LMS is very rare human hereditary disorder resulting in spastic para paraplegia and mental retardation. LMS is caused by a recessive allele with Mendelian inheritance. A couple, Ross and Rachel would like to have children. However, Ross’s great-great grandfather was known to have had a daughter(from a previous marriage, not with Ross’s great-great grandma) who suffered from LMS. Rachel has a brother who has LMS. Now, Ross and Rachel are considering having a child.

a. Draw a pedigree of the above family.
b. What is the prob. that Ross and Rachel’s first child with also have LMS?