The gene controlling the Xg blood group alleles (Xg⁺ and Xg⁻) and the gene controlling a newly described form of inherited recessive muscle weakness called episodic muscle weakness (EMWX) (Ryan et al., 1999) are closely linked on the X chromosome in humans at position Xp22.3 (the tip of the short arm). A male with EMWX who is Xg⁻ marries a woman who is Xg⁺ and they have eight daughters and one son, all of whom are normal for muscle function, the male being Xg⁺ and all the daughters being heterozygous at both the EMWX and Xg loci. Following is a table that lists three of the daughters with the phenotypes of their husbands and children. Create a pedigree that represents all data stated above and in the following table.

Key Concepts

X-linked Inheritance

X-linked inheritance refers to the pattern of inheritance for genes located on the X chromosome. In humans, males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). This means that X-linked traits are often expressed differently in males and females, with males being more likely to express recessive traits due to having only one X chromosome.

Alleles and Genotypes

Alleles are different versions of a gene that can exist at a specific locus on a chromosome. In the context of the Xg blood group, the alleles are Xg⁺ (dominant) and Xg⁻ (recessive). The genotype refers to the specific combination of alleles an individual possesses, which can influence their phenotype, or observable traits, such as blood group and susceptibility to conditions like episodic muscle weakness.

Pedigree Analysis

Pedigree analysis is a method used to trace the inheritance of traits through generations in a family. It visually represents relationships and genetic traits among family members, allowing for the identification of patterns of inheritance, such as dominant or recessive traits. In this case, constructing a pedigree helps illustrate how the Xg blood group and EMWX are inherited among the offspring of the couple described.