Animal Breeding & Genetics Exam 2- Lecture 9: The Rate of Genetic Change

What are the four factors which impact the rate of genetic change? (Be able to explain each in your own words)  As each of these four factors is increased is the rate of genetic change increased or decreased?

1. Accuracy of Selection (Rate of Genetic Change increases, when this is increased.)

2. Selection Intensity (Rate of Genetic Change increases, when this is increased.)

3. Genetic Variation (Rate of Genetic Change increases, when this is increased.)

4. Generation Interval (Rate of Genetic Change decreases, when this is increased.)

What impact does the heritability of the trait under selection have on the accuracy of selection? 

When heritability is increased the accuracy of selection is increased.

Compare the accuracy of selection between the following selection practices: random selection, subjective live evaluation, actual performance records, parentage performance records, marker assisted technology, and EPDs?

 

Random selection —> Subjective live evaluation —>Actual performance records —> Parentage performance records —> Marker assisted technology —> EPDs

Explain what a High Density Marker Panel is and how this information is incorporated into a GE-EPD. Would this technology be more relevant for younger animals or older proven parent animals?

A DNA marker test that identifies the presence of 50,000 loci associated with quality grade, marbling, and 14-20 other traits. It is better on younger animals because it is more accurate.

Memorize the formula for selection differential and selection intensity.  Be able to work example problems.  In what units are each of these measured?

S= SCs-SC

S= Selection differential (expressed in units of the selection criterion)

SCs= The mean selection criterion of those individuals selected to be parents

SC= The overall mean selection criterion of all potential parents

i= SCs-SC/osc

i= selection intensity

osc= the standard deviation of the selection criterion when the given population

Assume I have a pool of 100 heifers in which to choose replacements from.  Would selection intensity be greater if I kept back 50 of them or 20?  Why?

Selection intensity would be greater if 20 were kept vs. 50, because by keeping fewer more genetically superior heifers, you are being more picky about what you are selecting.

Is there more genetic variation present in an inbred program or an outbred program?  Although there is differences in genetic variation between these two types of mating strategies understand that the amount of genetic variation inherent in a population has the least to do with the rate of genetic progress compared to accuracy of selection, selection intensity, and generation interval.

Outbred, because the more outliers you have the better chances there are to make genetic progress.

In a closed population, how would you determine what the generation interval is?

GI is equal to the mean age of the female base when their offspring are born.

Is accuracy of selection, selection intensity, genetic variation, and generation interval fixed or are they always changing within a population?

They are always changing within a population, creating new genetic trends.

Do individual dams or sires have more of an impact on the genetic base of a herd?  Hypothetically, what should the impact of sires vs. dams be on selection intensity and accuracy of selection?

Sires, fewer males are needed than females, you can’t be picky with females, whereas with males you can be very selective.