Mendel Law of Inheritance Human Disorders Single Gene Diseases Paper


Mendel did most of his work using pea plants and was studding seven different characteristics, each with two contrasting traits [1]. Morgan rediscovered his laws of inheritance and further the knowledge using Drosophila as a model organism. Later discoveries confirmed that human heredity is regulated by the same laws of inheritance. Many of our characteristics are polygenic, however a number of them are controlled by a single gene, and Mendel’s work is a “solid foundation for our current understanding of single gene diseases in humans” [2]. 

Please search in the literature and present human disorder(s) that are following Mendelian type of inheritance.


2. Chial, H. (2008) Mendelian genetics: Patterns of inheritance and single-gene disorders. Nature Education 1(1):63.

Here’s 1 Nerogica Nimalan

RE: Mendel and Human Genetics


The understanding of single-gene diseases humans helps to expand our knowledge on disorders that affect humans. Monogenic disorders are diseases that are caused by a variation in one single gene. An example of a single-gene disease is phenylketonuria. This disease is autosomal recessive and caused by an inborn error of metabolism. This means that there is a deficiency of phenylalanine hydroxylase which is an enzyme that causes the catalyzation of hydroxylation of phenylalanine to tyrosine. This disorder causes mental retardation. Another single-gene disorder is Huntington’s disease. This disease is an autosomal dominant disorder. This disorder is caused by a trinucleotide CAG repeat expansion in the specific huntingtin gene.


Myers RH. Huntington’s disease genetics. NeuroRx. 2004;1(2):255-262. doi:10.1602/neurorx.1.2.255

Merritt AD, Conneally PM, Rahman NF, Drew AL. Juvenile Huntington’s chorea. In: Progress in neurogenetics. (Barbeau A, Brunette TR, eds), pp 645–650. Amsterdam: Excerpta Medica Foundation, 1969. 

Here’s 2. Ashley Lavdas

RE: Mendel and Human Genetics



There are many diseases or syndromes that are caused by multiple genes influencing a trait, making it polygenic. However, there are a handful caused by only a single gene making it a monogenic inheritance pattern.

Fragile X syndrome is an X-linked dominant disorder that occurs by transcriptional silencing of the FMR1 gene (Garber et al., 2008). The FMR-1 gene has a repeating region of CGG in the 5’ untranslated region. Individuals with Fragile X syndrome have an expanded amount of repeats in this region that prevents synthesis of the gene’s protein product. The normal amount of CGG repeats on the FMR1 gene is between 6-55. “Pre-mutation” alleles have a higher number of repeats: 56-200. These pre-mutation alleles still provide a normal gene function, but they are unstable. During DNA replication in female germ-line cells, there is a high probability of CGG repeat expansion, thus pre-mutation alleles are unstable. Phenotypically normal females that are heterozygous for pre-mutation allele are likely to have gametes with a higher number of triplet repeats. When the CGG repeat is between 200-4000, it is considered mutant. When the FMR1 gene is mutated, the FMR1 protein can’t properly form synapses (Hartwell, 2018). FMRP, the gene product of FMR1, is a protein that negatively regulates the protein synthesis of neuronal dendrites. With a mutated gene, the transcripts that are normally regulated by FMRP are overtranslated and lead to an abundance of proteins that reduces synaptic strength (Garber et al., 2008).

Fragile X syndrome may not present phenotypically or only have subtle indications. However, it is associated with a wide range of intellectual and emotional disabilities, including autism (Garber et al., 2008).


Garber, K. B., Visootsak, J., & Warren, S. T. (2008). Fragile X syndrome. European Journal of Human Genetics, 16(6), 666–672. doi:10.1038/ejhg.2008.61

Hartwell, L. (2018). Genetics: From genes to genomes (Sixth edition). McGraw-Hill Education.