Pedigree Worksheet
A. Interpreting a human Pedigree (use figure A to answer the following questions)
1. Number all individuals on the pedigree at the top of each shape (the first 3 have been numbered for you
2. In a pedigree, a square represents a male. If it is darkened he has hemophilia; if it is clear, he has normal blood
clotting.
a. How many males are there?
b. How many males have hemophilia?
3. A circle represents a female. If it is darkened, she has hemophilia; if it is clear she has normal blood clotting.
a. How many females are there?
b. How many females have hemophilia?
4. A marriage is indicated by a horizontal line connecting a circle to a square.
a. How many marriages are there?
5. A line perpendicular to a marriage line indicates the offspring. If the line ends with either a circle or a square, the
couple had only one child. However, if the line is connected to another horizontal line, then several children were
produced, each indicated by a short vertical line connected to another horizontal line. The first child born appears to
the left and the last born to the right.
a. How many children did the first couple (couple in row I) have?
b. How many children did the third couple (couple in row III) have?
6. Level I represents the first generation, level II represents the second generation
a. How many generations are there?
b. How many members are there in the fourth generation?
7. The genotype of an individual with hemophilia is easy to identify normal blood clotting is dominant (N) and
hemophilia is recessive (n). Label each of the darkened shapes with the hemophilia genotype.
8. An individual with normal blood clotting can either be homozygous dominant or heterozygous. Using the pedigree
label each of the clear circles as either “NN” or “Nn”. To know the correct genotype look at the generation before
and the generation after. If one parent has hemophilia the individual must be heterozygous. If any offspring has
hemophilia the individual must be heterozygous. If you still are not sure if the individual is homozygous dominant or
heterozygous label the genotype as “N?”
B. Determining the pattern of inheritance and assessing genotypes. (use figure B to answer the following questions)
1. Determine which characteristic is dominant- the shaded one or the clear one. Record this next to the key
2. Choose a letter and begin assigning genotypes. Write the genotypes under each symbol. Remember that
recessive individuals are always homozygous, so assign their genotypes first.
3. For some individuals with the dominant trait you will only be able to determine one allele of the genotype. For
these just write the one capital allele followed by a dash (A-).
C. Create your own pedigree
In your notebook, create a pedigree with the following information. Follow the guidelines for a pedigree that
you have learned from parts A and B when creating it.
Colorblindness is a sex-linked recessive trait. Ray and Elaine were married in 1970. They both had
normal vision. They had 2 daughters and then a son. Both daughters, Alicia and Candace, had normal vision and
never had any children of their own. The son, Mike, was colorblind. The son married Beth who had normal vision
and they had 2 children of their own, first Greg then Victoria. Victoria was colorblind, but Greg was not.
After drawing your Pedigree, shade in the individuals that are colorblind. Also under each individual (shape) write the
person’s name and their genotype.
Staple the paper with figures A and B into your notebook
Next to the page with the answers from parts A and C