5. Two different copies of chromosome 2 in corn were found to differ in their gene order.
The first chromosome had the order A B C D E • F G H I J. Each pair of adjacent letters
in the first chromosome is separated by approximately 10 cM. For example, the A to B
distance is 10 cM, as is the B-C distance, etc.. The second copy of this chromosome
has the order a b f • e d c g h i j, where the dot indicates the position of the centromere.
A. If a plant that is heterozygous for these two chromosomes were testcrossed, and the
progeny examined, approximately what frequency of recombination would you expect to
measure between H and J?
B. In that same testcross, approximately what frequency of recombination would you
expect to measure between D and E?
C. In that same testcross, approximately what frequency of recombination would you
expect between C and G?
D. A chromosome that had crossing over between C and E was recovered – how did it
arise and what genotype do you expect the chromosome to have?
E. A plant is produced in which both copies of chromosome 2 have the gene order
indicated for the second chromosome. Assuming that the chromosomes are suitably
marked (i.e. A/a, B/b etc.), approximately what frequency of recombination would you
expect to measure
- between A and B?
- between B and C?
- between C and D