With news about inherited and gene-based disorders, it is useful to know basic information about genetics.
Basic Information about Genetics
Simply put, the study of heredity, genes, and genetic variation is genetics. Gregor Mendel is the “father of genetics”. This scientist from the 19th century studied “trait inheritance patterns” and how “traits were handed down from parents to offspring”. Genes are made up of DNA, which has sequences of four nucleotides called A, C, G, and T (adenine, cytosine, guanine, and thymine). These nucleotide chains are arranged in a double helix shape. A and T pair together and C and G pair together. When DNA is replicated, the strands are split and each strand becomes a template to make a new partner.1 RNA, like DNA, is a nucleic acid, but it is single-stranded. Its letters are A, C, G, and U (uracil, which pairs with adenine). RNA is found in viruses, and it is also used in protein synthesis.2 Both RNA and DNA “carry the genetic information that can be inherited form one generation to the next”.3 DNA is packed into chromosomes, which contain “tightly coiled” DNA and proteins (histones).4 Humans usually have 46 chromosome (23 pairs) in each cell. The 23rd pair differentiates between genetic males and females. Genetic females have “two copies of the X chromosome” and genetic males have “one X and one Y”.5 Genes are “the basic physical and functional unit of heredity”. Made up of DNA, they provide instructions to make proteins. According to the Human Genome Project, humans have about 25,000 genes. Every person has “two copies of each gene, one inherited from each parent”. People are unique due to alleles, which are “forms of the same gene with small differences”.6
There are several known genetic disorders. Achondroplasia, autism, breast cancer, colon cancer, Crohn’s disease, cystic fibrosis, Down syndrome, hemophilia, Huntington’s disease, osteogenesis imperfecta, ovarian cancer, Parkinson’s disease, prostate cancer, sickle cell disease, and skin cancer are some of them.7 Genetic disorders can arise in a variety of ways. With Down syndrome, patients have a partial or full extra copy of the 21st chromosome. Traits of this disorder include small stature, slant to the eyes, low muscle tone, and mental retardation. The risk of passing on this disorder increases with the age of the mother during pregnancy.8 Achondroplasia is a “short-limbed dwarfism”. Health problems associated with this include apnea, obesity, lordosis (lower back sway), bowed legs, back pain, and possibly kyphosis (“abnormal front-to-back curvature of the spine”). FGFR3 gene mutations cause achondroplasia. Both parents may even be of average size. The gene mutations can be inherited from either or both parents or arise as new mutations.9 Huntington’s disease is considered “an autosomal dominant disorder”; therefore, “only one copy of the defective gene” is needed. Every child in a family where a parent has the gene has a 50/50 chance of getting Huntington’s disease.10 Some people are predisposed to getting certain cancers due to family history and genetics.11