The result of a measurement on an animal is called a phenotype. Measurements should always be carried out very carefully and should be critically reviewed. Measurement errors determine how accurate phenotypes can be established.
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DefinitionA phenotype is the observed value of a trait. It is a consequence of all the enetic and environmental influences and interactions affecting the trait, including errors in measurements |
These measurement errors might have a systematic and/or random character. Systematic errors might be caused by differences between animals for example: diet composition, age at measurement, training etc. Random errors, e.g. measurements errors, may cause a low repeatability for a trait. For instance, when you want to measure the lengths of an animal, and you repeat this ten times you will see a rather large variation in outcomes. Slight movements of the animal are the cause. When you measure pelvic height, you see a rather small variation in outcomes. Two measures of accuracy of measurement are relevant: repeatability and reproducibility, both are correlations between measures on the same animal.
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DefinitionThe repeatability is defined as the extent to which measurements on the same object under similar conditions correspond with each other. It indicates how accurate a trait can be established. It is influenced only by measurement errors and time effects |
When the repeatability is low for a trait, the heritability will also be low. That means that is difficult to improve that trait in a breeding program.
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DefinitionThe reproducibility is defined here as the relationship between measurements in different locations and/or by different persons. Besides measurement errors and time effects it is also influenced by systematic effects e.g. of classifiers or technicians |
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