The accompanying pedigree shows a family in which one child (II-1) has an autosomal recessive condition. On the basis of this fact alone, provide the following information.

Using A for the dominant allele and a for the recessive allele, give the genotypes for I-1, I-2, and II-1.

Verified step by step guidance

1. Step 1: Understand the inheritance pattern. The problem states that the condition is autosomal recessive, meaning that an individual must inherit two copies of the recessive allele (a) to express the condition. Individuals with one dominant allele (A) and one recessive allele (a) are carriers but do not express the condition.
2. Step 2: Analyze the pedigree. II-1 is affected by the autosomal recessive condition, so their genotype must be homozygous recessive (aa). This is because they inherited one recessive allele from each parent.
3. Step 3: Determine the genotypes of I-1 and I-2 (the parents of II-1). Since II-1 is affected, both parents must have at least one recessive allele (a) to pass it on. Therefore, I-1 and I-2 must be carriers, meaning their genotypes are heterozygous (Aa).
4. Step 4: Confirm the reasoning. For II-1 to inherit the condition, both parents (I-1 and I-2) must contribute a recessive allele (a). This aligns with the autosomal recessive inheritance pattern.
5. Step 5: Summarize the genotypes. Based on the analysis, the genotypes are: I-1 = Aa, I-2 = Aa, and II-1 = aa.

Key Concepts

Autosomal Recessive Inheritance

Autosomal recessive inheritance occurs when a trait or condition is expressed only when an individual has two copies of the recessive allele (aa). If an individual has one dominant allele (A), they will not express the condition and are considered a carrier (Aa). This pattern of inheritance is crucial for understanding how traits are passed through generations, especially in pedigree analysis.

Genotype vs. Phenotype

The genotype refers to the genetic makeup of an individual, specifically the alleles they carry (e.g., AA, Aa, or aa), while the phenotype is the observable expression of that genotype (e.g., having a certain condition or trait). In the context of the question, determining the genotypes of the individuals in the pedigree is essential to understand the inheritance pattern of the autosomal recessive condition.

Pedigree Analysis

Pedigree analysis is a method used to trace the inheritance of traits through generations in a family. It involves constructing a diagram that represents family relationships and the presence or absence of specific traits. By analyzing the pedigree, one can infer the genotypes of individuals based on the phenotypes of affected and unaffected family members, which is critical for solving the given question.