Some members of david's family have an autosomal recessive disease. david does not have the disease; neither do his parents, nor his two brothers. his maternal grandfather has the disease, his paternal grandmother has the disease, and his sister has the disease. draw a pedigree chart to represent the geno- types of all grandparents, parents, and children. next to each person, write his or her possible genotype

A pedigree shows the genotypes of the family members 
in autosomal recessive disorders, the diseased genes are inherited from the parents. For the person to get the disease both diseased genes should be there in the genotype as its a recessive disorder.
the dominant gene - H
   recessive gene    - h
for a person to get a disease, genotype should be hh, as its autosomal recessive. If the person is normal he/ she could have the genotype HH or could be Hh and thats called a carrier.
the offspring will receive one gene from the mother and one from the father 

Twenty one miles per hour