Fruit fly studies Drosophila melanogaster

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Fruit fly studies Drosophila melanogaster

• Culturing techniques and important control issues

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Terms to know.

• Homozygous
• Heterozygous
• Dominant
• Recessive
• Parental generations
• Filial generations
• Punnett square
• ratios

• Alleles
• Traits
• Gene combinations
• Gametes
• Sex linked traits
• Genotype
• Phenotype

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Sex linkage shown with flies first

• Normally, fruit flies always have RED eyes, but
  Morgan saw a white eyed one show up, and it was
  MALE!! Thought that this was strange, so he
  conducted an experiment (TESTCROSS)
• P white eyed X red eyed
• F1 all red eyed offspring
• (thus concluded that red is
  dominant over white for color)
• F1 red eyed X
  red eyed
• F2 ¾ red eyed ¼ white eyed
• AND ALL OF THE WHITE EYED ONES WERE MALE!!!
• Determined that this was a sex-linked trait the
  trait for eye color in fruit flies is carried on
  the sex chromosome.

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Reasons to use fruit flies for study

• produce about 100 offspring per egg lay good
  statistics!
• Mature in only 15-20 days
• Only have 8 chromosomes (4 pair) so less to look
  at
• Chromosomes are VERY large and easy to see and
  locate
• Easy/inexpensive to raise
• Sexes are easily distinguished
• --female is larger
• --shapes/colors of abdomen identify sexes at a
• glance
• (male abdomen more rounded, black
  tipped)
• --males have sex combs on front legs

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• Flies will be shipped in capped vials with foam
  plugs
• Optimal temp is 20-21 oC
• Equipment needed
• culture vessels
• plugs
• medium (feeding material) instant (flakes,
  water, yeast)
• marking pencils
• anesthetic (Fly nap)
• white cards for examining flies
• paint brush
• dissecting scope

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Life cycle

• 4 stages
• egg, larva, pupa, adult (goes through
  metamorphosis)
• Two weeks time
• 8 days in egg and larval stages
• 6 days in pupal stage
• Day after eggs laid, larva hatches maggot
• Larva molts twice before and after molting,
  called an instar (fruit fly has 3 instars)
• 2 days after emerging, female can start laying
  eggs uses sperm from first mating for entire
  time is fertile!

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Anesthetizing

• FlyNap see page 9 of booklet
• chemical works for about 30-45 minutes
• be sure to NOT get the chemical on the plug!
• lay vials on sides when anesthetizing (if doing
  in a vial with food present) FLIES WILL FALL
  INTO FEEDING MEDIUM AND DIE!

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Sexing

• Use white card and sorting brush DONT touch
  the flies directly!
• Look for DARK, rounded abdomens in males
• Look for lighter, pointed abdomens in females
• Also, males have sex combs on front legs see
  page 12 in booklet

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Mating and Counting

• Label vials clearly with dates hatched, dates
  placed together, and characteristics of parents
• Parental generation vs. filial generations
• See pages 15-17 for descriptions and diagrams of
  characteristics