Sample Size and Frequency and Data Evaluation

In theory, sample size and frequency will depend on the chance of genetic contamination, the probability of genetic drift, and the importance of any genetic changes to the breeder and the scientific community.

Initially, samples of about 20 animals could be taken about three to four times per year and evaluated at the five chosen invariant and five segregating loci. Sample size and frequency could be higher if automated genotyping is available. The invariant background loci should remain reasonably invariant, though small numbers of heterozygous animals may be found, because the initial sample of animals may have missed some of the genetic variation.

Any genetic drift due to inbreeding will tend to reduce the number of heterozygous animals. Thus, data on the number of heterozygous animals summed across all five of the segregating loci can be pooled to give a single estimate of the number of heterozygous loci in 20 animals at five loci, i.e., based on 100 observations. This could be calculated for each sample and might be graphed on a Shewart control chart of the type used in industrial quality control. Such charts are available for many statistical computer programs such as MINITAB. These charts provide rules for deciding whether the process is "out of control," which in this case would suggest genetic drift or contamination. Where this occurred, it would need to be investigated in more detail.

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