The Correct Answer and Explanation is:
Based on the visual evidence provided in the pedigree chart, the correct answer is that the trait is inherited in an X-linked recessive pattern.
This conclusion is drawn from a step by step analysis of the family’s genetic history. The pedigree shows an affected father, Craig, and an unaffected mother, Melanie. In X-linked recessive inheritance, the gene for the trait is located on the X chromosome. Since males have one X and one Y chromosome (XY), a single copy of the recessive allele on their X chromosome will result in them being affected. Therefore, Craig’s genotype must be XrY, where ‘r’ represents the recessive allele for the trait.
Their daughter, Jennifer, is shown as phenotypically unaffected. A daughter inherits one X chromosome from each parent. She must receive the affected Xr chromosome from her father, Craig. To be unaffected, she must have inherited a normal, dominant allele, XR, from her mother, Melanie. This makes Jennifer’s genotype XRXr. She is a carrier of the trait without expressing it herself. The specific symbol used for Jennifer, a circle with an internal pattern, is commonly used in genetics to denote a female carrier, which strongly supports this mode of inheritance.
The sons, Eric and Phil, are both unaffected. A son inherits his Y chromosome from his father and his X chromosome from his mother. For Eric and Phil to be unaffected, their genotype must be XRY. This means they both inherited the normal XR chromosome from their mother, Melanie. This information also confirms that Melanie’s genotype is XRX R. If she were a carrier (X R X r), her sons would have had a 50 percent chance of being affected. While it is possible for two sons to be unaffected by chance, the entire inheritance pattern shown fits perfectly with an X-linked recessive model where the mother is homozygous dominant.
