Two-Point Mapping
The general strategy used to determine the genetic distance betweenlinked genes is to: 1. Make all of the genes of interestheterozygous in an individual or strain 2. Examine the gametesproduced in the heterozygous individual(s) Using our example above.You have two pure-breeding lines of plants, one with green seedsand short height (GG tt) the other with yellow seeds and tallheight (gg TT). You cross the two strains to make the genesheterozygous. What type of a cross would you perform to determinethe types of gametes being produced by the F1 heterozygousindividuals? Â Â
1. In all of the crosses below, draw two horizontal linesrepresenting the homologous chromosomes of each individual and thegenes on each chromosome. Show the P generation cross. Show thegametes produced by each parent strain (show the chromosome in thegamete)
2. Show the F1 double heterozygotes (show the chromosome lines) andthe tester stock that you would use in the testcross.
3. In your F1 double heterozygotes. a) Which gametes will be formedif crossing-over does not occur? These gametes are referred to asparental or non-recombinant gametes. Why? b) Which gametes will beformed if crossing-over does occur between the genes? These gametesare referred to as non-parental or recombinant gametes. Why?
