LAB: PEDIGREES
PROCEDURE
Pedigrees are one way that scientists study inheritance patterns
for various genetic traits including
diseases. Scientists first must research a family for a specific trait.
This often includes at least three
generations. This process allows them to locate marriages and births while
identifying afflicted individuals.
There is a designated set of symbols used by geneticists to indicate gender,
affliction, marriages, births,
deaths, etc. Geneticists then use the information they have gathered to
determine the genotypes of all
individuals connected in the pedigree.
In this lab you will be given 5 pedigrees.
One is labeled sample. It is suggested you start with this
pedigree because it is believed to be simpler. You will also be given
a second pedigree. For both of these
pedigrees you are to identify the symbols and connections of the individuals
and use this information to
determine the genotypes for the individuals in your pedigree.
Once you have completed the first 2 pedigrees,
you can complete the last 3 in any order. These
pedigrees consist of two family trees and one dealing with sex-linked
traits. Each of these is a little more
complex since they want names included and/or require you to deal with
the sex chromosomes also.
The following diagram includes all the
symbols necessary to understand a pedigree.
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Questions:
1. Is it possible to have two non-afflicted parents that produce an afflicted
offspring? Explain:
2. If one of the parents is afflicted does it mean that the offspring
will automatically be afflicted?
Why or why not?
3. Is there ever a situation where you would be unable to determine the
genotype of the individual?
If so, describe the situation?
4. How would genetic counselors use pedigrees?
5. Explain the difference between autosomal recessive diseases and autosomal
dominant diseases.
6. Explain the difference between sex-influenced traits and sex-linked
traits.
Pedigree Families
You are to read the following family descriptions and create a pedigree
for one of the given families. You
are to use standard pedigree symbols. Furthermore, you must label your
family members with their names.
| Family
#1 You will be tracing the presence of dimples in the Smith family. The trait is characterized using the letter (D). Having dimples is the dominant allele "D". Therefore, "d" is the recessive allele. The dimpleless people are considered the "afflicted" people. The following is a list of family members for the Smith family and their phenotypes. Grandma Smith has dimples. Grandpa Smith is dimpleless. They have three children. John Smith has dimples Susan Smith is absent of dimples Kathryn Smith has dimples Kathryn and Susan are nonidentical twins John marries Julie Johnson: Julie is absent of dimples Julie's father (Grandpa Johnson) has dimples Julie's mother (Grandma Johnson) is absent of dimples Julie's brother (Greg Johnson) has dimples John and Julie have two children Chad Smith has dimples Sarah Smith is absent of dimples Kathryn Smith marries Mike Phillips Mike is absent of dimples They have three children Jill Phillips has dimples Doug Phillips has dimples Heidi Phillips is absent of dimples Chad Smith marries Erin Kohler Erin and Chad have identical twin boys Erin Kohler has dimples Josh Smith is absent of dimples Wesley Smith is absent of dimples Josh Smith marries Abigail Mitchell They have one child Abigail has dimples Cindy Smith is absent of dimples |
Family
#2 You will be tracing the earlobe trait in the Larson family. Attached earlobes are the recessive allele (e). Free earlobes are the dominant allele (E). The people with attached earlobes are considered the "afflicted" people. The following is a list of the Larson family andtheir phenotypes. Grandma Larson has attached earlobes Grandpa Larson has free earlobes They have two children Kathy Larson has attached earlobes Christine Larson has free earlobes Christine Larson marries Joe Black They have two children Joe Black has attached earlobes Matt Black has free earlobes Mark Black has attached earlobes Mark Black marries Carol dark They have two nonidentical twins Carol dark has free earlobes Jessica Black has attached earlobes Jeremy Black has free earlobes Kathy Larson marries Richard Jones They have three children Melanie Jones has free earlobes Ken Jones has attached earlobes Hillary Jones has free earlobes Richard Jones has one sister and one pair of identical twin sisters Jamie Jones and Casey Jones are the identical twins Alison Jones (the other sister) has attached earlobes Jamie has free earlobes Casey has free earlobes Grandma Jones has free earlobes Grandpa Jones has attached earlobes Jamie Jones marries Robert White Robert White has free earlobes Richard Jones has free earlobes |