Biology Forum Genetics 3 point test

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    • #8601

      Hi, I have this data:
      A three point testcross was made in corn. The alleles C and c result in colored versus colorless seeds, Wx and wx in nonwaxy versus waxy seeds, and Sh and sh in plump versus shrunken seeds. When plants grown from seeds heterozygous for each of these pairs of alleles were testcrossed, the progeny were as follows.

      colorless, nonwaxy, shrunken 84
      colorless, nonwaxy, plump 974
      colorless, waxy, shrunken 20
      colorless, waxy, plump 2349
      colored, waxy, shrunken 951
      colored, waxy, plump 99
      colored, nonwaxy, shrunken 2216
      colored, nonwaxy, plump 15

      and I need to find: a) the genotype of the heterozygous parent, b) the order of the three genes, c) the genetic distance between each gene and d) calculate interference

      I have done the problem, just wondering if I am right…….
      Genotype of heterozygous parent: cwxSh /CWxsh
      Gene order: C Sh Wx
      Distance: C—–→Sh = 29cM
      Sh—→Wx = 3.2cM
      Interference: 44%

      my other question is, what is the easiest way to find the gene order in a problem like this? I have been searching tests, etc and I can’t find a good answer. They start to explain a visual method, but they just kinda stop and assume you know what they are talking about. I looked at the parental genotypes and the double recombinant genotypes and the order I came up with seems to work, but I am really not sure………thanks all!

    • #77985

      The easiest way to find the gene order is to look at the most numerous phenotypes which constitute your two parents. Now the least numerous is the double crosses(middle gene switched). So example:

      Most: AB+C / A+BC+
      Least: A+B+C / ABC+

      Gene order BAC or CAB

    • #78002

      Well, I am still confused…not sure what exactly is switching. I know my parentals and double recombinants, and that lead me to the folowing gene order:
      Parentals: cwxSh /CWxsh = Gene order: C Sh Wx
      double recombinants: CWxSh/cwxsh
      Also, when listing the gene order, do you list the dominants? Sorry, just feeling really lost and I am sure it is quite simple…..Are my answers correct?

    • #78005

      Sorry, by switches I mean double recombinants.

    • #78015

      sorry, I am still not following……..thanks for trying though! I will try to figure it out on my own

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