Multi-Factorial Inheritance

Genes are the basic hereditary units consisting of DNA sequences which code information for the synthesis of specific proteins. Phenotypic expression as well as the personality expression and behavioral patterns are also determined by these genes. Disorders caused by the abnormalities in an individual’s genome are known as genetic disorders which are either inherited or caused by mutation in the pre-existing genes (Shiel, 2010). Genetic disorders can be classified into four categories which are single-gene disorder, multi-factorial inheritance, chromosomal inheritance and mitochondrial mutations. (Refer to Figure 1, Appendix 1). Each disorder is further discussed based on their characteristics, diseases, symptoms and possible treatments.

The

Major features of this type of disorder are the occurrence of mutations in multiple genes as well as significant environmental influences may lead to this type of disorder (Shiel, 2010). The severity of the polygenic disorder is directly proportional to number of inherited deleterious genes (Kumar et al., 2005). According to Shiel (2010), breast cancer is influenced by mutation in different genes found on chromosomes 6, 11, 13, 14, 15, 17, and 22. First degree relatives of the affected individual have a risk of being affected between 2% to 7%. However, it is complicated to verify the risk of passing on this disorder as they do not have a clear-cut pattern of inheritance which eventually makes it difficult to treat multi-factorial disorders (Mehta, n.d.). According to Kumar et al. (2005), multi-factorial disorder mainly depends on family clustering factor rather than the Mendelian and chromosomal modes of

According to Campbell et al. (2008), symptoms of Down syndrome include distinctive facial appearance, short stature, heart defects, respiratory infections and mental retardation. Unlike trisomy which has an additional chromosome, monosomy lacks a chromosome, having 45, X set of chromosome complement leads to Turner’s syndrome with extent phenotypic expressions such as shorter than average, webbed neck, broad chest, swelling of hands and feet, skeletal abnormalities, and they are also infertile due to the absence of ovarian function (Shiel, 2010). Other syndrome include Klinefelter syndrome caused by 47, XXY karyotype which is commonly referred to as male hypogonadism. An extra X chromosome in their karyotype leads to phenotypic expressions like less muscular body, less facial and body hair, broader hips, larger breasts, weaker bones, and lower energy level than normal boys (Shiel, 2010). Cri du chat syndrome is an example of disorder caused by chromosomal abnormalities which is due to the alteration in chromosomal structure. It is also known as Lejeunes’s syndrome in which a part of chromosome 5 is missing, altering the morphology of that chromosome (Tyagi, Kumar1, Kumar2, Singla, & Singh, 2010). Infected individuals are mentally retarded and show unusual facial features, low birth weight and poor growth, small head, webbing of fingers or toes,