Question

2. You carry out a dihybrid cross in sweet peas where you examine the flower color locus (use symbols based on "P" for this gene) and blooming time locus (use symbols based on "L" for this gene). You cross a true breeding purple- flowering, early blooming plant to a true breeding red-flowering, late blooming plant. The F1 plants are all purple- flowering and late blooming. The F1 plants were subsequently used in a testcross. The flower color locus and the blooming time locus are known to assort independently. a) Write the genotypes, using the correct notation, of the two parental plants. (2 marks) b) Write the genotype(s) of the F1 plants. (1 mark) c) Complete the table below to indicate: the genotype of gametes made by the F1, the relative proportion each of the gamete(s) is made in, and whether the gamete is PARENTAL or RECOMBINANT. (12 marks) GENOTYPE OF F1 GAMETE PROPORTION PARENTAL (P) OR RECOMBINANT (R) d) Write the genotype and indicate the phenotype of the tester plant used in the testcross. (2 marks) e) Suppose the testcross generated 840 progeny, how many would be purple-flowering, early blooming? (1 mark)

Answer 1

c) a) Purple = = P Genotype of F1 gamete Proportion Parental (P) or recombinant Red = p PL Recombinant PI Late blooming = L Early blooming = 1 Parental genotypes: PPll x ppLL b) Genotype of F1: PpLI 1/4 1/4 1/4 Parental PL Parental pl 1/4 recombinant d) In a testcross, the tester plant is always homozygous recessive for both genes Genotype: ppli Phenotype: Red, early blooming e) First, you should make the Punnett Square PpLI x poll PL PI pL ppLI PpLI PpLI PpLI PpLI pl pl Poll Poll Poll There are 4/16 purple, early blooming (Ppll). To determinate the number out of 840 progeny, multiply the fraction by the total number of progeny 840 x 4/16 = 210. 210 individuals out of 840 progeny will be purple, early blooming pl ppll poll poll poll ppLI ppli ppli pl Poll