Principles of Genetics and Breeding

13.1.9.2. Within family selection

Here each family is considered a sub-population and best individual from within family are selected or culled based on their relation to their family mean.

• This method is more efficient than the above two methods. This form of selection is favoured for traits with lower heritabilities or were the trait cannot be measured on the live animal e.g. meat quality, fat content.
• Whole families are selected or rejected as units according to the mean phenotypic value of the family. This technique is of particular interest in fishes because of their high fecundity and external fertilization enables full and half sib families to be constructed.
• This technique does however require that all families be kept separate until they can be individually tagged; one of the major constraints in fish genetic studies.
• This could be a very expensive operation particularly if new facilities needed to be built.
• The limitation on the number of families means that S will be much smaller however the h² for any given trait is likely to be higher as it is based on family means so will be less influenced by environmental factors.