Author
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Van Vleck, Lloyd |
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Submitted to: Brazilian Journal of Genetics
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/30/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Analyses of records of crossbred animals or of records of animals of composite breeds require calculation of the fractional genetic contribution of each breed to all animals with records and also to all dams of those animals if maternal effects are important. In most cases animal and maternal heterosis must also be included in the model for analysis. Thus, heterozygosity fractions which correspond to interactions between breed effects must also be calculated. For simple designs such calculations are easy to do. After a few generations of matings or with many breeds involved the calculations become much more complicated. This paper describes simple steps to calculate fractional breed contributions to each animal and its dam and also calculation of animal and maternal heterozy- gosity fractions. The first steps involve basic recoding of identifi- cation numbers which can be accomplished easily using the MTDFNRM program which is a part of the MTDFREML package used to estimate genetic parameters. The paper then outlines the computational steps to calculate breed and heterozygosity fractions using the recoded pedigree file from the MTDFNRM program. The last step describes how to insert these fractions into a data file. The fractions can then be used as regression variables for estimation of breed direct and maternal genetic effects and also effects and also effects of direct and maternal heterosis. Technical Abstract: Teaching, research, and herd breeding applications may require calculation of breed additive contributions for direct and maternal genetic effects and fractions of heterozygosity associated with breed specific direct and maternal heterosis effects. These coefficients can be obtained from the first NB rows of a pseudo numerator relationship matrix where the first NB rows represent fractional contributions by breed to each animal or group representing a specific breed cross. The table begins with an NB x NB identity matrix representing pure breeds. Initial animals or represen- tative crosses must be purebreds or two breed crosses. Parents of initial purebreds are represented by the corresponding column and initial two-breed cross progeny by the two corresponding columns of the identity matrix. After that, usual rules are used to calculate the NB column entries corresponding to breeds for each animal. The NB entries are fractions of genes expected to be contributed by each of the pure breeds and correspond to the breed additive direct fractions. Entries in the column correspond- ing to the dam represent breed additive maternal fractions. Breed specific direct heterozygosity coefficients are entries of an NB x NB matrix formed by the outer product of the two NB by 1 columns associated with sire and dam of the animal. One minus sum of the diagonals represents total direct heterozygosity. Similarly, the NB x NB matrix formed by the outer product of columns associated with sire of dam and dam of dam contains breed specific maternal heterozygosity coefficients. These steps can be programmed to create covariates to merge with data. |
