Gen. Biology...NEED HELP ASAP

  1. My final exam for general biology is in 3 hours and I still have one question that I can't seem to answer on my review. I have to pass the final to get credit for the class. The question is...

    "What is an example of evolution using genetics?"
    To which I answered,
    "A large number of houseflies died after the introduction of DDT; most houseflies born today have a resistance to DDT."
    For reference, DDT is the chemical in bug spray that kills bugs.

    My instructor has already told me via E-Mail that my answer is right but he wants me to show genotypes. I totally sucked at the chapter with genotypes and phenotypes. Can someone help?

    Thanks!
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  2. 14 Comments

  3. by   SuesquatchRN
  4. by   JaredCNA
    Thanks for the site. It's a good reference.

    Now that I understand genotype more, I'm still having a hard time "showing the genotype." I don't know if that is like...

    XXDD = male resistant to DDT
    XYDD = female resistant to DDT

    XXDD x XYDD

    And then do the punnet square or whatever. I asked him for help on that part and he said he can't help me. No one in my class is available right now.
  5. by   SuesquatchRN
    I don't know what he means by "showing the genotype."

    Is the Punnett square the Mendelian square?
  6. by   SuesquatchRN
    Okay, I did a little poking around via Google and these types of questions want the Punnett square shown.
  7. by   JaredCNA
    I don't think we covered Mendelian Squares, so I guess he's looking for a punnet square.

    Ack, so lost. How would I cross maternal and paternal if I don't know if they carry the DDT-resistance gene, if they don't carry it, etc.?
  8. by   SuesquatchRN
    Quote from JaredCNA
    I don't think we covered Mendelian Squares, so I guess he's looking for a punnet square.

    Ack, so lost. How would I cross maternal and paternal if I don't know if they carry the DDT-resistance gene, if they don't carry it, etc.?
    Well, at least one of them has to carry it if it's a dominant trait, both if it's recessive. Right?
  9. by   SuesquatchRN
    The Punnett square is what I call the Mendelian square, Jared.
  10. by   JaredCNA

    DD x dd

    D D

    d Dd Dd

    d Dd Dd

    Maybe? But I still don't know if the gene is dominant or recessive in mother or father.
  11. by   SuesquatchRN
    You have to make it up, Jared.
  12. by   JaredCNA
    Well, does the monohybrid cross above look alright to you? The father has the dominant gene.

    Thanks so much for the help.
  13. by   SuesquatchRN
    The one on the preceding page? Yes.
  14. by   JaredCNA
    Whew, much easier than I thought.

    Thanks again.

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