genetic factors
Both environmental and genetic factors have roles in the development of any disease. A genetic disorder is a disease caused by abnormalities in an individual’s genetic material (genome). The four different types of genetic disorders are(1) single-gene, (2) multifactorial, (3) chromosomal, and (4) mitochondrial.
genes
Genes generally express their functional effect through the production of proteins, which are complex molecules responsible for most functions in the cell. Proteins are chains of amino acids, and the DNA sequence of a gene (through RNA intermediate) is used to produce a specific protein sequence. This process begins with the production of an RNA molecule with a sequence matching the gene's DNA sequence, a process called transcription.
authors
^ Griffiths et al. (2000), Chapter 1 (Genetics and the Organism): Introduction
^ Hartl D, Jones E (2005)
^ Weiling F (1991). "Historical study: Johann Gregor Mendel 1822–1884". American Journal of Medical Genetics 40 (1): 1–25; discussion 26. doi:10.1002/ajmg.1320400103. PMID 1887835.
^ Lamarck, J-B (2008). In Encyclopædia Britannica. Retrieved from Encyclopædia Britannica Online on 2008-03-16.
^ a b Mendel, GJ (1866). "Versuche über Pflanzen-Hybriden". Verhandlungen des naturforschenden Vereins Brünn 4: 3–47. (in English in 1901, J. R. Hortic. Soc. 26: 1–32) translation available online
^ genetics, n., Oxford English Dictionary, 3rd ed.
^ Bateson W. Letter from William Bateson to Alan Sedgwick in 1905. The John Innes Centre. Retrieved on 2008-03-15.
^ genetic, adj., Oxford English Dictionary, 3rd ed.
^ Bateson, W (1907). "The Progress of Genetic Research". Wilks, W (editor) Report of the Third 1906 International Conference on Genetics: Hybridization (the cross-breeding of genera or species), the cross-breeding of varieties, and general plant breeding, London: Royal Horticultural Society.
Although the conference was titled "International Conference on Hybridisation and Plant Breeding", Wilks changed the title for publication as a result of Bateson's speech.
^ Moore JA (1983). "Thomas Hunt Morgan—The Geneticist". American Zoologist 23 (4): 855–865. doi:10.1093/icb/23.4.855.
^ Sturtevant AH (1913). "The linear arrangement of six sex-linked factors in Drosophila, as shown by their mode of association". Journal of Experimental Biology 14: 43–59. pdf from Electronic Scholarly Publishing
^ Avery OT, MacLeod CM, and McCarty M (1944). "Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III". Journal of Experimental Medicine 79 (1): 137–158. doi:10.1084/jem.79.2.137. 35th anniversary reprint available
^ Hershey AD, Chase M (1952). "Independent functions of viral protein and nucleic acid in growth of bacteriophage". The Journal of General Physiology 36: 39–56. doi:10.1085/jgp.36.1.39. PMID 12981234.
^ Judson, Horace (1979). The Eighth Day of Creation: Makers of the Revolution in Biology. Cold Spring Harbor Laboratory Press, 51–169. ISBN 0-87969-477-7.
^ Watson JD, Crick FHC (1953). "Molecular structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid" (PDF). Nature 171 (4356): 737–738. doi:10.1038/171737a0.
^ Watson JD, Crick FHC (1953). "Genetical Implications of the Structure of Deoxyribonucleic Acid" (PDF). Nature 171 (4361): 964–967. doi:10.1038/171964b0.
^ Sanger F, Nicklen S, and Coulson AR (1977). "DNA sequencing with chain-terminating inhibitors". Nature 74 (12): 5463–5467. doi:10.1073/pnas.74.12.5463. PMID 271968.
^ Saiki RK, Scharf S, Faloona F, Mullis KB, Horn GT, Erlich HA, Arnheim N (1985). "Enzymatic Amplification of β-Globin Genomic Sequences and Restriction Site Analysis for Diagnosis of Sickle Cell Anemia". Science 230 (4732): 1350–1354. doi:10.1126/science.2999980. PMID 2999980.
^ a b Human Genome Project Information. Human Genome Project. Retrieved on 2008-03-15.
^ Griffiths et al. (2000), Chapter 2 (Patterns of Inheritance): Introduction
^ Griffiths et al. (2000), Chapter 2 (Patterns of Inheritance): Mendel's experiments
^ Griffiths et al. (2000), Chapter 3 (Chromosomal Basis of Heredity): Mendelian genetics in eukaryotic life cycles
^ Griffiths et al. (2000), Chapter 4 (Gene Interaction): Interactions between the alleles of one gene
^ Richard W. Cheney. Genetic Notation. Retrieved on 2008-03-18.
^ Griffiths et al. (2000), Chapter 2 (Patterns of Inheritance): Human Genetics
^ Griffiths et al. (2000), Chapter 4 (Gene Interaction): Gene interaction and modified dihybrid ratios
^ Mayeux R (2005). "Mapping the new frontier: complex genetic disorders". The Journal of Clinical Investigation 115 (6): 1404–1407. doi:10.1172/JCI25421. PMID 15931374.
^ Griffiths et al. (2000), Chapter 25 (Quantitative Genetics): Quantifying heritability
^ Luke A, Guo X, Adeyemo AA, Wilks R, Forrester T, Lowe W Jr, Comuzzie AG, Martin LJ, Zhu X, Rotimi CN, Cooper RS (2001). "Heritability of obesity-related traits among Nigerians, Jamaicans and US black people". Int J Obes Relat Metab Disord 25 (7): 1034–1041. doi:10.1038/sj.ijo.0801650. Abstract from NCBI
^ Pearson H (2006). "Genetics: what is a gene?". Nature 441 (7092): 398–401. doi:10.1038/441398a. PMID 16724031.
^ Prescott, L (1993). Microbiology. Wm. C. Brown Publishers. 0-697-01372-3.
^ Griffiths et al. (2000), Chapter 8 (The Structure and Replication of DNA): Mechanism of DNA Replication
^ Gregory SG et al. (2006). "The DNA sequence and biological annotation of human chromosome 1". Nature 441: 315–321. doi:10.1038/nature04727. free full text available
^ Alberts et al. (2002), DNA and chromosomes: Chromosomal DNA and Its Packaging in the Chromatin Fiber
^ a b Griffiths et al. (2000), Chapter 3 (Chromosomal Basis of Heredity): Mendelian genetics in eukaryotic life cycles
^ Griffiths et al. (2000), Chapter 2 (Patterns of Inheritance): Sex chromosomes and sex-linked inheritance
^ Griffiths et al. (2000), Chapter 7 (Gene Transfer in Bacteria and Their Viruses): Bacterial conjugation
^ Griffiths et al. (2000), Chapter 7 (Gene Transfer in Bacteria and Their Viruses): Bacterial transformation
^ Griffiths et al. (2000), Chapter 5 (Basic Eukaryotic Chromosome Mapping): Nature of crossing-over
^ Griffiths et al. (2000), Chapter 5 (Basic Eukaryotic Chromosome Mapping): Linkage maps
^ Berg JM, Tymoczko JL, Stryer L, Clarke ND (2002). Biochemistry, 5th edition, New York: W. H. Freeman and Company. I. 5. DNA, RNA, and the Flow of Genetic Information: Amino Acids Are Encoded by Groups of Three Bases Starting from a Fixed Point
^ Crick, F (1970): Central Dogma of Molecular Biology (PDF). Nature 227, 561–563. PMID 4913914
^ Alberts et al. (2002), Proteins: The Shape and Structure of Proteins
^ Alberts et al. (2002), Proteins: Protein Function
^ How Does Sickle Cell Cause Disease?. Brigham and Women's Hospital: Information Center for Sickle Cell and Thalassemic Disorders (2002-04-11). Retrieved on 2007-07-23.
^ Imes DL, Geary LA, Grahn RA, Lyons LA (2006). "Albinism in the domestic cat (Felis catus) is associated with a tyrosinase (TYR) mutation" (Short Communication). Animal Genetics 37 (2): 175. doi:10.1111/j.1365-2052.2005.01409.x. Retrieved on 2006-05-29.
^ MedlinePlus: Phenylketonuria. NIH: National Library of Medicine. Retrieved on 2008-03-15.
^ Brivanlou AH, Darnell JE Jr (2002). "Signal transduction and the control of gene expression". Science 295 (5556): 813–818. doi:10.1126/science.1066355. PMID 11823631.
^ Alberts et al. (2002), Control of Gene Expression - The Tryptophan Repressor Is a Simple Switch That Turns Genes On and Off in Bacteria
^ Jaenisch R, Bird A. "Epigenetic regulation of gene expression: how the genome integrates intrinsic and environmental signals". Nature Genetics 33 (3s): 245–254. doi:10.1038/ng1089.
^ Chandler VL (2007). "Paramutation: From Maize to Mice". Cell 128: 641–645. doi:10.1016/j.cell.2007.02.007.
^ Griffiths et al. (2000), Chapter 16 (Mechanisms of Gene Mutation): Spontaneous mutations
^ Kunkel TA (2004). "DNA Replication Fidelity". Journal of Biological Chemistry 279 (17): 16895–16898. doi:10.1038/sj.emboj.7600158.
^ Griffiths et al. (2000), Chapter 16 (Mechanisms of Gene Mutation): Induced mutations
^ Griffiths et al. (2000), Chapter 17 (Chromosome Mutation I: Changes in Chromosome Structure): Introduction
^ Griffiths et al. (2000), Chapter 24 (Population Genetics): Variation and its modulation
^ Griffiths et al. (2000), Chapter 24 (Population Genetics): Selection
^ Griffiths et al. (2000), Chapter 24 (Population Genetics): Random events
^ Darwin, Charles (1859). On the Origin of Species, 1st, John Murray, 1. . Related earlier ideas were acknowledged in Darwin, Charles (1861). On the Origin of Species, 3rd, John Murray, xiii.
^ Gavrilets S (2003). "Perspective: models of speciation: what have we learned in 40 years?". Evolution 57 (10): 2197–2215. doi:10.1554/02-727. PMID 14628909.
^ Wolf YI, Rogozin IB, Grishin NV, Koonin EV (2002). "Genome trees and the tree of life". Trends Genet. 18 (9): 472–479. doi:10.1016/S0168-9525(02)02744-0. PMID 12175808.
^ The Use of Model Organisms in Instruction. University of Wisconsin: Wisconsin Outreach Research Modules. Retrieved on 2008-03-15.
^ NCBI: Genes and Disease. NIH: National Center for Biotechnology Information. Retrieved on 2008-03-15.
^ Davey Smith, G; Ebrahim, S (2003). "‘Mendelian randomization’: can genetic epidemiology contribute to understanding environmental determinants of disease?". International Journal of Epidemiology 32: 1–22. doi:10.1093/ije/dyg070. PMID 12689998.
^ Pharmacogenetics Fact Sheet. NIH: National Institute of General Medical Sciences. Retrieved on 2008-03-15.
^ Strachan T, Read AP (1999). Human Molecular Genetics 2, second edition, John Wiley & Sons Inc.. Chapter 18: Cancer Genetics
^ Lodish et al. (2000), Chapter 7: 7.1. DNA Cloning with Plasmid Vectors
^ Lodish et al. (2000), Chapter 7: 7.7. Polymerase Chain Reaction: An Alternative to Cloning
^ Brown TA (2002). Genomes 2, 2nd edition. ISBN ISBN 1 85996 228 9. Section 2, Chapter 6: 6.1. The Methodology for DNA Sequencing
^ Brown (2002), Section 2, Chapter 6: 6.2. Assembly of a Contiguous DNA Sequence
^ Hartl D, Jones E (2005)
^ Weiling F (1991). "Historical study: Johann Gregor Mendel 1822–1884". American Journal of Medical Genetics 40 (1): 1–25; discussion 26. doi:10.1002/ajmg.1320400103. PMID 1887835.
^ Lamarck, J-B (2008). In Encyclopædia Britannica. Retrieved from Encyclopædia Britannica Online on 2008-03-16.
^ a b Mendel, GJ (1866). "Versuche über Pflanzen-Hybriden". Verhandlungen des naturforschenden Vereins Brünn 4: 3–47. (in English in 1901, J. R. Hortic. Soc. 26: 1–32) translation available online
^ genetics, n., Oxford English Dictionary, 3rd ed.
^ Bateson W. Letter from William Bateson to Alan Sedgwick in 1905. The John Innes Centre. Retrieved on 2008-03-15.
^ genetic, adj., Oxford English Dictionary, 3rd ed.
^ Bateson, W (1907). "The Progress of Genetic Research". Wilks, W (editor) Report of the Third 1906 International Conference on Genetics: Hybridization (the cross-breeding of genera or species), the cross-breeding of varieties, and general plant breeding, London: Royal Horticultural Society.
Although the conference was titled "International Conference on Hybridisation and Plant Breeding", Wilks changed the title for publication as a result of Bateson's speech.
^ Moore JA (1983). "Thomas Hunt Morgan—The Geneticist". American Zoologist 23 (4): 855–865. doi:10.1093/icb/23.4.855.
^ Sturtevant AH (1913). "The linear arrangement of six sex-linked factors in Drosophila, as shown by their mode of association". Journal of Experimental Biology 14: 43–59. pdf from Electronic Scholarly Publishing
^ Avery OT, MacLeod CM, and McCarty M (1944). "Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III". Journal of Experimental Medicine 79 (1): 137–158. doi:10.1084/jem.79.2.137. 35th anniversary reprint available
^ Hershey AD, Chase M (1952). "Independent functions of viral protein and nucleic acid in growth of bacteriophage". The Journal of General Physiology 36: 39–56. doi:10.1085/jgp.36.1.39. PMID 12981234.
^ Judson, Horace (1979). The Eighth Day of Creation: Makers of the Revolution in Biology. Cold Spring Harbor Laboratory Press, 51–169. ISBN 0-87969-477-7.
^ Watson JD, Crick FHC (1953). "Molecular structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid" (PDF). Nature 171 (4356): 737–738. doi:10.1038/171737a0.
^ Watson JD, Crick FHC (1953). "Genetical Implications of the Structure of Deoxyribonucleic Acid" (PDF). Nature 171 (4361): 964–967. doi:10.1038/171964b0.
^ Sanger F, Nicklen S, and Coulson AR (1977). "DNA sequencing with chain-terminating inhibitors". Nature 74 (12): 5463–5467. doi:10.1073/pnas.74.12.5463. PMID 271968.
^ Saiki RK, Scharf S, Faloona F, Mullis KB, Horn GT, Erlich HA, Arnheim N (1985). "Enzymatic Amplification of β-Globin Genomic Sequences and Restriction Site Analysis for Diagnosis of Sickle Cell Anemia". Science 230 (4732): 1350–1354. doi:10.1126/science.2999980. PMID 2999980.
^ a b Human Genome Project Information. Human Genome Project. Retrieved on 2008-03-15.
^ Griffiths et al. (2000), Chapter 2 (Patterns of Inheritance): Introduction
^ Griffiths et al. (2000), Chapter 2 (Patterns of Inheritance): Mendel's experiments
^ Griffiths et al. (2000), Chapter 3 (Chromosomal Basis of Heredity): Mendelian genetics in eukaryotic life cycles
^ Griffiths et al. (2000), Chapter 4 (Gene Interaction): Interactions between the alleles of one gene
^ Richard W. Cheney. Genetic Notation. Retrieved on 2008-03-18.
^ Griffiths et al. (2000), Chapter 2 (Patterns of Inheritance): Human Genetics
^ Griffiths et al. (2000), Chapter 4 (Gene Interaction): Gene interaction and modified dihybrid ratios
^ Mayeux R (2005). "Mapping the new frontier: complex genetic disorders". The Journal of Clinical Investigation 115 (6): 1404–1407. doi:10.1172/JCI25421. PMID 15931374.
^ Griffiths et al. (2000), Chapter 25 (Quantitative Genetics): Quantifying heritability
^ Luke A, Guo X, Adeyemo AA, Wilks R, Forrester T, Lowe W Jr, Comuzzie AG, Martin LJ, Zhu X, Rotimi CN, Cooper RS (2001). "Heritability of obesity-related traits among Nigerians, Jamaicans and US black people". Int J Obes Relat Metab Disord 25 (7): 1034–1041. doi:10.1038/sj.ijo.0801650. Abstract from NCBI
^ Pearson H (2006). "Genetics: what is a gene?". Nature 441 (7092): 398–401. doi:10.1038/441398a. PMID 16724031.
^ Prescott, L (1993). Microbiology. Wm. C. Brown Publishers. 0-697-01372-3.
^ Griffiths et al. (2000), Chapter 8 (The Structure and Replication of DNA): Mechanism of DNA Replication
^ Gregory SG et al. (2006). "The DNA sequence and biological annotation of human chromosome 1". Nature 441: 315–321. doi:10.1038/nature04727. free full text available
^ Alberts et al. (2002), DNA and chromosomes: Chromosomal DNA and Its Packaging in the Chromatin Fiber
^ a b Griffiths et al. (2000), Chapter 3 (Chromosomal Basis of Heredity): Mendelian genetics in eukaryotic life cycles
^ Griffiths et al. (2000), Chapter 2 (Patterns of Inheritance): Sex chromosomes and sex-linked inheritance
^ Griffiths et al. (2000), Chapter 7 (Gene Transfer in Bacteria and Their Viruses): Bacterial conjugation
^ Griffiths et al. (2000), Chapter 7 (Gene Transfer in Bacteria and Their Viruses): Bacterial transformation
^ Griffiths et al. (2000), Chapter 5 (Basic Eukaryotic Chromosome Mapping): Nature of crossing-over
^ Griffiths et al. (2000), Chapter 5 (Basic Eukaryotic Chromosome Mapping): Linkage maps
^ Berg JM, Tymoczko JL, Stryer L, Clarke ND (2002). Biochemistry, 5th edition, New York: W. H. Freeman and Company. I. 5. DNA, RNA, and the Flow of Genetic Information: Amino Acids Are Encoded by Groups of Three Bases Starting from a Fixed Point
^ Crick, F (1970): Central Dogma of Molecular Biology (PDF). Nature 227, 561–563. PMID 4913914
^ Alberts et al. (2002), Proteins: The Shape and Structure of Proteins
^ Alberts et al. (2002), Proteins: Protein Function
^ How Does Sickle Cell Cause Disease?. Brigham and Women's Hospital: Information Center for Sickle Cell and Thalassemic Disorders (2002-04-11). Retrieved on 2007-07-23.
^ Imes DL, Geary LA, Grahn RA, Lyons LA (2006). "Albinism in the domestic cat (Felis catus) is associated with a tyrosinase (TYR) mutation" (Short Communication). Animal Genetics 37 (2): 175. doi:10.1111/j.1365-2052.2005.01409.x. Retrieved on 2006-05-29.
^ MedlinePlus: Phenylketonuria. NIH: National Library of Medicine. Retrieved on 2008-03-15.
^ Brivanlou AH, Darnell JE Jr (2002). "Signal transduction and the control of gene expression". Science 295 (5556): 813–818. doi:10.1126/science.1066355. PMID 11823631.
^ Alberts et al. (2002), Control of Gene Expression - The Tryptophan Repressor Is a Simple Switch That Turns Genes On and Off in Bacteria
^ Jaenisch R, Bird A. "Epigenetic regulation of gene expression: how the genome integrates intrinsic and environmental signals". Nature Genetics 33 (3s): 245–254. doi:10.1038/ng1089.
^ Chandler VL (2007). "Paramutation: From Maize to Mice". Cell 128: 641–645. doi:10.1016/j.cell.2007.02.007.
^ Griffiths et al. (2000), Chapter 16 (Mechanisms of Gene Mutation): Spontaneous mutations
^ Kunkel TA (2004). "DNA Replication Fidelity". Journal of Biological Chemistry 279 (17): 16895–16898. doi:10.1038/sj.emboj.7600158.
^ Griffiths et al. (2000), Chapter 16 (Mechanisms of Gene Mutation): Induced mutations
^ Griffiths et al. (2000), Chapter 17 (Chromosome Mutation I: Changes in Chromosome Structure): Introduction
^ Griffiths et al. (2000), Chapter 24 (Population Genetics): Variation and its modulation
^ Griffiths et al. (2000), Chapter 24 (Population Genetics): Selection
^ Griffiths et al. (2000), Chapter 24 (Population Genetics): Random events
^ Darwin, Charles (1859). On the Origin of Species, 1st, John Murray, 1. . Related earlier ideas were acknowledged in Darwin, Charles (1861). On the Origin of Species, 3rd, John Murray, xiii.
^ Gavrilets S (2003). "Perspective: models of speciation: what have we learned in 40 years?". Evolution 57 (10): 2197–2215. doi:10.1554/02-727. PMID 14628909.
^ Wolf YI, Rogozin IB, Grishin NV, Koonin EV (2002). "Genome trees and the tree of life". Trends Genet. 18 (9): 472–479. doi:10.1016/S0168-9525(02)02744-0. PMID 12175808.
^ The Use of Model Organisms in Instruction. University of Wisconsin: Wisconsin Outreach Research Modules. Retrieved on 2008-03-15.
^ NCBI: Genes and Disease. NIH: National Center for Biotechnology Information. Retrieved on 2008-03-15.
^ Davey Smith, G; Ebrahim, S (2003). "‘Mendelian randomization’: can genetic epidemiology contribute to understanding environmental determinants of disease?". International Journal of Epidemiology 32: 1–22. doi:10.1093/ije/dyg070. PMID 12689998.
^ Pharmacogenetics Fact Sheet. NIH: National Institute of General Medical Sciences. Retrieved on 2008-03-15.
^ Strachan T, Read AP (1999). Human Molecular Genetics 2, second edition, John Wiley & Sons Inc.. Chapter 18: Cancer Genetics
^ Lodish et al. (2000), Chapter 7: 7.1. DNA Cloning with Plasmid Vectors
^ Lodish et al. (2000), Chapter 7: 7.7. Polymerase Chain Reaction: An Alternative to Cloning
^ Brown TA (2002). Genomes 2, 2nd edition. ISBN ISBN 1 85996 228 9. Section 2, Chapter 6: 6.1. The Methodology for DNA Sequencing
^ Brown (2002), Section 2, Chapter 6: 6.2. Assembly of a Contiguous DNA Sequence
References
Alberts B, Johnson A, Lewis J, Raff M, Roberts K, and Walter P (2002). Molecular Biology of the Cell, 4th edition. ISBN 0-8153-3218-1.
Griffiths AJF, Miller JH, Suzuki DT, Lewontin RC, and Gelbart WM (2000). An Introduction to Genetic Analysis. New York: W.H. Freeman and Company. ISBN 0-7167-3520-2.
Hartl D, Jones E (2005). Genetics: Analysis of Genes and Genomes, 6th edition. Jones & Bartlett. ISBN 0-7637-1511-5.
Lodish H, Berk A, Zipursky LS, Matsudaira P, Baltimore D, and Darnell J (2000). Molecular Cell Biology, 4th edition. ISBN 0-7167-3136-3.
articles
Main articles: Asexual reproduction and Sexual reproduction
When cells divide, their full genome is copied and each daughter cell inherits one copy. This process, called mitosis, is the simplest form of reproduction and is the basis for asexual reproduction. Asexual reproduction can also occur in multicellular organisms, producing offspring that inherit their genome from a single parent. Offspring that are genetically identical to their parents are called clones.
When cells divide, their full genome is copied and each daughter cell inherits one copy. This process, called mitosis, is the simplest form of reproduction and is the basis for asexual reproduction. Asexual reproduction can also occur in multicellular organisms, producing offspring that inherit their genome from a single parent. Offspring that are genetically identical to their parents are called clones.
Interactions of multiple genes
Human height is a complex genetic trait. Francis Galton's data from 1889 shows the relationship between offspring height as a function of mean parent height. While correlated, remaining variation in offspring heights indicates environment is also an important factor in this trait.
Organisms have thousands of genes, and in sexually reproducing organisms assortment of these genes are generally independent of each other. This means that the inheritance of an allele for yellow or green pea color is unrelated to the inheritance of alleles for white or purple flowers. This phenomenon, known as "Mendel's second law" or the "Law of independent assortment", means that the alleles of different genes get shuffled between parents to form offspring with many different combinations. (Some genes do not assort independently, demonstrating genetic linkage, a topic discussed later in this article.)
Often different genes can interact in a way that influences the same trait. In the Blue-eyed Mary (Omphalodes verna), for example, there exists a gene with alleles that determine the color of flowers: blue or magenta. Another gene, however, controls whether the flowers have color at all: color or white. When a plant has two copies of this white allele, its flowers are white—regardless of whether the first gene has blue or magenta alleles. This interaction between genes is called epistasis, with the second gene epistatic to the first.[26]
Many traits are not discrete features (eg. purple or white flowers) but are instead continuous features (eg. human height and skin color). These complex traits are the product of many genes.[27] The influence of these genes is mediated, to varying degrees, by the environment an organism has experienced. The degree to which an organism's genes contribute to a complex trait is called heritability.[28] Measurement of the heritability of a trait is relative—in a more variable environment, the environment has a bigger influence on the total variation of the trait. For example, human height is a complex trait with a heritability of 89% in the United States. In Nigeria, however, where people experience a more variable access to good nutrition and health care, height has a heritability of only 62%.[29]
Subscribe to:
Posts (Atom)