Genetics and evolution,
hand in hand!
A set of lab exercises with fruit flies!
Evolution Lab Exercise: Continued
“Natural selection”
• Some gene types will spread more than others
because helps the animal live or helps them
have more babies (“survival of the fittest”)
• In 1859, Charles Darwin wrote that this
happens a lot
– Could explain giraffe’s neck
– Could explain differences in bird
beak shapes
We studied natural selection in
fruit flies
• Used ~4 white-eyed males
and 1 red-eyed male (1/5)
• If no evolution, then 1/5of
daughters should have redeyes
• If having “red eyes” helps
the dad have more kids,
what did we expect to
happen over time?
Collecting Data
• Anaesthetize flies with “Fly Nap”
• Keep vial of flies on its side
and DO NOT shake the vials.
• Wait until all of the flies are completely
motionless.
Step 3b: Collecting Data
• Pour out sleeping flies onto
white piece of paper
– They won’t wake up
• Sort by sex first
• Sort by eye color next
• White male, white female
Red male, red female
Step 3c: Collecting Data
• Sort into these four piles
• Count the number of flies in
each pile
What did you see?
• Among sons?
• Among daughters?
• In “control” groups (where there was no redeyed male)?
Step 4: Results and Conclusions
• Was your hypothesis correct?
• What can you conclude from your results?
We witnessed evolution by natural
selection!!!
• Among the daughters, more than 1/11 have
red eyes.
– Male with red eyes passed on his red eye gene
way more than did males with white eyes.
– Why was he more successful?
– -Why no red eye sons?
What makes boys vs. girls?
• Boys & men have a gene on something called
the “Y” that makes them turn male
• Girls & women don’t have this- have 2 “X”s
instead.
XX
XY
What makes boys vs. girls?
• Mom always gives an X (all she’s got),
but
– If get the X from dad, turn into girl
– If get the Y from dad, turn into boy
Why no red-eyed sons?
MOM
DAD
Red eye color gene is
on dad’s X chromosome,
so SONS never get it!
End of Evolution Lab Exercise