Practice trihybrid crosses

Trihybrid examples

A) The four sets of data above form a continuous map over six loci.
    1) Determine the locus order and distances among loci for each set of data.
    2) Determine the gene order and the distances between all six loci.


In each case, a triple dominant homozygote
parent (ABD // ABD) has been crossed with a triple recessive homozygote tester (abd // abd) to produce an F1 triple heterozygote (AaBbDd). The heterozygote was then back-crossed to the tester strain (abd // abd), and the numbers of resultant progeny counted. A '+' symbol indicates the  phenotype corresponding to the dominant allele at each locus. So, each parental cross can also be written in the form   a+b+d+ // a+b+d+ X abd // abd , or in short-hand form +++ // +++ X abd // abd .



Practice trihybrid crosses 2

B)
The four sets of data above form a continuous map over six loci.
    1) Determine the locus order and distances among loci for each set of data.
    2) Determine the gene order and the distances between all six loci.

Each of the P parents is a triple homozygote as above, however the cis / trans phase relationships among the three loci in the various crosses are not as simple as in the first set of examples. The F1 offspring were crossed with a triple recessive homozygote, as above.


Hints: First determine the Parental and Double Recombinant phenotypes. All distances in both maps should work out to round numbers. The correct gene order should spell a word.


All text material ©2012 by Steven M. Carr