing a connection between the X sex chromosome and the gene for eye color.
- 11 min
- Sal Khan
- This is a little bit of a confusing topic, so I hope I can help! First we need to remember that males are XY (X from mom, Y from dad) and females a...
- Yup! It's possible, but very unlikely as the female fly has to inherit Xw, the white eye allele, from BOTH parents, whereas for male flies, they on...
- He used a microscope to inspect his fruit flies in the early 1900's. Microscopes were invented in the 1600's. Giambattista Odierna originally descr...
- Do you mean Y-linked phenotypes? These are uncommon§ due to the small size of the Y chromosome, but do exist. For example, there is a strain of lab...
- Offspring: XwXw+, XwXw, Xw+Y, XwY 25% red-eyed female, 25% white eyed female, 25% red-eyed male, 25% white eyed male.
- It would help if you could give an example of a trait you heard. But such expression profiles are possible. Certain genes responsible for hairiness...
- it is possible
- Fruit flies are easy to anesthetize typically by filling the container with CO2.
- I'm pretty sure that's what would happen because the way it seems is that the Xw allele is similar to that for color blindness. So an Xw-Xw female...
- The white allele in an Xᵂ Y (male) fly is hemizygous, where did you hear otherwise?
May 22, 2017 · In 1910, Thomas Hunt Morgan performed an experiment at Columbia University, in New York City, New York, that helped identify the role chromosomes play in heredity. That year, Morgan was breeding Drosophila, or fruit flies. After observing thousands of fruit fly offspring with red eyes, he obtained one that had white eyes.
- Overview
- Key points:
- Introduction
- The chromosome theory of inheritance
- T. H. Morgan: Fun with fruit flies
- A "sex limited" inheritance pattern6
- X marks the spot
- Confirming the model
Thomas Hunt Morgan's experiments. The fruit fly (Drosophila melanogaster) as a model system.
•Boveri and Sutton's chromosome theory of inheritance states that genes are found at specific locations on chromosomes, and that the behavior of chromosomes during meiosis can explain Mendel’s laws of inheritance.
•Thomas Hunt Morgan, who studied fruit flies, provided the first strong confirmation of the chromosome theory.
•Morgan discovered a mutation that affected fly eye color. He observed that the mutation was inherited differently by male and female flies.
•Based on the inheritance pattern, Morgan concluded that the eye color gene must be located on the X chromosome.
Where are genes found in a cell? Odds are, you've already heard the punchline: genes lie on chromosomes. You may have even have heard the second punchline, the one that ushered in the modern genetic era: genes are stretches of DNA that specify proteins.
However, these were not always things that you could look up on Khan Academy! When Gregor Mendel began studying heredity in 1843, chromosomes had not yet been observed under a microscope. Only with better microscopes and techniques during the late 1800s could cell biologists begin to stain and observe subcellular structures, seeing what they did during cell divisions (mitosis and meiosis).
Who figured out that genes are on chromosomes? Walter Sutton and Theodor Boveri generally get credit for this insight. Sutton, who was American, studied chromosomes and meiosis in grasshoppers. Boveri, who was German, studied the same things in sea urchins.
In 1902 and 1903, Sutton and Boveri published independent papers proposing what we now call the chromosome theory of inheritance. This theory states that individual genes are found at specific locations on particular chromosomes, and that the behavior of chromosomes during meiosis can explain why genes are inherited according to Mendel’s laws2,3 .
Observations that support the chromosome theory of inheritance include4 :
•Chromosomes, like Mendel's genes, come in matched (homologous) pairs in an organism. For both genes and chromosomes, one member of the pair comes from the mother and one from the father.
[See diagram]
•The members of a homologous pair separate in meiosis, so each sperm or egg receives just one member. This process mirrors segregation of alleles into gametes in Mendel's law of segregation.
Morgan chose the fruit fly, Drosophila melanogaster, for his genetic studies. What fruit flies may lack in charisma (depending on your taste in insects), they make up for in practicality: they're cheap, easy, and fast to grow. You can raise hundreds of them in a little bottle with sugar sludge at the bottom, and many geneticists still do this today!
Morgan's crucial, chromosome theory-verifying experiments began when he found a mutation in a gene affecting fly eye color. This mutation made a fly's eyes white, rather than their normal red.
Unexpectedly, Morgan found that the eye color gene was inherited in different patterns by male and female flies6 . Male flies have an X and a Y chromosome (XY), while female flies have two X chromosomes (XX). It didn't take Morgan long to realize that the eye color gene was being inherited in the same pattern as the X chromosome.
This may have come as a surprise to Morgan, who had been a critic of the chromosome theory7 !
What made Morgan think that the eye color gene was on the X chromosome? Let's look at some of his data. The first white-eyed fly he found was male, and when this fly was crossed with normal, red-eyed female flies, the F1 offspring were all red-eyed∗ —telling Morgan that the white allele was recessive. So far, so good, no surprises there.
But when the F1 flies were crossed to each other, something strange happened: all of the female F2 flies were red-eyed, while about half of the male F2 flies were white-eyed. Clearly, the male and female flies were inheriting the trait in different patterns. In fact, they were inheriting it in the same pattern as a particular chromosome, the X.
Let's see how inheritance of the X chromosome can explain what Morgan saw. Earlier, we said that female flies have an XX genotype and male flies have an XY genotype. If we stick the eye color gene on the X chromosome (writing it as a little subscript, w+ for red and w for white), we can use a Punnett square to show Morgan's first cross:
Punnett square for mating of white-eyed male (XwY ) with red-eyed wild type female (Xw+Xw+ ).
Xw+Xw - red-eyed F1 females Xw+Y - white-eyed F1 males
_Image modified from "Drosophila melanogaster," by Madboy74 (CC0/public domain)._
The predictions match the F1 phenotypes, but this set of phenotypes could also be explained by a gene that is not on the X chromosome, since all the flies were red-eyed (regardless of sex). So the real test comes when the F1 flies are mated to make the F2 generation:
Morgan did lots of other experiments to confirm an X chromosome location for the eye color gene. He was careful to rule out alternative possibilities (for instance, that it was simply impossible to get a white-eyed female fruit fly)6 .
[See another of Morgan's experiments]
Pulling together all of his observations, Morgan concluded (correctly) that the gene must lie on, or be very tightly associated with, the X chromosome7,9 . A strong confirmation of this conclusion came later, from Morgan's student Calvin Bridges. Bridges showed that rare male or female flies with unexpected eye colors were produced through nondisjunction (failure to separate) of sex chromosomes during meiosis—basically, the exception that proved the rule10,11 .
Morgan also found mutations in other genes that were not inherited in a sex-specific pattern. We now know that genes are borne on both sex and non-sex chromosomes, in species from fruit flies to humans.
In 1910, American scientist Thomas Hunt Morgan performed a game-changing experiment. After breeding millions of fruit flies, Morgan identified a mutation in the white eyes of a fly.
Sep 25, 2017 · Thomas Hunt Morgan (1866-1945) On September 25, 1866 , American evolutionary biologist, geneticist, embryologist, and science author Thomas Hunt Morgan was born. He is famous for his experimental research with the fruit fly by which he established the chromosome theory of heredity. Thomas Hunt Morgan was awarded the Nobel Prize in Physiology or ...
People also ask
What were Thomas Hunt Morgan's experiments?
How did Thomas Hunt Morgan find a fruit fly?
What did Thomas Hunt Morgan discover?
How did Thomas Hunt Morgan discover chromosomes?
Thomas Hunt Morgan. Thomas Hunt Morgan (September 25, 1866 – December 4, 1945) [2] was an American evolutionary biologist, geneticist, embryologist, and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries elucidating the role that the chromosome plays in heredity.
