Pedigree worksheet

Name_____________________________________________________ Date __________________



Pedigrees (family trees tracing something genetic) are a bit like detective work.  I find them fun logic problems.  Good luck with these:


1. The following pedigree is tracing cystic fibrosis in a family.  Cistic fibrosis is a genetic recessive disorder caused by a defective chlorine transmembrane protein pump.  Only those who are homozygous recessive (ff) show the disease.  One normal allele with mask it.  To be homozygous recessive, an individual must recieve one affected allele from each parent (they must be at least carriers (Ff)).  With all this in mind, try to figure out the genotype of each of the people in this family:

Image result for simple pedigree worksheet

I'll give you a hint: you can deduce all of the genotypes by looking at what their parents must have given them or what they gave to their offspring.


2. Now let's try a dominant trait.  Huntington's disease is a dominant genetic disorder resulting in progressive brain damage and death later in life.  One affected allele results in the disease showing up.  Therefore, if one shows the disease, one of the parents must also have had it.  If one does not have it, they must be homozygous recessive (hh).  With all this in mind, try to write down everyone's genotype:

Image result for simple pedigree worksheet dominant

Again, you can deduce everyone's genome with some detective work.


3. Lastly, let's try a sex linked pedigree.  Hemophilia is a sex-linked recessive disorder causing excessive bleeding.  It is located on the X chromosome.  Women have two copies of the allele, but men only have one.  Therefore, men are more likely to show the disease.  Women can be carriers for it.  Men are either X'Y or XY (the ' marks the defect on the X chromosome).  Women can be XX, X'X, or X'X'.  Only the last of these would show the disease.  With all this in mind, good luck figuring out everyone's genotypes:

Image result for simple pedigree worksheet sex-linked

This one is tougher and three of the people cannot be fully determined.