1. Sex-Linkage (X-Linked Traits)
Drosophila melanogaster

2. Thomas Hunt Morgan – (the father of modern genetics)
He found genes located on the X chromosome that regulate fruit fly eye color.
Genes on the X
chromosome are
said to be X-linked

3. Thomas Hunt Morgan was studying evolution and was looking for mutations in fruit flies (Drosophila).
Morgan and his “F1s”
(His two daughters)

4. Morgan noticed that while most fruit flies had red eyes, there were a few white-eyed fruit flies.
He also noticed that ones that had white eyes were all males.

5. Morgan’s Experiment:
1) Morgan crossed a true-breeding, red-eyed female with a white-eyed male, he got all red-eyed flies in the F1 generation.

6. WHY? 2) When he crossed two F1 red-eyed flies,
he got three red-eyed flies to every one
white-eyed fly. ALSO-the white-eyed flies
were male.
WHY?

7. As stated by Morgan the gene for eye color is located on the X chromosome.
R = red color r = …white complelely color dominant over the…

12. more often than females
Male fruit flies
have white eyes
more often than females
Because females get a second chance at a dominant gene, they’re usually red-eyed.
Males only get one chance at a dominant.
Males are more likely to express recessive traits if the gene is on the X chromosome. (hemophilia, color-blindness, muscular dystrophy.)

13. Other interesting Drosophila variations: