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 the same alleles, give the possible genotypes for II-2, II-3, and II-4.

Verified step by step guidance

1. Step 1: Understand the inheritance pattern. Autosomal recessive conditions require two copies of the recessive allele (aa) for the phenotype to be expressed. Individuals with one dominant and one recessive allele (Aa) are carriers but do not express the condition.
2. Step 2: Analyze the pedigree. Individual II-1 has the autosomal recessive condition, meaning their genotype must be homozygous recessive (aa). This implies that both parents (I-1 and I-2) must be carriers (Aa) since they passed on the recessive allele to II-1.
3. Step 3: Determine the possible genotypes for II-2. Since II-2 is a sibling of II-1, they could inherit either two dominant alleles (AA), one dominant and one recessive allele (Aa), or two recessive alleles (aa). However, the phenotype of II-2 (whether they express the condition or not) will help narrow down the possibilities.
4. Step 4: Determine the possible genotypes for II-3. If II-3 is unaffected, they could be either homozygous dominant (AA) or heterozygous (Aa). If II-3 is affected, their genotype must be homozygous recessive (aa).
5. Step 5: Determine the possible genotypes for II-4. Similar to II-2 and II-3, II-4's genotype depends on whether they express the condition. If unaffected, they could be AA or Aa. If affected, they must be 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, one inherited from each parent. In this case, if a child has an autosomal recessive condition, both parents must either be carriers (heterozygous) or affected (homozygous recessive). This pattern is crucial for predicting the genotypes of other family members in the pedigree.

Genotype and Phenotype

The genotype refers to the genetic makeup of an individual, specifically the alleles present at a given locus, while the phenotype is the observable expression of that genotype. In the context of the pedigree, understanding the relationship between genotype and phenotype helps in determining the possible genotypes of siblings based on the known condition of one child.

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two individuals. By inputting the possible alleles of the parents, it allows for the visualization of potential genotypes for offspring. This tool is particularly useful in determining the likelihood of each child inheriting the autosomal recessive condition or being a carrier.