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Homework Help: Frequency and Location of Genes

  1. Nov 11, 2009 #1
    Hello. I'm currently studying for Biology and I'm looking over the quizzes we took in class to see what I need work on. So far, I have trouble on frequency and location of genes. Here's one of the questions I missed on the quiz (my answers are in bold):

    A man with the recessive traits of blonde hair and blue eyes marries an Asian woman whose family has no hint of either blonde hair or blue eyes.

    a) Provide genotypes for each, then give the gametes for each parent.
    Genotype - aabb
    Gametes - ab

    Genotype - AABB
    Gametes - AB

    Where A=dark hair; a=blonde hair; B=brown eyes; b=blue eyes

    b) All their (F1) children have dark hair and brown eyes. Give their gametes, assuming that hair color and eye assort independently.
    AB, Ab, aB, ab

    c) One of these F1 children marries an Icelandic person with blonde hair and blue eyes. They are prolific, producing 40 children! Of these, 18 have dark hair and brown eyes; 2 have dark hair and blue eyes; 17 are blue-eyed blondes; and 3 are brown-eyed blondes. What are the under-represented gametes of the F1 generation (i.e., the gametes of the F1 child-not the Icelander-that contribute to the enumerated children)? Why is their frequency so low?
    I only received points for answering Ab and aB as the under-represented gametes. Apparently, my reasoning was "inconsistent." I found the frequency of the under-represented to be 12.5%, which I'm not sure has to do with anything.

    d) Give all the information you can now infer about the location of the hair color gene and the eye color gene with reference to one another (hint: consider distance).
    I did not answer this one because I wasn't sure what it was asking for and I ran out of time.

    Thank you for your time :smile:
  2. jcsd
  3. Nov 15, 2009 #2


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    I have moved this to the Homework help forum.
  4. Nov 19, 2009 #3
    If you haven't already solved it, hopefully I can be of some help....!

    You would probably need to mention what the number should be if the two genes assorted independently. There would be four different combinations, each with a probability of 0.25. Of 40 children, 10 should have AbBb, 10 Aabb, etc. Then mention what the actual number of children with each are and perhaps note the ratio? For example, the AaBb should be alleles for 10 children, but it makes up 18: [tex]\frac{18}{10} = 1.8[/tex], its nearly double what it ‘should’ be.

    If you look at the two ‘under-represented’ combinations, look at how the F1 generation received the combination of alleles it has for the two genes, and look at the possible combinations for crossing over in meiosis in the F1 generation, you can deduce a possible reason why they are under-represented. If two genes are spaced far apart, there is a higher probability of crossing over occurring between them, than if they were closer together.
    I hope this makes sense….!
  5. Nov 19, 2009 #4
    You were a great help! Thank you so much! :) :) :)
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