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Variances and covariance under positive assortative mating

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Title Variances and covariance under positive assortative mating
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Creator A.V. Rao
 
Subject positive assortative mating
one locus segregating
Two loci segregating
 
Description Not Available
The effect of positive assortative mating on genetic variance and covariance has been studied under varying conditions of dominance. The study deals separately with the situations (1) one locus segregating and (11) any number of loci segregating mating has also been dealt with giving general results for a population subject to this type of mating for ‘n’ generations. The consequences, if two loci segregating are linked have also been worked out assuming half as gene frequencies in each case. The effort of selection combined with positive assortative mating when one locus is segregating with arbitrary gene frequencies has also been investigated.
With one locus segregating and when dominance is not operating, it is found that while the positive assortative mating does not affect the mean value It increases the total genetic variance in such a way that the within family variance is halved. When dominance is operating, the mean value, however, decreases. The total genetic variance in this case, however, depends on ‘p’, the frequency of dominant allomorph and decreases or increases from generation to generation according ‘p’ is less than or greater than 0.3. The covariance between family means and parental mean values in successive generations is also affected only when ‘p’ is greater than 0.3.
With any number of loci segregating, provided the genes involved are independent in action and distribution, it has been found that the contribution of each of the genes involved to the means, variances and covariance depends only on the dominance situation characteristic of that gene, being unaffected by the dominance situation of the other genes and further that these contributions are simply additive. The contribution is also similar in form if two genes are exhibiting the same type of dominance.
In regard to the effect of linkage, when there is no dominance, it is found that linkage has no effect on the mean values, but it affects the variances and the covariance. The results in this case are parallel to those obtained by Mather (1949) under selfing, that is the definition of ‘D’ changes in the second rank variance. In the presence of dominance, however, the effect of linkage is to reduce the mean value of the previous generation to a greater extent. When the linkage is complete, between two pairs of genes, one of which shows complete dominance in the positive direction while the other shows no dominance, the two linked genes act as a single gene in expressing their additive and dominance effects, but the effect of positive assortative mating on genetic variability is not the same s found with one locus segregating, but is that as found under selfing. When both the genes show complete dominance in positive direction, and the linkage is complete, the two genes act as a single gene and the effect of positive assortative mating is now the same as found with one locus segregating.
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Date 2018-07-17T11:18:34Z
2018-07-17T11:18:34Z
1964-01-01
 
Type Dissertation/Thesis
 
Identifier A.V.Rao (1964) , Variances and covariance under positive assortative mating , Unpublished Diploma in Agricultural and Animal Husbandry Statistics, IASRI, New Delhi
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http://krishi.icar.gov.in/jspui/handle/123456789/6246
 
Language English
 
Relation Not Available;
 
Publisher ICAR-IASRI (Erstwhile IARS), New Delhi