Name:______
Pedigree Studies
Background Information:
Pedigrees are not reserved for show dogs and race horses. All living things, including humans, have pedigrees. A pedigree is a diagram that shows the occurrence and appearance, or phenotype of a particular genetic trait from one generation to the next in a family. Genotypes for individuals in a pedigree usually can be determined with an understanding of inheritance and probability. In this investigation you will:
a. learn the meaning of all the symbols and lines that are used in a pedigree
b. calculate expected genotypes for all individuals shown in a pedigree.
Pre-lab Questions - (Use your notes and the Background Information above to answer the following questions):
1. What is a pedigree?
2. What can usually be determined when using a pedigree?
3. In a pedigree chart, what do the following represent:
· Roman numerals –
· Numbers –
· Squares –
· Circles –
· Horizontal lines –
· Vertical lines –
Procedure:
For all the pedigrees in this worksheet, the trait being shown is earlobe shape. Geneticists recognize two general earlobe shapes, free lobes and attached lobes (see Figure 1 below). The gene responsible for free earlobes (E) is dominant over the gene for attached earlobes (e).
Reading a Pedigree:
Use Figure 2 to answer the following questions: I
1 2
1. What is the sex of the oldest child?
2. What is the sex of the youngest child? II
1 2 3
Use Figure 3 (the same family as in Figure 2, but at a later time) to answer the following questions:
I
1 2
II
1 2 3 4
III
1
3. Which person is the son-in-law (Name him by generation # and person #)?
4. To whom is he married (Name her by generation # and person #)?
5. What sex is their child?
Determining Genotypes from a Pedigree:
To predict the genotypes for each person on a pedigree, there are two rules you must follow:
Rule 1: Assign two recessive genes to any person on a pedigree whose symbol is shaded. (These persons show the recessive trait being studied). Two small letters (in this case – ee) are written below that person’s symbol.
Rule 2: Assign one dominant gene to any person on a pedigree whose symbol is unshaded. (These persons show the dominant trait being studied). A capital letter (in this case – E_) is written below that person’s symbol.
Using these 2 rules, you can then try to predict every person’s genotype in a pedigree. There will be some people in a pedigree that you cannot predict, for those people you will write EE or Ee, as their exact genotype cannot be predicted for sure.
Use these rules to predict the genotypes for the individuals in Figure 4 below.
I
1 ___ 2 _____
II
1 2 3 4
______
III
1 ______
6. What is the genotype of I-1?
7. What is the genotype of II-3?
8. What is the genotype of II-4?
9. Could child II-3 or II-4 be EE – yes/no?
Explain.
To predict the genotype for person II-1, a different method must be used.
10. Can an EE person married to an ee person (II-2), have children with free
lobes (EE or Ee) – yes/no?
Do the Punnett square to prove your answer.
11. Can an Ee person married to an ee person (II-2), have children with free
lobes (EE or Ee) – yes/no?
Do the Punnett square to prove your answer.
In this case, the genotype for person II-1 would be ee. At some time in the future, you might be able to predict the father’s genotype. For example, if they have some children with attached earlobes (ee), then he must be Ee.
Examine this pedigree:
12. Which Punnett Square, A, B, or C, would best fit this family – circle one?
E e E e E E
E E E
E e E
A B C
13. Explain your choice.
Analysis and Conclusion Questions:
1. Draw a pedigree for a family showing 2 parents and 4 children.
· Make the 2 oldest children boys and the youngest 2 girls.
· Label the marriage line.
· Label the children’s line.
· Number the generations and each of the people.
2. On the pedigree you drew above, show that person II-3 has attached
earlobes (ee).
3. Using the pedigrees below, predict the genotypes for these families.
Write the letters on the lines provided – remember the 2 rules!
4. Examine the pedigree below – predict the genotypes for each person.
Write the letters on the lines provided – remember the 2 rules!
Answer the following questions about the pedigree in Question #4.
a. How many generations are shown?
b. How many persons have free earlobes – just write a number?
c. How many persons have attached earlobes – just write a number?
d. Identify by generation and person number, those people with attached
earlobes.
Critical Thinking Questions:
1. Can the actual genotypes of an offspring be determined by knowing the traits
of the parents – yes/no? Explain your answer.
2. What type of symbol (shaded or unshaded) on a pedigree helps you most in
determining the genotypes of all the individuals in a pedigree? Explain your
answer.