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.

What are the probabilities for each of the possible genotypes for II-2, II-3, and II-4?

Verified step by step guidance

1. <span>Step 1: Understand the inheritance pattern. Since the condition is autosomal recessive, an individual must inherit two copies of the recessive allele (aa) to express the condition. Carriers have one dominant and one recessive allele (Aa), and unaffected individuals with no recessive allele have two dominant alleles (AA).</span>
2. <span>Step 2: Analyze the pedigree. Individual II-1 is affected, meaning their genotype is aa. This indicates that both parents (I-1 and I-2) must be carriers (Aa) because they have passed on the recessive allele to their child.</span>
3. <span>Step 3: Determine the possible genotypes for II-2, II-3, and II-4. Since both parents are carriers (Aa), each child has a 25% chance of being affected (aa), a 50% chance of being a carrier (Aa), and a 25% chance of being unaffected (AA).</span>
4. <span>Step 4: Calculate the probabilities for II-2. Since II-2 is not affected, they cannot be aa. Therefore, they have a 2/3 chance of being a carrier (Aa) and a 1/3 chance of being unaffected (AA).</span>
5. <span>Step 5: Apply the same logic to II-3 and II-4. Assuming they are also unaffected, each has a 2/3 chance of being a carrier (Aa) and a 1/3 chance of being unaffected (AA).</span>

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 be carriers of the recessive allele, even if they do not express the condition themselves.

Pedigree Analysis

A pedigree is a diagram that depicts the genetic relationships within a family over generations. It helps in tracking the inheritance of traits and can reveal patterns of inheritance, such as whether a condition is autosomal dominant or recessive, by analyzing the affected and unaffected individuals in the family.

Genotype Probabilities

Genotype probabilities refer to the likelihood of an individual inheriting a specific combination of alleles from their parents. In the context of the pedigree, calculating the probabilities for genotypes of II-2, II-3, and II-4 involves using the known genotypes of their parents and applying principles of Mendelian genetics to determine the chances of each possible genotype.