Pedigree Case Analysis
A verified pedigree can help in the determination of the most likely pattern of inheritance of a single-gene disorder in a family. Pedigree analysis also has relevance to the determination of approaches to testing, assessment of recurrence risks, and in some instances, prognosis (Leonard, 2007). The purpose of this paper is multi-pronged. It will analyze the pedigree of a family with the aims of identifying the pattern of inheritance of a trait, additional information required, other relatives at risk, and alternative explanations for the condition.
Additional Information Required
The pedigree illustration provided does not depict the presence of the condition in the preceding two generations on both the paternal and maternal side. Further, it does not depict the presence of carriers on either the maternal or paternal side of the family. The additional information required in this case, therefore, is a complete family history for three generations (Cummings, 2013). This information should focus on close relatives on both the paternal and maternal side. It should incorporate the medical histories of grandparents, uncles, aunts, cousins, nephews, and nieces. This history should help elicit information about the presence of the disease or condition in other family generations on each side of the family. A complete family medical history is essential in determining the pattern of inheritance of a condition (Leonard, 2007).
Pattern of Disease Inheritance
Autosomal Dominant Inheritance
Based on the limited information available, the likely modes of inheritance of the trait depicted in the pedigree are autosomal dominant or X-linked dominant (Cummings, 2013). Conditions inherited in a dominant fashion are expressed in persons with only one copy of the mutant gene. In an autosomal dominant pattern of inheritance, the mutant allele is located on one of the twenty two pairs of autosomes. Affected males and females have an equal likelyhood of passing the trait to their children due to its being dominant (Westman, 2006). Affected persons have one copy of the normal gene and one copy of the mutant gene. Therefore, every child has a 50% probability of inheriting the mutant gene. This is akin to the pedigree which shows that two of the children of these parents have inherited the condition while the other two have not.
X-linked Dominant Inheritance
In an X-linked inheritance pattern, the gene responsible for a phenotype is located on the X chromosome. Because sons do not inherit the X chromosome from their fathers, there can be no transmission from a father to a son. There can, however, be transmission from a father to a daughter. Regarding the mother, children of an affected female have a 50% probability of inheriting the X chromosome on which the mutant gene is located. Therefore, the trait depicted in the pedigree is likely to have been inherited from the mother in an X-linked dominant fashion. This is because only one daughter and one son have inherited the trait. If the defective trait was located on the father’s X-chromosome, both daughters would have inherited the trait which is not the case (Westman, 2006).
Relatives at Risk
If the condition was inherited in an autosomal dominant fashion, either parent is at risk of the condition. This is because the children must have inherited the defective gene from either parent. The siblings to the affected children are also at risk as it is possible that the condition is yet to manifest itself. If the condition was inherited in an x-linked fashion, the mother is at risk of the condition. This is because the father is unlikely to be the source of the mutant gene since only one daughter is affected.
Alternative Explanations
Alternative explanations for the above condition are the probability that the trait manifesting in the two offspring’s is controlled by more than one gene. Research has shown that the inheritance of human genetic conditions is more complex than previously thought. It involves more than the single gene patterns first described by Mendel. Other patterns of transmission of genetic disorders include mitochondrial inheritance, chromosomal inheritance, and many other atypical patterns of inheritance such as uniparental disomy, imprinting, contiguous gene disorders, and multifactorial inheritance. In addition to the many inheritance patterns, research also shows that the expression of a trait is influenced by environmental factors. Therefore, the trait in the pedigree can be explained by other patterns of inheritance as opposed to the single gene loci pattern and by environmental factors (Leonard, 2007).
Conclusion
In summary, this paper has analyzed the pedigree of a family. It has identified the additional information required in relation to the pedigree. Further, it has identified the likely pattern of inheritance of the condition. In addition, it has identified the relatives at risk of the condition. Lastly, it has described alternative explanations to the condition.
References
Cummings, M. R. (2013). Human heredity: Principles and issues. Belmont, CA: Cengage Learning.
Leonard, D. G. B. (2007). Molecular pathology in clinical practice. New York, NY: Springer Science.
Starr, C., Evers, C., & Starr, L. (2011). Biology: Concepts and applications. Belmont, CA: Cengage Learning.
Westman, J. A. (2006). Medical genetics for the modern clinician. Baltimore: Lippincott, Williams, & Wilkins.
