SR.GENETICS.6D
BIOLOGY CURRICULUM 2006
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 unmbered individuals. Write individual genotypes on the lines provided.
PEDIGREE 1: Autosomal Dominant Trait: Huntington’s Disease (H, h)
Genotypes:
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BIOLOGY CURRICULUM 2006
1. ______
4. ______
2. ______
5. ______
3. ______
6. ______
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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 color-blindness 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.
Genotypes:
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1. ______
4. ______
2. ______
5. ______
3. ______
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PEDIGREE 3: Codominant Trait: Blood Type (A, B, O)
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.
ANALYSIS
Describe three ways that pedigrees and pedigree analysis are helpful or useful.
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