Download Red-Green Color Blindness

Student ____________________________ Period ______ Date ________
PEDIGREE PROBLEMS
Observing the pattern of affected individuals in a pedigree can tell you
how a particular trait is inherited. You have already analyzed a
pedigree for cystic fibrosis, an autosomal recessive disease.
Autosomal recessive traits have a distinct inheritance pattern visible
in a pedigree by this formation of symbols:
Why? The only way two unaffected parents can have affected offspring is if they both
carry the recessive allele and pass it on.
How are pedigrees for cystic fibrosis and other traits the same or
different? An autosomal dominant trait has a pedigree pattern like
this:
Can you explain why? __________________________________________________
_____________________________________________________________________
PART I: IDENTIFYING GENOTPYES
This activity will help you analyze pedigrees of traits that are NOT inherited by
autosomal recessive genes.
DIRECTIONS: For each pedigree, use the key and alleles to determine the genotypes of
the unnumbered individuals. Write individual genotypes on the lines provided.
PEDIGREE 1: Autosomal Dominant Trait: Huntington’s Disease (H, h)
KEY
2
1
normal female
affected female
3
4
5
normal male
affected male
6
Genotypes:
1. ________
2. ________
3. ________
4. ________
5. ________
6. ________
Student ____________________________ Period ______ Date ________
PEDIGREE 2: Sex-Linked Recessive Trait, Colorblindness (XC , Xc , Y)
Not being able to distinguish the color red from the color green is a sex-linked trait. The
normal dominant gene is C and the defective recessive gene is symbolized c (the lower
case “c” is underlined here to distinguish it from upper case). Like hemophilia, the colorblindness gene is recessive and located on the X chromosome. Recall that heterozygous
females carry one defective copy of the gene. Sometimes, thought not always, carriers are
represented by a half-filled circle in a pedigree.
KEY
1
normal female
2
affected female
3
carrier
4
normal male
affected male
5
Genotypes:
1. ________
2. ________
4. ________
5. ________
3. ________
PEDIGREE 3: Codominant Trait: Blood Type (A, B, O)
AB
Genotypes:
A
1
B
A
B
2
3
B
4
O
A
9
B
O
5
6
A
B
A
7
8
AB
O
O
1. ________
7. ________
2. ________
8. ________
3. ________
9. ________
4. ________
10. ________
5. ________
11. ________
6. ________
12. ________
AB
A
B
10
11
O
B
12
Student ____________________________ Period ______ Date ________
PART II: PEDIGREE PATTERN IDENTIFICATION
DIRECTIONS:
1. For each pedigree, choose the form of inheritance that best explains how the trait
is passed on. Your options include autosomal recessive, autosomal dominant,
and sex-linked recessive.
2. Circle the individual or individuals that helped you identify the trait.
3. Finally, in two or three sentences, defend your choice.
Student ____________________________ Period ______ Date ________
ANALYSIS
Describe three ways that pedigrees and pedigree analysis are helpful or useful.