I have an issue understanding maternally and paternallyimprinted gene questions.

Here are some examples:

1. A phenotypically normal man named John is heterozygous for adeletion on chromosome 15 that contains the maternally imprintedgene SNPRN gene. Absence of SNPRN gene function results inPrader-Willi syndrome. The man marries a normal woman named Janewho does not carry the deletion. They have 2 children. Which of thefollowing statements is FALSE?

A. John inherited the chromosome with the deletion from hismother

B. There is a 25% chance that both children will havePrader-Willi syndrome

C. Half of John's sperm contain a version of the SNPRN gene thatwould be expressed in his children

D. All of Jane's eggs contain a version of the SNRPN gene thatwould be expressed in her children

E. in Jane's somatic cells, there is one active copy of theSNRPN gene.

The answer is D, but how are choices B and Etrue? I'm in a genetics course at a university so beingdetailed would be helpful please.

2. The Igf2 gene in mice encodes a growth factor gene whoseexpression is necessary for normal size. The absence of the Igf2gene products results in small mice. The Igf2 gene is a maternallyimprinted gene, meaning it gets inactivated during oogenesis infemales. A normal-sized female mouse heterozygous for a deletion ofthe Igf2 gene gives birth to a normal-sized male. This male is thencrossed to a normal female (no deletion). Assuming that this maleinherits the Igf2 deletion from his mother, what fraction of theprogeny from this male will be small?

A. 1/4 B.0 C.1/2 D.1/3 E.1

The answer is C, but again I don't understand why.