Simple Mendelian genetics in humans

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Mendelian traits behave according to the model of monogenic or simple gene inheritance in which one gene corresponds to one trait. Discrete traits (as opposed to continuously varying traits such as height) with simple Mendelian inheritance patterns are relatively rare in nature, and many of the clearest examples in humans cause disorders. Discrete traits found in humans are common examples for teaching genetics.

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Mendelian model

According to the model of Mendelian inheritance, alleles may be dominant or recessive, one allele is inherited from each parent, and only those who inherit a recessive allele from each parent exhibit the recessive phenotype. Offspring with either one or two copies of the dominant allele will display the dominant phenotype.

Very few phenotypes are purely Mendelian traits. Common violations of the Mendelian model include incomplete dominance, codominance, genetic linkage, environmental effects, and quantitative contributions from a number of genes (see: gene interactions, polygenic inheritance, oligogenic inheritance). [1] [2]

OMIM (Online Mendelian Inheritance in Man) [3] is a comprehensive database of human genotype–phenotype links. Many visible human traits that exhibit high heritability were included in the older McKusick's Mendelian Inheritance in Man. Before the discovery of genotyping, they were used as genetic markers in medicolegal practice, including in cases of disputed paternity.

Human traits with probable or uncertain simple inheritance patterns

DominantRecessiveReferences
Low heart rate High heart rate [4]
Widow's peak Straight hair line [5] [6]
Facial dimples *No facial dimples [7] [8]
Ability to taste PTC, "Taster"Unable to taste PTC, "Nontaster" [9]
Unattached (free) earlobe Attached earlobe [7] [10] [11]
Clockwise hair direction (left to right) Counter-Clockwise hair direction (right to left) [12]
Cleft chin Smooth chin [13]
Freckles No freckles [7] [14]
Wet-type earwax Dry-type earwax [10] [15]
Roman nose No prominent bridge [16]
Marfan syndrome Average body proportions and connective tissue [17]
Huntington's disease No nerve damage [18]
Normal mucus lining Cystic fibrosis [19]
Photic sneeze reflex No light-induced sneeze reflex [20]
Forged chinReceding chin [16]
White forelock presentNo white forelock [21]
Ligamentous angustus Ligamentous Laxity [22]
Ability to eat sugar Galactosemia [23]
Total leukonychia and Bart pumphrey syndromePartial leukonychia [24]
Absence of fish-like body odour Trimethylaminuria [25]
Primary hyperhidrosis Little sweating in hands [26]
Lactase persistence Lactose intolerance [27]
Prominent chin (V-shaped)Less prominent chin (U-shaped) [28]
Acne prone Clear complexion [29]

See also

Related Research Articles

An allele, or allelomorph, is a variant of the sequence of nucleotides at a particular location, or locus, on a DNA molecule.

<span class="mw-page-title-main">Genetic disorder</span> Health problem caused by one or more abnormalities in the genome

A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders are the most common, the term is mostly used when discussing disorders with a single genetic cause, either in a gene or chromosome. The mutation responsible can occur spontaneously before embryonic development, or it can be inherited from two parents who are carriers of a faulty gene or from a parent with the disorder. When the genetic disorder is inherited from one or both parents, it is also classified as a hereditary disease. Some disorders are caused by a mutation on the X chromosome and have X-linked inheritance. Very few disorders are inherited on the Y chromosome or mitochondrial DNA.

The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a specific gene depends on the number of copies of each chromosome found in that species, also referred to as ploidy. In diploid species like humans, two full sets of chromosomes are present, meaning each individual has two alleles for any given gene. If both alleles are the same, the genotype is referred to as homozygous. If the alleles are different, the genotype is referred to as heterozygous.

<span class="mw-page-title-main">Heredity</span> Passing of traits to offspring from the species parents or ancestor

Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents. Through heredity, variations between individuals can accumulate and cause species to evolve by natural selection. The study of heredity in biology is genetics.

<span class="mw-page-title-main">Mendelian inheritance</span> Type of biological inheritance

Mendelian inheritance is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and later popularized by William Bateson. These principles were initially controversial. When Mendel's theories were integrated with the Boveri–Sutton chromosome theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics. Ronald Fisher combined these ideas with the theory of natural selection in his 1930 book The Genetical Theory of Natural Selection, putting evolution onto a mathematical footing and forming the basis for population genetics within the modern evolutionary synthesis.

<span class="mw-page-title-main">Dominance (genetics)</span> One gene variant masking the effect of another in the other copy of the gene

In genetics, dominance is defined as the interactions between alleles at the same locus on homologous chromosomes and the associated phenotype. In the case of complete dominance, one allele in a heterozygote individual completely overrides or masks the phenotypic contribution of the other allele. The overriding allele is referred to as dominant and the masked one recessive. Complete dominance, also referred to as Mendelian inheritance, follow Mendel's laws of segregation. The first law states that each allele in a pair of genes is separated at random and have an equal probability of being transferred to the next generation, while the second law states that the distribution of allele variants is done independently of each other. However, this is not always the case as not all genes segregate independently and violations of this law are often referred to as "non-Mendelian inheritance".

<span class="mw-page-title-main">Punnett square</span> Tabular summary of genetic combinations

The Punnett square is a square diagram that is used to predict the genotypes of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach in 1905. The diagram is used by biologists to determine the probability of an offspring having a particular genotype. The Punnett square is a tabular summary of possible combinations of maternal alleles with paternal alleles. These tables can be used to examine the genotypical outcome probabilities of the offspring of a single trait (allele), or when crossing multiple traits from the parents. The Punnett square is a visual representation of Mendelian inheritance. For multiple traits, using the "forked-line method" is typically much easier than the Punnett square. Phenotypes may be predicted with at least better-than-chance accuracy using a Punnett square, but the phenotype that may appear in the presence of a given genotype can in some instances be influenced by many other factors, as when polygenic inheritance and/or epigenetics are at work.

A quantitative trait locus (QTL) is a locus that correlates with variation of a quantitative trait in the phenotype of a population of organisms. QTLs are mapped by identifying which molecular markers correlate with an observed trait. This is often an early step in identifying the actual genes that cause the trait variation.

Online Mendelian Inheritance in Man (OMIM) is a continuously updated catalog of human genes and genetic disorders and traits, with a particular focus on the gene-phenotype relationship. As of 28 June 2019, approximately 9,000 of the over 25,000 entries in OMIM represented phenotypes; the rest represented genes, many of which were related to known phenotypes.

<span class="mw-page-title-main">Victor A. McKusick</span> American geneticist

Victor Almon McKusick was an American internist and medical geneticist, and Professor of Medicine at the Johns Hopkins Hospital, Baltimore. He was a proponent of the mapping of the human genome due to its use for studying congenital diseases. He is well known for his studies of the Amish. He was the original author and, until his death, remained chief editor of Mendelian Inheritance in Man (MIM) and its online counterpart Online Mendelian Inheritance in Man (OMIM). He is widely known as the "father of medical genetics".

<span class="mw-page-title-main">Equine coat color genetics</span> Genetics behind the equine coat color

Equine coat color genetics determine a horse's coat color. Many colors are possible, but all variations are produced by changes in only a few genes. Bay is the most common color of horse, followed by black and chestnut. A change at the agouti locus is capable of turning bay to black, while a mutation at the extension locus can turn bay or black to chestnut.

<span class="mw-page-title-main">Non-Mendelian inheritance</span> Type of pattern of inheritance

Non-Mendelian inheritance is any pattern in which traits do not segregate in accordance with Mendel's laws. These laws describe the inheritance of traits linked to single genes on chromosomes in the nucleus. In Mendelian inheritance, each parent contributes one of two possible alleles for a trait. If the genotypes of both parents in a genetic cross are known, Mendel's laws can be used to determine the distribution of phenotypes expected for the population of offspring. There are several situations in which the proportions of phenotypes observed in the progeny do not match the predicted values.

<span class="mw-page-title-main">Human genetics</span> Study of inheritance as it occurs in human beings

Human genetics is the study of inheritance as it occurs in human beings. Human genetics encompasses a variety of overlapping fields including: classical genetics, cytogenetics, molecular genetics, biochemical genetics, genomics, population genetics, developmental genetics, clinical genetics, and genetic counseling.

A polygene is a member of a group of non-epistatic genes that interact additively to influence a phenotypic trait, thus contributing to multiple-gene inheritance, a type of non-Mendelian inheritance, as opposed to single-gene inheritance, which is the core notion of Mendelian inheritance. The term "monozygous" is usually used to refer to a hypothetical gene as it is often difficult to distinguish the effect of an individual gene from the effects of other genes and the environment on a particular phenotype. Advances in statistical methodology and high throughput sequencing are, however, allowing researchers to locate candidate genes for the trait. In the case that such a gene is identified, it is referred to as a quantitative trait locus (QTL). These genes are generally pleiotropic as well. The genes that contribute to type 2 diabetes are thought to be mostly polygenes. In July 2016, scientists reported identifying a set of 355 genes from the last universal common ancestor (LUCA) of all organisms living on Earth.

<span class="mw-page-title-main">Test cross</span>

Under the law of dominance in genetics, an individual expressing a dominant phenotype could contain either two copies of the dominant allele or one copy of each dominant and recessive allele. By performing a test cross, one can determine whether the individual is heterozygous or homozygous dominant.

A phene is an individual genetically determined characteristic or trait which can be possessed by an organism, such as eye colour, height, behavior, tooth shape or any other observable characteristic.

<span class="mw-page-title-main">Mendelian traits in humans</span>

Mendelian traits in humans are human traits that are substantially influenced by Mendelian inheritance. Most – if not all – Mendelian traits are also influenced by other genes, the environment, immune responses, and chance. Therefore no trait is purely Mendelian, but many traits are almost entirely Mendelian, including canonical examples, such as those listed below. Purely Mendelian traits are a minority of all traits, since most phenotypic traits exhibit incomplete dominance, codominance, and contributions from many genes. If a trait is genetically influenced, but not well characterized by Mendelian inheritance, it is non-Mendelian.

Classical genetics is the branch of genetics based solely on visible results of reproductive acts. It is the oldest discipline in the field of genetics, going back to the experiments on Mendelian inheritance by Gregor Mendel who made it possible to identify the basic mechanisms of heredity. Subsequently, these mechanisms have been studied and explained at the molecular level.

Oligogenic inheritance describes a trait that is influenced by a few genes. Oligogenic inheritance represents an intermediate between monogenic inheritance in which a trait is determined by a single causative gene, and polygenic inheritance, in which a trait is influenced by many genes and often environmental factors.

<span class="mw-page-title-main">Complex traits</span>

Complex traits, also known as quantitative traits, are traits that do not behave according to simple Mendelian inheritance laws. More specifically, their inheritance cannot be explained by the genetic segregation of a single gene. Such traits show a continuous range of variation and are influenced by both environmental and genetic factors. Compared to strictly Mendelian traits, complex traits are far more common, and because they can be hugely polygenic, they are studied using statistical techniques such as quantitative genetics and quantitative trait loci (QTL) mapping rather than classical genetics methods. Examples of complex traits include height, circadian rhythms, enzyme kinetics, and many diseases including diabetes and Parkinson's disease. One major goal of genetic research today is to better understand the molecular mechanisms through which genetic variants act to influence complex traits.

References

  1. ↑ Dobzhansky T. (1970): Mankind evolving: The evolution of the human species. Bantam Books, New York, ISBN   05526-539-0X; ISBN   978-05526-5390-9.
  2. ↑ Hadžiselimović R. (2005): Bioanthropology - Biodiversity of recent man. Institute for Genetic Engineering and Biotechnology (INGEB), Sarajevo, ISBN   9958-9344-2-6. (in Bosnian).
  3. ↑ OMIM-http://www.omim.org/
  4. ↑ Benson, D. Woodrow; Wang, Dao W.; Dyment, Macaira; Knilans, Timothy K.; Fish, Frank A.; Strieper, Margaret J.; Rhodes, Thomas H.; George, Alfred L. (2003). "Congenital sick sinus syndrome caused by recessive mutations in the cardiac sodium channel gene (SCN5A)". Journal of Clinical Investigation. 112 (7): 1019–1028. doi:10.1172/JCI18062. PMC   198523 . PMID   14523039.
  5. ↑ Campbell, Neil; Reece, Jane (2005). Biology. San Francisco: Benjamin Cummings. p. 265. ISBN   0-07-366175-9.
  6. ↑ McKusick, Victor A. (10 February 2009). "Widow's Peak". Online Mendelian Inheritance in Man. Johns Hopkins University. 194000.
  7. 1 2 3 "Genetics/Reproduction". ScienceNet - Life Science. Singapore Science Centre. Archived from the original on 2003-09-25.
  8. ↑ McKusick, Victor A. (25 June 1994). "Dimples, Facial". Online Mendelian Inheritance in Man. Johns Hopkins University. 126100.
  9. ↑ Wooding, Stephen (28 June 2004). "Natural selection at work in genetic variation to taste". Medical News Today. Archived from the original on 2007-12-13.
  10. 1 2 Cruz-Gonzalez, L.; Lisker, R. (1982). "Inheritance of ear wax types, ear lobe attachment and tongue rolling ability". Acta Anthropogenet. 6 (4): 247–54. PMID   7187238.
  11. ↑ McKusick, Victor A.; Lopez, A (30 July 2010). "Earlobe Attachment, Attached vs. Unattached". Online Mendelian Inheritance in Man. Johns Hopkins University. 128900.
  12. ↑ McDonald, John H. (8 December 2011). "Hair Whorl". Myths of Human Genetics. University of Delaware.
  13. ↑ McKusick, Victor A. (23 March 2013). "Cleft Chin". Online Mendelian Inheritance in Man. Johns Hopkins University. 119000.
  14. ↑ Xue-Jun Zhang; et al. (2004). "A Gene for Freckles Maps to Chromosome 4q32–q34". Journal of Investigative Dermatology. 122 (2): 286–290. doi: 10.1046/j.0022-202x.2004.22244.x . PMID   15009706.
  15. ↑ McKusick, Victor A.; O'Neill, Marla J. F. (22 November 2010). "Apocrine Gland Secretion, Variation in". Online Mendelian Inheritance in Man. Johns Hopkins University. 117800.
  16. 1 2 "Mendelian Traits in Humans" (PDF). Human Genetics. San Diego Supercomputer Center (SDSC).
  17. ↑ Chen, Harold (2019-11-10). Buehler, Bruce (ed.). "Genetics of Marfan Syndrome". Medscape. WebMD LLC.
  18. ↑ Stafford, Kate; Mannor, Michael. "Mutations and Genetic Disease". Genetic Diseases. ThinkQuest. Archived from the original on 2007-01-03.
  19. ↑ "Autosomal Recessive: Cystic Fibrosis, Sickle Cell Anemia, Tay Sachs Disease". Medical Genetics. Children's Hospital of Pittsburgh. 3 February 2008. Archived from the original on 2009-08-24.
  20. ↑ Schrock, Karen (10 January 2008). "Looking at the Sun Can Trigger a Sneeze". Scientific American. Archived from the original on 2011-03-19.
  21. ↑ "Inherited Human Traits". EdQuest. Archived from the original on 2012-02-01.
  22. ↑ Scott, C. I. (1971). "Unusual facies, joint hypermobility, genital anomaly and short stature: A new dysmorphic syndrome". Birth Defects Original Article Series. 7 (6): 240–246. PMID   5173168.
  23. ↑ Fankhauser, D. B. (2 Feb 2006). "Human Heritable Traits". University of Cincinnati Clermont College. Archived from the original on 2012-02-23.
  24. ↑ Tüzün, Yalçın; Karaku, Özge (2009). "Leukonychia" (PDF). Journal of the Turkish Academy of Dermatology. JTAD. Archived from the original (PDF) on 2016-03-03. Retrieved 2015-02-23.
  25. ↑ "Learning About Trimethylaminuria". genome.gov. National Human Genome Research Institute.
  26. ↑ Kaufmann, Horacio; Saadia, Daniela; Polin, Charlene; et al. (10 January 2003). "Primary hyperhidrosis - Evidence for autosomal dominant inheritance" (PDF). Clinical Autonomic Research. 13 (2): 96–98. doi:10.1007/s10286-003-0082-x. PMID   12720093. S2CID   37824317.
  27. ↑ Bowen, R. (25 April 2009). "Lactose Intolerance (Lactase Non-Persistence)". Colorado State University.
  28. ↑ Jablecki, Donna Mae. "Variations on a Human Face" (PDF). Science Experiments on File. Facts on File.
  29. ↑ Strickland, Barbara. "Acne is a Four Letter Word". Sage Advice. Barbara Strickland. Archived from the original on 2006-02-07.
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