Notes: Tracing Traits using Pedigree Charts
Name: ______
A Pedigree chart traces the inheritance of a particular trait through several generations. It is most often used by genetic counselors to help families determine who carries a particular trait of interest.
Step 1: A genetic counselor will first gather information regarding who the family members are and how are they related. This will go back a few generations.
Step 2: The genetic counselor will then ask who in the family has the trait of interest (shows the trait).
Step 3: The genetic counselor will use this information to construct a Pedigree chart, with all the family members’ names written below each symbol.
Step 4: The genetic counselor will shade in the family members showing the trait of interest. From there, the genotypes of all individuals are determined by looking at the patterns of inheritance from generation to generation.
Pedigree Key
Squares represent males. Circlesrepresent females.
I.A horizontal line represents a marriage or mating
A vertical line extending down from the mating line represents offspring.
II.
Roman numerals to the left of the pedigree show the generations.
Birth Order: children are listed in birth order with oldest on the far left.
Identical Twins branch off of the Fraternal Twinsonly branch the same point, but are also off of the same point
connected to each other.
Shaded symbols are persons showing the trait, whether it’s dominant or recessive.
Half-shaded symbols represent persons who are carriers or heterozygous for the trait.
Circle with dot:
X-linked carrier –always female
A diagonal line through a symbol means the person is deceased.
What is a sex-linked trait?
- Genes located on the X chromosomes (some cause diseases)
- The Y is much smaller, contains few genes (Y is wimpy)
- Sex Linked Disorders
–Color Blindness (red-green)
–Hemophilia ("bleeders disease)
–Duchenne Muscular Dystrophy (weakening/loss of skeletal muscles)
- More common for males to display disorders
Punnet Square- Hemophilia example
How do you find the genotypes of the people in the chart?
- Start with a person showing the trait. Look at his/her parents.
- Decide what the parent’s genotypes would have to be to have offspring with this genotype.
- If there is not enough information to figure out a genotype, then a question mark is used to take the place of the uncertain allele.
Ex. _T?_
Example:
I.
Steve Nancy
II.
Alan
A.Is deafness a dominant or recessive trait? ______
B.To be deaf, what genotype does this son have to have?______
C.For two parents who have normal hearing to have a deaf son, they must both be carriers. What is the parents’ genotype? ______
D.Write the genotypes for the parents and son under the correct shape and half-shade any carriers.
Practice:
1. Draw a pedigree that represents Mary,who married Greg, and had2 sons and 1 daughter. Their oldest son, Josh, married April and had Ian (a boy) and Iris (a girl). Their middle child, Amy, married Scott and had identical twin boys, Brandon and Bradley. Their youngest, Zach, has not married.
Be sure to use the correct shapes (in the correct order) and connecting lines. Then label each shape with the name of the person it represents.
Answer the questions using the pedigree below.
Albinism is a genetic disorder in which a person
does not produce the brown pigment melanin.
2. Label the three generations with Roman Numerals.
3. How many albinos are there in the 3rdgeneration? ______
4. Write the genotype of each individual under their symbol.
5. What is the gender and genotype of individual D? ______
6. Half-shade those individuals that are heterozygous / carriers.
7. Is it possible for individual H to have a normal child? ______
Explain.______
8. Add the following individuals to the pedigree above:
Individual E marries a homozygous dominant individual. They have two children: a normal male and an albino female.
(Be sure to use the correct shapes and connecting lines. Then write the genotypes below each shape and shade appropriately.)
Pedigree Problems
Name: ______Period: ______Date: ______
PROBLEM # 1: The pedigree below shows the recessive trait for nearsightedness in Jane’s family. Jane, her parents, and her brother all have normal vision. Use N for the dominant allele and n for the recessive allele.
1. How many generations are represented in this pedigree? ______
2. How many children did the first couple (1 & 2) have? ______
3. How many marriages are shown on this pedigree? ______
4. What is the sex and genotype of individual # 2?______
5. What are Jane’s possible genotypes? ______
6. What is the genotype of individual 5? ______
7. What is the genotype of individual6? ______
8. What is the probability that individuals 5 & 6 will have a child that is nearsighted?______
PROBLEM # 2: Earlobes in humans are either attached (dark shapes) or detached. Answer the following questions based on the pedigree below. Use F for the dominant allele and f for the recessive allele.
9. Which trait is dominant, attached or detached earlobes? ______
10. What is the genotype of individual 1? ______
11. What is the genotype of individual 2? ______
12. What is the genotype of individual 4? ______
13. What is the genotype of individual 8? ______
14. What is the genotype of individual 9? ______
15. If individual 12 marries a heterozygous individual, what is the probability that they
will have a child with attached earlobes? ______