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Description
Flashcards by Sophie Mae Neash, updated more than 1 year ago
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Created by Sophie Mae Neash
over 10 years ago
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| Question | Answer |
| Why should we reduce the number of traits we are simultaneously selecting on? | As it can have adverse effects with little genetic gain as different genes counteract eachother |
| What causes indirect selection? | In some cases it is difficult to measure the trait we want to improve on e.g. milk yield in bulls |
| How does indirect selection work? | By selecting for a second, correlated trait which can be measured |
| Why are genetic correlations important? | In animal breeding we are interested in breeding values and how they are related to one another |
| What does "genetic correlations" actually mean? | By breeding for one trait we make genetic changes in another - these can be positive or negative |
| What is the "genotype-by-environment interaction"? | When the same genotypes respond and perform differently in different environments. |
| What does it mean if traits are related in a positive manner? | They improve the efficiency of eachother |
| What does it mean if traits are related in a negative manner? | If one trait is present, the other is repressed |
| How do we measure the relationship between traits? | With a correlation coefficient |
| What are the three methods for selecting for more than one trait? | 1) Tandem selection 2) Independent culling levels 3) Index selection |
| When is tandem selection not efficient? | If the traits are negatively related to eachother |
| Describe the principles of tandem selection | After selecting for one trait for a number of generations, selection is changed to another trait |
| Why is tandem selection good? | Simple and easy method |
| Describe independent culling levels? | A culling level is set for each trait - if the animal does not reach this level then it is culled |
| What are the disadvantages of independent culling? | Do not take advantage of all the good genes in a population - if they are really good in one trait but lack in the other we get rid of the genetics for one trait |
| Describe index selection | Selecting upon an index score which combines the measure of performances of each trait weighted optimally |
| What are the advantages of index selection? | Allows animals that exceed in one trait to make a contribution to the breeding population |
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