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Human genetics

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.

Genes are the common factor of the qualities of most human-inherited traits. Study of human genetics can answer questions about human nature, can help understand diseases and the development of effective treatment and help us to understand the genetics of human life. This article describes only basic features of human genetics; for the genetics of disorders please see: medical genetics.

Representation of the double helix structure of human DNA

Genetic differences and inheritance patterns

 
Autosomal dominant pattern, a 50/50 chance

Inheritance of traits for humans are based upon Gregor Mendel's model of inheritance. Mendel deduced that inheritance depends upon discrete units of inheritance, called factors or genes.[1]

Autosomal dominant inheritance

Autosomal traits are associated with a single gene on an autosome (non-sex chromosome)—they are called "dominant" because a single copy—inherited from either parent—is enough to cause this trait to appear. This often means that one of the parents must also have the same trait, unless it has arisen due to an unlikely new mutation. Examples of autosomal dominant traits and disorders are Huntington's disease and achondroplasia.

Autosomal recessive inheritance

 
Autosomal recessive inheritance, a 25% chance

Autosomal recessive traits is one pattern of inheritance for a trait, disease, or disorder to be passed on through families. For a recessive trait or disease to be displayed two copies of the trait or disorder needs to be presented. The trait or gene will be located on a non-sex chromosome. Because it takes two copies of a trait to display a trait, many people can unknowingly be carriers of a disease. From an evolutionary perspective, a recessive disease or trait can remain hidden for several generations before displaying the phenotype. Examples of autosomal recessive disorders are albinism, cystic fibrosis.

X-linked and Y-linked inheritance

X-linked genes are found on the sex X chromosome. X-linked genes just like autosomal genes have both dominant and recessive types. Recessive X-linked disorders are rarely seen in females and usually only affect males. This is because males inherit their X chromosome and all X-linked genes will be inherited from the maternal side. Fathers only pass on their Y chromosome to their sons, so no X-linked traits will be inherited from father to son. Men cannot be carriers for recessive X linked traits, as they only have one X chromosome, so any X linked trait inherited from the mother will show up.

Females express X-linked disorders when they are homozygous for the disorder and become carriers when they are heterozygous. X-linked dominant inheritance will show the same phenotype as a heterozygote and homozygote. Just like X-linked inheritance, there will be a lack of male-to-male inheritance, which makes it distinguishable from autosomal traits. One example of an X-linked trait is Coffin–Lowry syndrome, which is caused by a mutation in ribosomal protein gene. This mutation results in skeletal, craniofacial abnormalities, mental retardation, and short stature.

X chromosomes in females undergo a process known as X inactivation. X inactivation is when one of the two X chromosomes in females is almost completely inactivated. It is important that this process occurs otherwise a woman would produce twice the amount of normal X chromosome proteins. The mechanism for X inactivation will occur during the embryonic stage. For people with disorders like trisomy X, where the genotype has three X chromosomes, X-inactivation will inactivate all X chromosomes until there is only one X chromosome active. Males with Klinefelter syndrome, who have an extra X chromosome, will also undergo X inactivation to have only one completely active X chromosome.

Y-linked inheritance occurs when a gene, trait, or disorder is transferred through the Y chromosome. Since Y chromosomes can only be found in males, Y linked traits are only passed on from father to son. The testis determining factor, which is located on the Y chromosome, determines the maleness of individuals. Besides the maleness inherited in the Y-chromosome there are no other found Y-linked characteristics.

Pedigrees analysis

 
An example of a family pedigree displaying an autosomal recessive trait

A pedigree is a diagram showing the ancestral relationships and transmission of genetic traits over several generations in a family. Square symbols are almost always used to represent males, whilst circles are used for females. Pedigrees are used to help detect many different genetic diseases. A pedigree can also be used to help determine the chances for a parent to produce an offspring with a specific trait.

Four different traits can be identified by pedigree chart analysis: autosomal dominant, autosomal recessive, x-linked, or y-linked. Partial penetrance can be shown and calculated from pedigrees. Penetrance is the percentage expressed frequency with which individuals of a given genotype manifest at least some degree of a specific mutant phenotype associated with a trait.

Inbreeding, or mating between closely related organisms, can clearly be seen on pedigree charts. Pedigree charts of royal families often have a high degree of inbreeding, because it was customary and preferable for royalty to marry another member of royalty. Genetic counselors commonly use pedigrees to help couples determine if the parents will be able to produce healthy children.

Karyotype

 
Micrographic karyogram of a human male, showing 46 chromosomes including XY sex chromosomes
 
Schematic karyogram of a human, with annotated bands and sub-bands. It shows dark and white regions on G banding. It shows 22 homologous chromosomes, both the male (XY) and female (XX) versions of the sex chromosome (bottom right), as well as the mitochondrial genome (at bottom left).

A karyotype is a very useful tool in cytogenetics. A karyotype is picture of all the chromosomes in the metaphase stage arranged according to length and centromere position. A karyotype can also be useful in clinical genetics, due to its ability to diagnose genetic disorders. On a normal karyotype, aneuploidy can be detected by clearly being able to observe any missing or extra chromosomes.[1]

Giemsa banding, g-banding, of the karyotype can be used to detect deletions, insertions, duplications, inversions, and translocations. G-banding will stain the chromosomes with light and dark bands unique to each chromosome. A FISH, fluorescent in situ hybridization, can be used to observe deletions, insertions, and translocations. FISH uses fluorescent probes to bind to specific sequences of the chromosomes that will cause the chromosomes to fluoresce a unique color.[1]

Genomics

Genomics is the field of genetics concerned with structural and functional studies of the genome.[1] A genome is all the DNA contained within an organism or a cell including nuclear and mitochondrial DNA. The human genome is the total collection of genes in a human being contained in the human chromosome, composed of over three billion nucleotides.[2] In April 2003, the Human Genome Project was able to sequence all the DNA in the human genome, and to discover that the human genome was composed of around 20,000 protein coding genes.

Medical genetics

Medical genetics is the branch of medicine that involves the diagnosis and management of hereditary disorders. Medical genetics is the application of genetics to medical care. It overlaps human genetics, for example, research on the causes and inheritance of genetic disorders would be considered within both human genetics and medical genetics, while the diagnosis, management, and counseling of individuals with genetic disorders would be considered part of medical genetics.

Population genetics

Population genetics is the branch of evolutionary biology responsible for investigating processes that cause changes in allele and genotype frequencies in populations based upon Mendelian inheritance.[3] Four different forces can influence the frequencies: natural selection, mutation, gene flow (migration), and genetic drift. A population can be defined as a group of interbreeding individuals and their offspring. For human genetics the populations will consist only of the human species. The Hardy–Weinberg principle is a widely used principle to determine allelic and genotype frequencies.

Mitochondrial DNA

In addition to nuclear DNA, humans (like almost all eukaryotes) have mitochondrial DNA. Mitochondria, the "power houses" of a cell, have their own DNA. Mitochondria are inherited from one's mother, and their DNA is frequently used to trace maternal lines of descent (see mitochondrial Eve). Mitochondrial DNA is only 16kb in length and encodes for 62 genes.

 
XY Chromosomes

Genes and sex

The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects (Drosophila), and some plants (Ginkgo). In this system, the sex of an individual is determined by a pair of sex chromosomes (gonosomes). Females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males have two distinct sex chromosomes (XY), and are called the heterogametic sex.

X-linked traits

Sex linkage is the phenotypic expression of an allele related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of inheritance. Since humans have many more genes on the X than the Y, there are many more X-linked traits than Y-linked traits. However, females carry two or more copies of the X chromosome, resulting in a potentially toxic dose of X-linked genes.[4]

To correct this imbalance, mammalian females have evolved a unique mechanism of dosage compensation. In particular, by way of the process called X-chromosome inactivation (XCI), female mammals transcriptionally silence one of their two Xs in a complex and highly coordinated manner.[4]

X-link dominant X-link recessive References
Alport syndrome Absence of blood in urine
Coffin–Lowry syndrome No cranial malformations
Colour vision Colour blindness
Normal clotting factor Haemophilia A & B
Strong muscle tissue Duchenne muscular dystrophy
fragile X syndrome Normal X chromosome
Aicardi syndrome Absence of brain defects
Absence of autoimmunity IPEX syndrome
Xg blood type Absence of antigen
Production of GAGs Hunter syndrome
Normal muscle strength Becker's Muscular Dystrophy
Unaffected body Fabry's disease
No progressive blindness Choroideremia
No kidney damage Dent's disease
Rett syndrome No microcephaly
Production of HGPRT Lesch–Nyhan syndrome
High levels of copper Menkes disease
Normal immune levels Wiskott–Aldrich syndrome
Focal dermal hypoplasia Normal pigmented skin
Normal pigment in eyes Ocular albinism
Vitamin D resistant rickets Absorption of Vitamin D
Synesthesia Non colour perception

Human traits with possible monogenic or oligogenic inheritance patterns

Dominant Recessive References
Low heart rate High heart rate [5]
Widow's peak straight hair line [6][7]
ocular hypertelorism Hypotelorism
Normal digestive muscle POLIP syndrome
Facial dimples * No facial dimples [8][9]
Able to taste PTC Unable to taste PTC [10]
Unattached (free) earlobe Attached earlobe [8][11][12]
Clockwise hair direction (left to right) Counter-Clockwise hair direction (right to left) [13]
Cleft chin smooth chin [14]
No progressive nerve damage Friedreich's ataxia
Ability to roll tongue (Able to hold tongue in a U shape) No ability to roll tongue
extra finger or toe Normal five fingers and toes
Straight Thumb Hitchhiker's Thumb
Freckles No freckles [8][15]
Wet-type earwax Dry-type earwax [11][16]
Normal flat palm Cenani Lenz syndactylism
shortness in fingers Normal finger length
Webbed fingers Normal separated fingers
Roman nose No prominent bridge [17]
Marfan's syndrome Normal body proportions [18]
Huntington's disease No nerve damage [19]
Normal mucus lining Cystic fibrosis [20]
Photic sneeze reflex No ACHOO reflex [21]
Forged chin Receding chin [17]
White Forelock Dark Forelock [22]
Ligamentous angustus Ligamentous Laxity [23]
Ability to eat sugar Galactosemia [24]
Total leukonychia and Bart pumphrey syndrome partial leukonychia [25]
Absence of fish-like body odour Trimethylaminuria [26]
Primary Hyperhidrosis little sweating in hands [27]
Lactose persistence * Lactose intolerance * [28]
Prominent chin (V-shaped) less prominent chin (U-shaped) [29]
Acne prone Clear complexion [30]
Normal height Cartilage–hair hypoplasia

Disabling conditions

Genetic
Chromosomal

Effect Source References
Down syndrome Additional 21st chromosome [31]
Cri du chat syndrome Partial deletion of a chromosome in the B Group [32]
Klinefelter syndrome One or more extra sex chromosome(s) [33]
Turner syndrome Rearrangement of one or both X chromosomes, deletion of part of the second X chromosome, presence of part of a Y chromosome [34]

[35]

See also

References

  1. ^ a b c d Nussbaum, Robert L.; McInnes, Roderick R.; Willard, Huntington F. (2007). Genetics in Medicine (7th ed.). Philadelphia: Saunders.
  2. ^ "Glossary". Genetics Home Reference. U.S. National Library of Medicine. 14 March 2008.
  3. ^ Freeman, Scott; Jon C., Herron (2007). "Evolutionary Analysis" (4th ed.). Upper Saddle River: Pearson:Prentice Hall.
  4. ^ a b Ahn, J.; Lee, J. (2008). "X Chromosome Inactivation". SciTable. Nature Education.
  5. ^ Calkins, Hugh. "Can Sinus Bradycardia Be Inherited?". NEJM Journal Watch. Massachusetts Medical Society.
  6. ^ Campbell, Neil; Reece, Jane (2005). Biology. San Francisco: Benjamin Cummings. p. 265. ISBN 0-07-366175-9.
  7. ^ McKusick, Victor A. (10 February 2009). . Online Mendelian Inheritance in Man. Johns Hopkins University. 194000. Archived from the original on 9 December 2015.
  8. ^ a b c . ScienceNet – Life Science. Singapore Science Centre. Archived from the original on 2003-09-25.
  9. ^ McKusick, Victor A. (25 June 1994). . Online Mendelian Inheritance in Man. Johns Hopkins University. 126100. Archived from the original on 9 April 2019.
  10. ^ Wooding, Stephen (28 June 2004). "Natural selection at work in genetic variation to taste". Medical News Today. from the original on 2007-12-13.
  11. ^ a b 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.
  12. ^ McKusick, Victor A.; Lopez, A (30 July 2010). "Earlobe Attachment, Attached vs. Unattached". Online Mendelian Inheritance in Man. Johns Hopkins University. 128900.[permanent dead link]
  13. ^ McDonald, John H. (8 December 2011). "Hair Whorl". Myths of Human Genetics. University of Delaware.
  14. ^ McKusick, Victor A. (23 March 2013). . Online Mendelian Inheritance in Man. Johns Hopkins University. 119000. Archived from the original on 29 April 2017.
  15. ^ 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.
  16. ^ McKusick, Victor A.; O'Neill, Marla J. F. (22 November 2010). . Online Mendelian Inheritance in Man. Johns Hopkins University. 117800. Archived from the original on 30 April 2017.
  17. ^ a b "Mendelian Traits in Humans" (PDF). Human Genetics. San Diego Supercomputer Center (SDSC).
  18. ^ Chen, Harold (2019-03-08). Buehler, Bruce (ed.). "Genetics of Marfan Syndrome". Medscape. WebMD LLC.
  19. ^ Stafford, Kate; Mannor, Michael. . Genetic Diseases. ThinkQuest. Archived from the original on 2007-01-03.
  20. ^ . Medical Genetics. Children's Hospital of Pittsburgh. 3 February 2008. Archived from the original on 24 August 2009. Retrieved 28 September 2011.
  21. ^ Schrock, Karen (10 January 2008). "Looking at the Sun Can Trigger a Sneeze". Scientific American. from the original on 2011-03-19.
  22. ^ "Inherited Human Traits". EdQuest. from the original on 2012-02-01.
  23. ^ 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.
  24. ^ Fankhauser, D. B. (2 Feb 2006). . University of Cincinnati Clermont College. Archived from the original on 2012-02-23.
  25. ^ Tüzün, Yalçın; Karaku, Özge (2009). (PDF). Journal of the Turkish Academy of Dermatology. JTAD. Archived from the original (PDF) on 2016-03-03. Retrieved 2012-03-03.
  26. ^ "Learning About Trimethylaminuria". genome.gov. National Human Genome Research Institute.
  27. ^ Kaufmann, Horacio; et al. (April 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.
  28. ^ Bowen, R. (25 April 2009). "Lactose Intolerance (Lactase Non-Persistence)". Colorado State University.
  29. ^ Jablecki, Donna Mae. "Variations on a Human Face" (PDF). Science Experiments on File. Facts on File.
  30. ^ Strickland, Barbara. . Sage Advice. Barbara Strickland. Archived from the original on 2006-02-07.
  31. ^ "Down Syndrome". Mosby's Dictionary of Medicine, Nursing & Health Professions. Elsevier Health Sciences. Retrieved 27 September 2013.
  32. ^ "Cri Du Chat Syndrome (Cat Cry Syndrome)". Encyclopedia of Special Education. Wiley. Retrieved 27 September 2013.
  33. ^ "Klinefelter Syndrome". Encyclopedia of Special Education. Wiley. Retrieved 27 September 2013.
  34. ^ Tager-Flusberg, Helen (1999). Neurodevelopmental Disorders. Massachusetts: Massachusetts Institute of Technology. p. 227. ISBN 0-262-20116-X.
  35. ^ "Etiology". Encyclopedia of Special Education. Wiley. Retrieved 27 September 2013.

Further reading

  • Speicher, Michael R.; Antonarakis, Stylianos E.; Motulsky, Arno G., eds. (2010). Vogel and Motulsky's Human Genetics: Problems and Approaches. Heidelberg: Springer Scientific. doi:10.1007/978-3-540-37654-5. ISBN 978-3-540-37653-8.
  • *Plomin, Robert; DeFries, John C.; Knopik, Valerie S.; Neiderhiser, Jenae M. (24 September 2012). Behavioral Genetics. Shaun Purcell (Appendix: Statistical Methods in Behavioral Genetics). Worth Publishers. ISBN 978-1-4292-4215-8. Retrieved 4 September 2013.
  • Flint, Jonathan; Greenspan, Ralph J.; Kendler, Kenneth S. (28 January 2010). How Genes Influence Behavior. Oxford University Press. ISBN 978-0-19-955990-9.
    • Lay summary in: Debby Tsuang; Andrew David (June 2011). "How Genes Influence Behavior". The American Journal of Psychiatry (Review). 168 (6): 656–657. doi:10.1176/appi.ajp.2011.11010097.
  • Gluckman, Peter; Beedle, Alan; Hanson, Mark (2009). Principles of Evolutionary Medicine. Oxford: Oxford University Press. ISBN 978-0-19-923639-8.
  • Hamilton, Matthew B. (2009). Population Genetics. Wiley-Blackwell. ISBN 978-1-4051-3277-0.
  • Moore, David S. (2003). The Dependent Gene: The Fallacy of "Nature vs. Nurture". New York: Macmillan. ISBN 978-0-8050-7280-8.
    • Lay summary in: Susan M Schneider (Spring 2007). "The Tangled Tale of Genes and Environment: Moore's The Dependent Gene: The Fallacy of "nature VS. Nurture"". Behav Anal. (Review). 30 (1): 91–105. PMC 2223161.
  • Cummings, Michael (1 January 2013). Human Heredity: Principles and Issues (10th ed.). Cengage Learning. ISBN 978-1-133-10687-6.

External links

  • How many Genes do humans have?
  • (website critique)
  • MITOMAP A human mitochondrial genome database

human, genetics, human, genetics, redirects, here, journal, human, genetics, journal, technical, introduction, topic, introduction, genetics, study, inheritance, occurs, human, beings, encompasses, variety, overlapping, fields, including, classical, genetics, . Human Genetics redirects here For the journal see Human Genetics journal For a non technical introduction to the topic see Introduction to genetics 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 Genes are the common factor of the qualities of most human inherited traits Study of human genetics can answer questions about human nature can help understand diseases and the development of effective treatment and help us to understand the genetics of human life This article describes only basic features of human genetics for the genetics of disorders please see medical genetics Representation of the double helix structure of human DNA Contents 1 Genetic differences and inheritance patterns 1 1 Autosomal dominant inheritance 1 2 Autosomal recessive inheritance 1 3 X linked and Y linked inheritance 1 4 Pedigrees analysis 1 5 Karyotype 2 Genomics 3 Medical genetics 4 Population genetics 5 Mitochondrial DNA 5 1 Genes and sex 5 2 X linked traits 5 3 Human traits with possible monogenic or oligogenic inheritance patterns 5 4 Disabling conditions 6 See also 7 References 8 Further reading 9 External linksGenetic differences and inheritance patterns Edit Autosomal dominant pattern a 50 50 chance Inheritance of traits for humans are based upon Gregor Mendel s model of inheritance Mendel deduced that inheritance depends upon discrete units of inheritance called factors or genes 1 Autosomal dominant inheritance Edit Autosomal traits are associated with a single gene on an autosome non sex chromosome they are called dominant because a single copy inherited from either parent is enough to cause this trait to appear This often means that one of the parents must also have the same trait unless it has arisen due to an unlikely new mutation Examples of autosomal dominant traits and disorders are Huntington s disease and achondroplasia Autosomal recessive inheritance Edit Autosomal recessive inheritance a 25 chance Autosomal recessive traits is one pattern of inheritance for a trait disease or disorder to be passed on through families For a recessive trait or disease to be displayed two copies of the trait or disorder needs to be presented The trait or gene will be located on a non sex chromosome Because it takes two copies of a trait to display a trait many people can unknowingly be carriers of a disease From an evolutionary perspective a recessive disease or trait can remain hidden for several generations before displaying the phenotype Examples of autosomal recessive disorders are albinism cystic fibrosis X linked and Y linked inheritance Edit X linked genes are found on the sex X chromosome X linked genes just like autosomal genes have both dominant and recessive types Recessive X linked disorders are rarely seen in females and usually only affect males This is because males inherit their X chromosome and all X linked genes will be inherited from the maternal side Fathers only pass on their Y chromosome to their sons so no X linked traits will be inherited from father to son Men cannot be carriers for recessive X linked traits as they only have one X chromosome so any X linked trait inherited from the mother will show up Females express X linked disorders when they are homozygous for the disorder and become carriers when they are heterozygous X linked dominant inheritance will show the same phenotype as a heterozygote and homozygote Just like X linked inheritance there will be a lack of male to male inheritance which makes it distinguishable from autosomal traits One example of an X linked trait is Coffin Lowry syndrome which is caused by a mutation in ribosomal protein gene This mutation results in skeletal craniofacial abnormalities mental retardation and short stature X chromosomes in females undergo a process known as X inactivation X inactivation is when one of the two X chromosomes in females is almost completely inactivated It is important that this process occurs otherwise a woman would produce twice the amount of normal X chromosome proteins The mechanism for X inactivation will occur during the embryonic stage For people with disorders like trisomy X where the genotype has three X chromosomes X inactivation will inactivate all X chromosomes until there is only one X chromosome active Males with Klinefelter syndrome who have an extra X chromosome will also undergo X inactivation to have only one completely active X chromosome Y linked inheritance occurs when a gene trait or disorder is transferred through the Y chromosome Since Y chromosomes can only be found in males Y linked traits are only passed on from father to son The testis determining factor which is located on the Y chromosome determines the maleness of individuals Besides the maleness inherited in the Y chromosome there are no other found Y linked characteristics Pedigrees analysis Edit An example of a family pedigree displaying an autosomal recessive trait A pedigree is a diagram showing the ancestral relationships and transmission of genetic traits over several generations in a family Square symbols are almost always used to represent males whilst circles are used for females Pedigrees are used to help detect many different genetic diseases A pedigree can also be used to help determine the chances for a parent to produce an offspring with a specific trait Four different traits can be identified by pedigree chart analysis autosomal dominant autosomal recessive x linked or y linked Partial penetrance can be shown and calculated from pedigrees Penetrance is the percentage expressed frequency with which individuals of a given genotype manifest at least some degree of a specific mutant phenotype associated with a trait Inbreeding or mating between closely related organisms can clearly be seen on pedigree charts Pedigree charts of royal families often have a high degree of inbreeding because it was customary and preferable for royalty to marry another member of royalty Genetic counselors commonly use pedigrees to help couples determine if the parents will be able to produce healthy children Karyotype Edit Micrographic karyogram of a human male showing 46 chromosomes including XY sex chromosomes Schematic karyogram of a human with annotated bands and sub bands It shows dark and white regions on G banding It shows 22 homologous chromosomes both the male XY and female XX versions of the sex chromosome bottom right as well as the mitochondrial genome at bottom left Further information Karyotype A karyotype is a very useful tool in cytogenetics A karyotype is picture of all the chromosomes in the metaphase stage arranged according to length and centromere position A karyotype can also be useful in clinical genetics due to its ability to diagnose genetic disorders On a normal karyotype aneuploidy can be detected by clearly being able to observe any missing or extra chromosomes 1 Giemsa banding g banding of the karyotype can be used to detect deletions insertions duplications inversions and translocations G banding will stain the chromosomes with light and dark bands unique to each chromosome A FISH fluorescent in situ hybridization can be used to observe deletions insertions and translocations FISH uses fluorescent probes to bind to specific sequences of the chromosomes that will cause the chromosomes to fluoresce a unique color 1 Genomics EditMain article Genomics Genomics is the field of genetics concerned with structural and functional studies of the genome 1 A genome is all the DNA contained within an organism or a cell including nuclear and mitochondrial DNA The human genome is the total collection of genes in a human being contained in the human chromosome composed of over three billion nucleotides 2 In April 2003 the Human Genome Project was able to sequence all the DNA in the human genome and to discover that the human genome was composed of around 20 000 protein coding genes Medical genetics EditMain article Medical genetics Medical genetics is the branch of medicine that involves the diagnosis and management of hereditary disorders Medical genetics is the application of genetics to medical care It overlaps human genetics for example research on the causes and inheritance of genetic disorders would be considered within both human genetics and medical genetics while the diagnosis management and counseling of individuals with genetic disorders would be considered part of medical genetics Population genetics EditMain article Population genetics Population genetics is the branch of evolutionary biology responsible for investigating processes that cause changes in allele and genotype frequencies in populations based upon Mendelian inheritance 3 Four different forces can influence the frequencies natural selection mutation gene flow migration and genetic drift A population can be defined as a group of interbreeding individuals and their offspring For human genetics the populations will consist only of the human species The Hardy Weinberg principle is a widely used principle to determine allelic and genotype frequencies Mitochondrial DNA EditIn addition to nuclear DNA humans like almost all eukaryotes have mitochondrial DNA Mitochondria the power houses of a cell have their own DNA Mitochondria are inherited from one s mother and their DNA is frequently used to trace maternal lines of descent see mitochondrial Eve Mitochondrial DNA is only 16kb in length and encodes for 62 genes XY Chromosomes Genes and sex Edit Main article XY sex determination system The XY sex determination system is the sex determination system found in humans most other mammals some insects Drosophila and some plants Ginkgo In this system the sex of an individual is determined by a pair of sex chromosomes gonosomes Females have two of the same kind of sex chromosome XX and are called the homogametic sex Males have two distinct sex chromosomes XY and are called the heterogametic sex X linked traits Edit Main article Sex linkage Sex linkage is the phenotypic expression of an allele related to the chromosomal sex of the individual This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes where both sexes have the same probability of inheritance Since humans have many more genes on the X than the Y there are many more X linked traits than Y linked traits However females carry two or more copies of the X chromosome resulting in a potentially toxic dose ofX linked genes 4 To correct this imbalance mammalian females have evolved a unique mechanism of dosage compensation In particular by way of the process called X chromosome inactivation XCI female mammals transcriptionally silence one of their two Xs in a complex and highly coordinated manner 4 X link dominant X link recessive ReferencesAlport syndrome Absence of blood in urineCoffin Lowry syndrome No cranial malformationsColour vision Colour blindnessNormal clotting factor Haemophilia A amp BStrong muscle tissue Duchenne muscular dystrophyfragile X syndrome Normal X chromosomeAicardi syndrome Absence of brain defectsAbsence of autoimmunity IPEX syndromeXg blood type Absence of antigenProduction of GAGs Hunter syndromeNormal muscle strength Becker s Muscular DystrophyUnaffected body Fabry s diseaseNo progressive blindness ChoroideremiaNo kidney damage Dent s diseaseRett syndrome No microcephalyProduction of HGPRT Lesch Nyhan syndromeHigh levels of copper Menkes diseaseNormal immune levels Wiskott Aldrich syndromeFocal dermal hypoplasia Normal pigmented skinNormal pigment in eyes Ocular albinismVitamin D resistant rickets Absorption of Vitamin DSynesthesia Non colour perceptionHuman traits with possible monogenic or oligogenic inheritance patterns Edit Main article List of Mendelian traits in humans Dominant Recessive ReferencesLow heart rate High heart rate 5 Widow s peak straight hair line 6 7 ocular hypertelorism HypotelorismNormal digestive muscle POLIP syndromeFacial dimples No facial dimples 8 9 Able to taste PTC Unable to taste PTC 10 Unattached free earlobe Attached earlobe 8 11 12 Clockwise hair direction left to right Counter Clockwise hair direction right to left 13 Cleft chin smooth chin 14 No progressive nerve damage Friedreich s ataxiaAbility to roll tongue Able to hold tongue in a U shape No ability to roll tongueextra finger or toe Normal five fingers and toesStraight Thumb Hitchhiker s ThumbFreckles No freckles 8 15 Wet type earwax Dry type earwax 11 16 Normal flat palm Cenani Lenz syndactylismshortness in fingers Normal finger lengthWebbed fingers Normal separated fingersRoman nose No prominent bridge 17 Marfan s syndrome Normal body proportions 18 Huntington s disease No nerve damage 19 Normal mucus lining Cystic fibrosis 20 Photic sneeze reflex No ACHOO reflex 21 Forged chin Receding chin 17 White Forelock Dark Forelock 22 Ligamentous angustus Ligamentous Laxity 23 Ability to eat sugar Galactosemia 24 Total leukonychia and Bart pumphrey syndrome partial leukonychia 25 Absence of fish like body odour Trimethylaminuria 26 Primary Hyperhidrosis little sweating in hands 27 Lactose persistence Lactose intolerance 28 Prominent chin V shaped less prominent chin U shaped 29 Acne prone Clear complexion 30 Normal height Cartilage hair hypoplasiaDisabling conditions Edit GeneticChromosomal Effect Source ReferencesDown syndrome Additional 21st chromosome 31 Cri du chat syndrome Partial deletion of a chromosome in the B Group 32 Klinefelter syndrome One or more extra sex chromosome s 33 Turner syndrome Rearrangement of one or both X chromosomes deletion of part of the second X chromosome presence of part of a Y chromosome 34 35 See also EditHuman evolutionary genetics Human genome List of Mendelian traits in humans Johns Hopkins Human Genetics ProgramReferences Edit a b c d Nussbaum Robert L McInnes Roderick R Willard Huntington F 2007 Genetics in Medicine 7th ed Philadelphia Saunders Glossary Genetics Home Reference U S National Library of Medicine 14 March 2008 Freeman Scott Jon C Herron 2007 Evolutionary Analysis 4th ed Upper Saddle River Pearson Prentice Hall a b Ahn J Lee J 2008 X Chromosome Inactivation SciTable Nature Education Calkins Hugh Can Sinus Bradycardia Be Inherited NEJM Journal Watch Massachusetts Medical Society Campbell Neil Reece Jane 2005 Biology San Francisco Benjamin Cummings p 265 ISBN 0 07 366175 9 McKusick Victor A 10 February 2009 Widow s Peak Online Mendelian Inheritance in Man Johns Hopkins University 194000 Archived from the original on 9 December 2015 a b c Genetics Reproduction ScienceNet Life Science Singapore Science Centre Archived from the original on 2003 09 25 McKusick Victor A 25 June 1994 Dimples Facial Online Mendelian Inheritance in Man Johns Hopkins University 126100 Archived from the original on 9 April 2019 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 a b 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 McKusick Victor A Lopez A 30 July 2010 Earlobe Attachment Attached vs Unattached Online Mendelian Inheritance in Man Johns Hopkins University 128900 permanent dead link McDonald John H 8 December 2011 Hair Whorl Myths of Human Genetics University of Delaware McKusick Victor A 23 March 2013 Cleft Chin Online Mendelian Inheritance in Man Johns Hopkins University 119000 Archived from the original on 29 April 2017 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 McKusick Victor A O Neill Marla J F 22 November 2010 Apocrine Gland Secretion Variation in Online 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Fankhauser D B 2 Feb 2006 Human Heritable Traits University of Cincinnati Clermont College Archived from the original on 2012 02 23 Tuzun Yalcin Karaku Ozge 2009 Leukonychia PDF Journal of the Turkish Academy of Dermatology JTAD Archived from the original PDF on 2016 03 03 Retrieved 2012 03 03 Learning About Trimethylaminuria genome gov National Human Genome Research Institute Kaufmann Horacio et al April 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 Bowen R 25 April 2009 Lactose Intolerance Lactase Non Persistence Colorado State University Jablecki Donna Mae Variations on a Human Face PDF Science Experiments on File Facts on File Strickland Barbara Acne is a Four Letter Word Sage Advice Barbara Strickland Archived from the original on 2006 02 07 Down Syndrome Mosby s Dictionary of Medicine Nursing amp Health Professions Elsevier Health Sciences Retrieved 27 September 2013 Cri Du Chat Syndrome Cat Cry Syndrome Encyclopedia of Special Education Wiley Retrieved 27 September 2013 Klinefelter Syndrome Encyclopedia of Special Education Wiley Retrieved 27 September 2013 Tager Flusberg Helen 1999 Neurodevelopmental Disorders Massachusetts Massachusetts Institute of Technology p 227 ISBN 0 262 20116 X Etiology Encyclopedia of Special Education Wiley Retrieved 27 September 2013 Further reading EditSpeicher Michael R Antonarakis Stylianos E Motulsky Arno G eds 2010 Vogel and Motulsky s Human Genetics Problems and Approaches Heidelberg Springer Scientific doi 10 1007 978 3 540 37654 5 ISBN 978 3 540 37653 8 Plomin Robert DeFries John C Knopik Valerie S Neiderhiser Jenae M 24 September 2012 Behavioral Genetics Shaun Purcell Appendix Statistical Methods in Behavioral Genetics Worth Publishers ISBN 978 1 4292 4215 8 Retrieved 4 September 2013 Flint Jonathan Greenspan Ralph J Kendler Kenneth S 28 January 2010 How Genes Influence Behavior Oxford University Press ISBN 978 0 19 955990 9 Lay summary in Debby Tsuang Andrew David June 2011 How Genes Influence Behavior The American Journal of Psychiatry Review 168 6 656 657 doi 10 1176 appi ajp 2011 11010097 Gluckman Peter Beedle Alan Hanson Mark 2009 Principles of Evolutionary Medicine Oxford Oxford University Press ISBN 978 0 19 923639 8 Hamilton Matthew B 2009 Population Genetics Wiley Blackwell ISBN 978 1 4051 3277 0 Moore David S 2003 The Dependent Gene The Fallacy of Nature vs Nurture New York Macmillan ISBN 978 0 8050 7280 8 Lay summary in Susan M Schneider Spring 2007 The Tangled Tale of Genes and Environment Moore s The Dependent Gene The Fallacy of nature VS Nurture Behav Anal Review 30 1 91 105 PMC 2223161 Cummings Michael 1 January 2013 Human Heredity Principles and Issues 10th ed Cengage Learning ISBN 978 1 133 10687 6 External links EditHuman Genome Project How many Genes do humans have Human Genetics Video website critique MITOMAP A human mitochondrial genome database 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