In corn, small pollen (sp) is recessive to normal pollen (sp+) and banded necrotic tissue, called zebra necrotic (zn), is recessive to normal tissue (zn+), The genes that produce these phenotypes are closely linked on chromosome 10, If no crossing over occurs between these two loci give the types of progeny expected from the following cross: a) sp + zn+/sp+zn+; sp + zn+/sp zn: sp zn/sp zn b) sp+zn/sp zn; l sp zn + / sp zn c) sp + zn/sp zn: sp zn/sp zn d) sp+zn/sp + zn; sp + zn/sp zn+; sp zn+/sp + zn; sp zn+/sp zn + e) sp + zn+/sp zn; sp + zn/sp zn

Answer: sp + zn+ / sp + zn +; sp + zn+ / sp zn; sp zn / sp zn

Explanation: f a double heterozygote is testcrossed and gametes are produced in a ratio of 1:1:1:1, this can be interpreted as unlinked genes or as genes that are 50 map units apart. Because gametes this far apart cannot be distinguished from gametes that are unlinked, it's not possible to get a ratio of gametes that indicates a distance of greater than 50 map units.

A man and a woman are trying to have children but are unsuccessful. As part of a series of tests, the man is karyotyped. His autosomes appear normal, but his sex chromosomes, shown in the following diagram, are not. The diagram also shows a normal male's sex chromosomes for reference.