You may have heard of sex-linked diseases, like Duchenne muscular dystrophy. These display a different inheritance pattern than standard recessive or dominant diseases inherited through the other chromosomes called autosomes. For some disease genes, it is possible that being a heterozygote gives a person certain advantages. When two people have a child, there are several possibilities:. The study of genetics is complex. Alleles are different forms or variations of a gene.
They help determine the traits that are inherited from our parents, such as eye color, skin pigmentation, blood type, height, and more. Heterozygous is when different forms of a specific gene are inherited from each parent. Homozygous is when a gene inherited from each parent is identical. Basically, heterozygous means different while homozygous means the same. Genotype is a term used to define an individual's entire collection of genes. Humans share mostly similar DNA, but there are variations in certain sequences.
These varieties are what separate us from one another. Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life.
Beyond the definitions of the phenotypic complications of sickle cell disease: an update on management. Scientific World Journal. Mahalingam S, Levy LM.
Genetics of Huntington disease. American Journal of Neuroradiology. The importance of genetic diagnosis for Duchenne muscular dystrophy. J Med Genet. National Human Genome Research Institute. Genetics in Medicine 7th ed. Philadelphia, PA: Sauders Elsevier; Your Privacy Rights.
To change or withdraw your consent choices for VerywellHealth. At any time, you can update your settings through the "EU Privacy" link at the bottom of any page. These choices will be signaled globally to our partners and will not affect browsing data. We and our partners process data to: Actively scan device characteristics for identification. For example, the allele for blue eyes is recessive, therefore to have blue eyes you need to have two copies of the 'blue eye' allele.
Related Content:. What is a gene? What is inheritance? What is genetic variation? What are single gene disorders? What is a genetic disorder?
How helpful was this page? What's the main reason for your rating? Which of these best describes your occupation? Jackson RS, et al. Obesity and impaired prohormone processing associated with mutations in the human prohormone convertase 1 gene.
Nat Genet. Yeo GSH, et al. A frameshift mutation in MC4R associated with dominantly inherited human obesity. A frameshift mutation in human MC4R is associated with a dominant form of obesity. Gu W, et al. Identification and functional analysis of novel human melanocortin-4 receptor variants. Hinney A, et al. Several mutations in the melanocortin-4 receptor gene including a nonsense and a frameshift mutation associated with dominantly inherited obesity in humans.
J Clin Endocrinol Metab. Sina M, et al. Phenotypes in three pedigrees with autosomal dominant obesity caused by haploinsufficiency mutations in the melanocortin-4 receptor gene. Am J Hum Genet. Vaisse C, et al.
Melanocortin-4 receptor mutations are a frequent and heterogeneous cause of morbid obesity. J Clin Invest. Farooqi IS, et al. Dominant and recessive inheritance of morbid obesity associated with melanocortin 4 receptor deficiency. Clinical spectrum of obesity and mutations in the melanocortin 4 receptor gene.
N Engl J Med. Melanocortin-4 receptor gene: case-control study and transmission disequilibrium test confirm that functionally relevant mutations are compatible with a major gene effect for extreme obesity. Valli-Jaakola K, et al. Identification and characterization of melanocortin-4 receptor gene mutations in morbidly obese finnish children and adults.
Stutzmann F, et al. Prevalence of melanocortin-4 receptor deficiency in europeans and their age-dependent penetrance in multigenerational pedigrees. Roth CL, et al. A novel melanocortin-4 receptor gene mutation in a female patient with severe childhood obesity.
Calton MA, et al. Association of functionally significant Melanocortin-4 but not Melanocortin-3 receptor mutations with severe adult obesity in a large north American case-control study. Hum Mol Genet. A homozygous null mutation delineates the role of the Melanocortin-4 receptor in humans. Dubern B, et al. Homozygous null mutation of the Melanocortin-4 receptor and severe early-onset obesity.
J Pediatr. Perez Y, et al. UNC80 mutation causes a syndrome of hypotonia, severe intellectual disability, dyskinesia and dysmorphism, similar to that caused by mutations in its interacting cation channel NALCN. Rettenbacher E, et al. A novel non-synonymous mutation in the melanocortin-4 receptor gene MC4R in a 2-year-old Austrian girl with extreme obesity. Exp Clin Endocrinol Diabetes. Logan M, et al. Mol Genet Genomic Med. Melanocortin-4 receptor gene mutations in a Dutch cohort of obese children.
Young EH, et al. The VI polymorphism of the MC4R gene and obesity: population based studies and meta-analysis of 29 individuals. Int J Obes Lond. MacKenzie RG. Obesity-associated mutations in the human melanocortin-4 receptor gene. Red hair is a recessive trait. A person who is heterozygous for red hair has one allele for a dominant trait, like brown hair, and one allele for red hair. They can pass the red hair allele to their future children.
Some diseases are caused by mutated alleles. This risk is related to the way dominant and recessive alleles interact. If you were heterozygous for that mutated recessive allele, the normal dominant allele would take over. The disease may be expressed mildly or not at all. The cystic fibrosis transmembrane conductance regulator CFTR gene makes a protein that controls fluid movement in and out of cells.
If you inherit two mutated copies of this gene, you have cystic fibrosis CF. Every person with CF is homozygous for this mutation. The hemoglobin subunit beta HBB gene helps produce beta-globin, which is part of hemoglobin in red blood cells. Hemoglobin makes it possible for red blood cells to deliver oxygen throughout the body. In sickle cell anemia , there are two copies of an HBB gene mutation.
The mutated alleles make abnormal beta-globin, which leads to low red blood cells and poor blood supply. Normally, the PAH gene instructs cells to produce an enzyme that breaks down an amino acid called phenylalanine. This causes phenylalanine to accumulate in the tissues and blood.
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