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Additive genetic effects

Additive genetic effects, discovered in 1910 by Nilsson-Ehle, are quantitative changes certain alleles, called additive alleles, cause in a phenotype regardless of any other alleles that are present or absent.^[1]^[2] Alleles for an additive trait often come from different loci, and contribute to the quantitative trait of an individual such that the phenotype is equal to the sum of the effects of individual alleles, or proportional to the number of alleles.^[1]^[3] The environment, however, also has an effect on individuals' phenotypes, such that the mean phenotype of all individuals with one genotype is dependent on the number of alleles, but individuals with the same genotype do not all have identical phenotypes.^[4]

Types of additive traits

There are three main types of additive traits: continuous traits, such as height that exist on a continuum;^[5] meristic traits, that fall into discrete classes (such as counts);^[6] and threshold traits, which are either present or absent depending on the number of additive alleles in the genotype.^[7]

Calculation of additive effects

Additive effects are often calculated by genotyping and phenotyping offspring of a genetic test cross. If there are two alleles at a gene locus then the additive effect is half of the difference between the mean of all cases that are homozygous for one version of the allele (a/a) compared to the mean of all cases that are homozygous for the other allele (A/A). Sometimes, however, the genotype cannot be directly determined, so it may be estimated using the individual’s breeding value: double the difference in mean phenotype between a population the individual is randomly mated to (multiple mates) and the the offspring produced.^[8]

Heritability, selection, and additive alleles

Additive genetic effects where there are several loci in the genome produce heritable variation in phenotype, and are thus responsible for parent-offspring resemblance.^[2] The variance in additive alleles in a population (denoted V_A) divided by the variance in phenotype in the population (denoted V_P) produces the proportion of phenotypic variance caused by additive genetic effects, called narrow-sense heritability, h².^[2]

This heritable variation between individuals in a population or species provides a basis for selection.^[9] Narrow-sense heritability (h²) is a predictor of a trait's response to selection; increased variance in phenotype (due to strong genetic effects) causes the rate of selection to increase.^[2]^[9]

References

^ ^a ^b Silson, R. G. (1988). Additive Genes in Evolution and Selection. Tring, Herts., England: Greenfield Publications
^ ^a ^b ^c ^d Freeman, S., Herron, J. C. (2007). Evolutionary Analysis (4th ed.). San Francisco, CA: Pearson Benjamin Cummings.
^ MedicineNet. Definition of Additive Genetic Effects. Last updated June 14, 2012. Retrieved November 1, 2014 from http://www.medicinenet.com/script/main/art.asp?articlekey=25508
^ 'The Distinction Between Innate and Acquired Characteristics. (2009). In Stanford Encyclopedia of Philosophy. Retrieved from: http://plato.stanford.edu/entries/innate-acquired/
^ Rédei, G. P. (2008). Continuous Trait. Encyclopedia of Genetics, Genomics, Proteomics, and Informatics. (Vol. 2, pp. 415). Netherlands: Springer.
^ Rédei, G. P. (2008). Meristic Traits. Encyclopedia of Genetics, Genomics, Proteomics, and Informatics. (Vol. 2, pp. 1186). Netherlands: Springer.
^ Rédei, G. P. (2008). Threshold Traits. Encyclopedia of Genetics, Genomics, Proteomics, and Informatics. (Vol. 2, pp. 1963). Netherlands: Springer.
^ Barton, N. H., Briggs, D. E. G., Eisen, J. A., Goldstein, D. B., Patel, N. H. (2010). Evolution. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.
^ ^a ^b Wolf, J. B., Brodie III, E. D., Cheverud, J. M., Moore, A. J., Wade, M. J. (1998). Evolutionary consequences of indirect genetic effects. Trends in Ecology and Evolution 13(2): 64-69. doi: 10.1016/S0169-5347(97)01233-0

This article was the subject of an educational assignment in 2014 Q3. Further details were available on the "Education Program:University of Western Ontario/Advanced Genetics (Fall 2014)" page, which is now unavailable on the wiki.

Additive genetic effects (currently a very short stub with no citations)

I haven't started researching articles on it yet, but I learned about it in Evolutionary Genetics last year so I have an idea of what I can add to it and where to start.

Rough Draft

Additive Genetic Effects

Additive genetic effects are when alleles from different loci, called additive alleles, contribute to the quantitative trait (see quantitative genetics) of an individual such that the phenotype is equal to the sum of the effects of individual alleles, or proportional to the number of alleles^[1]. The additive genetic effect of an allele is an estimate of the quantitative change in a trait that is associated with substituting one allele (one genotype) with that of another allele within an interbreeding population (this sentence is from the original stub).

Types of Additive Traits

Here I will talk about continuous additive traits, such as height that can be measured on a continuous scale, and meristic additive traits, which are discrete "counts" such as number of leaves.

Calculation of Additive Effects

Here I will paste the rest of the stub, talking about how additive effects are calculated from test crosses. It gives an example for how the additive effect of a trait controlled by one locus with two alleles is calculated, so I will see if I can find how more comlex traits are calculated if they are not too complicated for me to understand and for the purposes of this project.

Heritability and Additive Alleles

Here I will talk about heritable variation, and how a trait must be additive to be heritable.

^ MedicineNet. Definition of Additive Genetic Effects. Last updated June 14, 2012. Retrieved November 1, 2014 from http://www.medicinenet.com/script/main/art.asp?articlekey=25508

[x-1] Silson, R. G. (1988). Additive Genes in Evolution and Selection. Tring, Herts., England: Greenfield Publications

[y-2] Freeman, S., Herron, J. C. (2007). Evolutionary Analysis (4th ed.). San Francisco, CA: Pearson Benjamin Cummings.

[3] MedicineNet. Definition of Additive Genetic Effects. Last updated June 14, 2012. Retrieved November 1, 2014 from http://www.medicinenet.com/script/main/art.asp?articlekey=25508

[4] 'The Distinction Between Innate and Acquired Characteristics. (2009). In Stanford Encyclopedia of Philosophy. Retrieved from: http://plato.stanford.edu/entries/innate-acquired/

[5] Rédei, G. P. (2008). Continuous Trait. Encyclopedia of Genetics, Genomics, Proteomics, and Informatics. (Vol. 2, pp. 415). Netherlands: Springer.

[6] Rédei, G. P. (2008). Meristic Traits. Encyclopedia of Genetics, Genomics, Proteomics, and Informatics. (Vol. 2, pp. 1186). Netherlands: Springer.

[7] Rédei, G. P. (2008). Threshold Traits. Encyclopedia of Genetics, Genomics, Proteomics, and Informatics. (Vol. 2, pp. 1963). Netherlands: Springer.

[8] Barton, N. H., Briggs, D. E. G., Eisen, J. A., Goldstein, D. B., Patel, N. H. (2010). Evolution. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.

[z-9] Wolf, J. B., Brodie III, E. D., Cheverud, J. M., Moore, A. J., Wade, M. J. (1998). Evolutionary consequences of indirect genetic effects. Trends in Ecology and Evolution 13(2): 64-69. doi: 10.1016/S0169-5347(97)01233-0

[10] MedicineNet. Definition of Additive Genetic Effects. Last updated June 14, 2012. Retrieved November 1, 2014 from http://www.medicinenet.com/script/main/art.asp?articlekey=25508

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 <!-- EDIT BELOW THIS LINE -->
 ==Additive genetic effects==
-Additive genetic effects, discovered in 1910 by Nilsson-Ehle, are quantitative changes certain [[alleles]], called additive alleles, cause in a [[phenotype]] regardless of any other alleles that are present or absent<ref name=x>Silson, R. G. (1988). ''Additive Genes in Evolution and Selection''. Tring, Herts., England: Greenfield Publications</ref><ref name=y>Freeman, S., Herron, J. C. (2007). ''Evolutionary Analysis'' (4th ed.). San Francisco, CA: Pearson Benjamin Cummings.</ref>. Alleles for an additive [[trait]] often come from different [[loci]], and contribute to the quantitative trait (see [[quantitative genetics]]) of an individual such that the phenotype is equal to the sum of the effects of individual alleles, or proportional to the number of alleles<ref name=x /><ref>MedicineNet. ''Definition of Additive Genetic Effects''. Last updated June 14, 2012. Retrieved November 1, 2014 from http://www.medicinenet.com/script/main/art.asp?articlekey=25508</ref>. The [[environment]], however, also has an effect on phenotype, such that it is the ''mean'' phenotype for individuals with a genotype that is proportional to the number of alleles; individuals with the same [[genotype]] do not have identical phenotypes<ref>'The Distinction Between Innate and Acquired Characteristics. (2009). In ''Stanford Encyclopedia of Philosophy''. Retrieved from: http://plato.stanford.edu/entries/innate-acquired/</ref>.
+Additive genetic effects, discovered in 1910 by Nilsson-Ehle, are quantitative changes certain [[alleles]], called additive alleles, cause in a [[phenotype]] regardless of any other alleles that are present or absent.<ref name=x>Silson, R. G. (1988). ''Additive Genes in Evolution and Selection''. Tring, Herts., England: Greenfield Publications</ref><ref name=y>Freeman, S., Herron, J. C. (2007). ''Evolutionary Analysis'' (4th ed.). San Francisco, CA: Pearson Benjamin Cummings.</ref> Alleles for an additive [[trait]] often come from different [[loci]], and contribute to the [[Quantitative genetics|quantitative trait]] of an individual such that the phenotype is equal to the sum of the effects of individual alleles, or proportional to the number of alleles.<ref name=x /><ref>MedicineNet. ''Definition of Additive Genetic Effects''. Last updated June 14, 2012. Retrieved November 1, 2014 from http://www.medicinenet.com/script/main/art.asp?articlekey=25508</ref> The [[environment]], however, also has an effect on individuals' phenotypes, such that the [[mean]] phenotype of all individuals with one [[genotype]] is dependent on the number of alleles, but individuals with the same genotype do not all have identical phenotypes.<ref>'The Distinction Between Innate and Acquired Characteristics. (2009). In ''Stanford Encyclopedia of Philosophy''. Retrieved from: http://plato.stanford.edu/entries/innate-acquired/</ref>
 ==Types of additive traits==
-There are three main types of additive traits: continuous traits, such as height that exist on a continuum<ref>Rédei, G. P. (2008). Continuous Trait. ''Encyclopedia of Genetics, Genomics, Proteomics, and Informatics''. (Vol. 2, pp. 415). Netherlands: Springer.</ref>; meristic traits, that fall into discrete classes (such as counts)<ref>Rédei, G. P. (2008). Meristic Traits. ''Encyclopedia of Genetics, Genomics, Proteomics, and Informatics''. (Vol. 2, pp. 1186). Netherlands: Springer.</ref>; and threshold traits, which are either present or absent depending on the number of additive alleles in the genotype<ref>Rédei, G. P. (2008). Threshold Traits. ''Encyclopedia of Genetics, Genomics, Proteomics, and Informatics''. (Vol. 2, pp. 1963). Netherlands: Springer.</ref>.
+There are three main types of additive traits: continuous traits, such as height that exist on a continuum;<ref>Rédei, G. P. (2008). Continuous Trait. ''Encyclopedia of Genetics, Genomics, Proteomics, and Informatics''. (Vol. 2, pp. 415). Netherlands: Springer.</ref> meristic traits, that fall into discrete classes (such as counts);<ref>Rédei, G. P. (2008). Meristic Traits. ''Encyclopedia of Genetics, Genomics, Proteomics, and Informatics''. (Vol. 2, pp. 1186). Netherlands: Springer.</ref> and threshold traits, which are either present or absent depending on the number of additive alleles in the genotype.<ref>Rédei, G. P. (2008). Threshold Traits. ''Encyclopedia of Genetics, Genomics, Proteomics, and Informatics''. (Vol. 2, pp. 1963). Netherlands: Springer.</ref>
 ==Calculation of additive effects==
-'''Additive effects are often calculated by genotyping and phenotyping offspring of a genetic [[test cross]]. If there are two alleles at a [[gene locus]] then the additive effect is half of the difference between the mean of all cases that are [[homozygous]] for one version of the allele (a/a) compared to the mean of all cases that are homozygous for the other allele (A/A)'''. Sometimes, however, the genotype cannot be directly determined, so it may be estimated using the individual’s breeding value: double the difference in mean phenotype between a [[population]] the individual is randomly mated to (multiple mates) and the the offspring produced<ref>Barton, N. H., Briggs, D. E. G., Eisen, J. A., Goldstein, D. B., Patel, N. H. (2010). ''Evolution''. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.</ref>.
+'''Additive effects are often calculated by genotyping and phenotyping offspring of a genetic [[test cross]]. If there are two alleles at a [[gene locus]] then the additive effect is half of the difference between the mean of all cases that are [[homozygous]] for one version of the allele (a/a) compared to the mean of all cases that are homozygous for the other allele (A/A)'''. Sometimes, however, the genotype cannot be directly determined, so it may be estimated using the individual’s breeding value: double the difference in mean phenotype between a [[population]] the individual is randomly mated to (multiple mates) and the the offspring produced.<ref>Barton, N. H., Briggs, D. E. G., Eisen, J. A., Goldstein, D. B., Patel, N. H. (2010). ''Evolution''. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.</ref>
 ==Heritability, selection, and additive alleles==
-Additive genetic effects where there are several loci in the [[genome]] produce [[heritable]] variation in phenotype, and are thus responsible for parent-offspring resemblance<ref name=y />. The [[variance]] in additive alleles in a population (denoted V<sub>A</sub>) divided by the variance in phenotype in the population (denoted V<sub>P</sub>) produces the proportion of phenotypic variance caused by additive genetic effects, called narrow-sense [[heritability]], h<sup>2</sup><ref name=y />.
+Additive genetic effects where there are several loci in the [[genome]] produce [[heritable]] variation in phenotype, and are thus responsible for parent-offspring resemblance.<ref name=y /> The [[variance]] in additive alleles in a population (denoted V<sub>A</sub>) divided by the variance in phenotype in the population (denoted V<sub>P</sub>) produces the proportion of phenotypic variance caused by additive genetic effects, called narrow-sense [[heritability]], h<sup>2</sup>.<ref name=y />
-This [[heritable]] variation between individuals in a population or [[species]] provides a basis for [[selection]]<ref name=z>Wolf, J. B., Brodie III, E. D., Cheverud, J. M., Moore, A. J., Wade, M. J. (1998). Evolutionary consequences of indirect genetic effects. ''Trends in Ecology and Evolution'' 13(2): 64-69. doi: 10.1016/S0169-5347(97)01233-0</ref>. Narrow-sense heritability (h<sup>2</sup>) is a predictor of a trait's response to selection; increased variance in phenotype (due to strong genetic effects) causes the rate of selection to increase<ref name=y /><ref name=z />.
+This [[heritable]] variation between individuals in a population or [[species]] provides a basis for [[selection]].<ref name=z>Wolf, J. B., Brodie III, E. D., Cheverud, J. M., Moore, A. J., Wade, M. J. (1998). Evolutionary consequences of indirect genetic effects. ''Trends in Ecology and Evolution'' 13(2): 64-69. doi: 10.1016/S0169-5347(97)01233-0</ref> Narrow-sense heritability (h<sup>2</sup>) is a predictor of a trait's response to selection; increased variance in phenotype (due to strong genetic effects) causes the rate of selection to increase.<ref name=y /><ref name=z />
 ==References==