Question

name: ____________________________ date: ____________
pedigrees

1. what are pedigrees used for?
2. make a key for the following: unaffected female/male; carrier female/male;

affected female/male.
answer the following questions based on the pedigree below:

1. is this mostly likely a pedigree for a dominant or recessive trait?

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1. what is the relationship between i-1 and iii-3?

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1. what are the genotypes for ii-1, iii-1, and iv-1?

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1. what are the genotypes for the first generation parents (i-1 and i-2)?

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Explanation:

1. Pedigrees are standardized diagrams that track genetic traits or disorders across generations of a family, helping to identify inheritance patterns and risk of passing on traits.
2. A standard key uses consistent symbols for each category to make pedigrees interpretable.
3. Dominant traits appear in every generation, and affected parents pass the trait to offspring; here, affected individuals are present in all generations, and affected parents have affected children, which matches dominant inheritance.
4. Tracing the lineage: I-1 is the father of II-3, who is the mother of III-3, so I-1 is the grandfather of III-3.
5. For a dominant trait (let the dominant allele = $A$, recessive = $a$): unaffected individuals have two recessive alleles. II-1 is unaffected, so genotype is $aa$. III-1 is unaffected, so genotype is $aa$. IV-1 is unaffected, so genotype is $aa$.
6. The trait is dominant, and I-1 and I-2 are affected. They have an unaffected child (II-4), meaning each must carry a recessive allele to pass to the unaffected offspring, so their genotypes are $Aa$.

Answer:

1. Pedigrees are used to trace the inheritance of genetic traits or disorders through multiple generations of a family, and to determine the probability of individuals inheriting or passing on a trait.
2. Example key:

• Unaffected female: Empty circle
• Unaffected male: Empty square
• Carrier female: Half-filled circle
• Carrier male: Half-filled square
• Affected female: Fully filled circle
• Affected male: Fully filled square

1. Dominant trait
2. I-1 is the paternal grandfather of III-3 (or grandfather-granddaughter)
3. II-1: $aa$; III-1: $aa$; IV-1: $aa$
4. I-1: $Aa$; I-2: $Aa$