Biology Pedigree Project
Optional version for adopted or special circumstance families
Here is information about a trait, your hypothetical family, and who has or does not have the trait
in this family. There are also several questions that must be answered in your evaluation.
Trait: Straight pinky finger is Dominant (F), bent pinky finger is recessive (ff), according
to our lab on Mendelian human traits. On your pedigree chart, only shade in all who
have a bent pinky.
You are the third child in a family of four children. You have a bent pinky finger. Your oldest
brother has it too. You have an older sister and a younger sister, both of whom have straight
pinkies. Both your parents have straight pinkies.
Your grandma on mom’s side is dead and no one checked before her death as to whether her
pinky was straight or not. Her husband (grandpa on mom’s side) has a bent pinky.
Your mom has an older brother (uncle 1A) with a bent pinky and an older sister (aunt 2A) with a
bent pinky. Your uncle 1A is married, his wife and both female children (your first cousins)
have bent pinkies. One of these cousins is married and has a female child with a straight pinky.
Your aunt 2A is married; her husband has a straight pinky as do their three boys.
On dad’s side, both his parents (your other grandparents) have straight pinkies. You also have a
great-grandfather (grandpa’s dad) and great-grandmother (grandpa’s mom). For some strange
reason, we know for an absolute fact that great grandma is homozygous dominant.
Your dad has three younger sisters and one younger brother (your ‘B’ aunts and uncle). Aunt 1B
is unmarried and has a bent pinky. Aunt 2B has a straight pinky, but is married to a man with a
bent pinky. They have 2 boys (first cousins), one with a bent pinky, the other doesn’t. The
cousin with the bent pinky is married and has a boy with a bent pinky.
Aunt 3B (bent pinky) was married to a man with a straight pinky and had a son with a straight
pinky. They divorced and now she is married to another man also with a straight pinky. With
this second husband, she has a daughter with a bent pinky and a son with a straight pinky.
Uncle 4B has a straight pinky and is married to a woman with a straight pinky. They have 2
daughters, one with a bent pinky, and a son with a straight pinky.
Analysis and Evaluation
1) Construct a pedigree chart illustrating every person mentioned in the paragraphs above.
Use proper pedigree charting techniques for generations, genders, and those with or
without the trait. You must label the persons using the names provided (i.e. “Aunt 3B”).
Minimum paper size is 11” x 17”.
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2) Prove to me that you understand genetics and the use of the correct terminology.
Analyze the distribution of this trait in your hypothetical family. Explain the kind of
pattern the trait follows (e.g. Mendelian, sex-linked, polygenic, incomplete dominance,
codominance, etc.) and why it follows this pattern. How did you get the trait? Are there
any apparent exceptions in this family and how might they have occurred? Predict the
possibilities for this trait in your personal family someday, that is, discuss what your
children will have based on the possibilities of your future spouse. Prove these
possibilities with Punnett Squares.
3) In addition to the above normal evaluation of the trait, you must include an answer to
these questions in your analysis. I recommend that you provide Punnett Squares to help
illustrate the answers to some of these questions.
1) What is your genotype and how did you get it?
2) What is the genotype of your mom’s mother (your grandma)? Why (or how do you know?)
3) Why does the grandchild of uncle 1A have a straight pinky?
4) What are the genotypes of dad’s parents (grandpa and grandma)? Why?
5) What is the likely genotype of your great-grandpa (dad’s side)? Is his pinky straight or bent?
Why?
6) Why does the grandson of aunt 2B have a bent pinky?
7) How is it possible for Uncle 4B to have a daughter with a bent pinky? Is this like you, why
or why not?
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