1. In an ab/++ cross in yeast, the following types of asci are produced:
PD ab, ab, ++, ++ 86
NPD a+, a+, +b, +b 0
T ab, a+, +b, ++ 14
What can you conclude about the chromosomal location of the a and b genes (linked or not, map distance between them if linked)? (6 pts.)
The genes are evidently linked since PD is much greater than NPD. The genes appear to be relatively closely linked. An estimate of the map distance is MD = 1/2 (%T) = 7 map units
2. What type of errors in meiosis could potentially give rise to individuals with trisomy-21? (i.e., error in which parent, at which division of meiosis). (4 pts.)
Trisomy 21 could result from errors in either parent, at either division of meiosis. (mother or father, meisosis I or II).