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AN SC 384 > 22: Genetic Change > Flashcards

22: Genetic Change Flashcards

1
Q

What is genetic change

A

Change due to selection
Rate of change in the mean BV from one generation to another in a pop due to selection

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2
Q

Rate of genetic change aka

A

Response to selection

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3
Q

Four factors affecting the rate of genetic change

A
  1. Accuracy of selection
  2. Selection intensity
  3. Genetic variation
  4. Generation interval
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4
Q

What is accuracy of selection

A

Accuracy of BV prediction
Strength of the relationship between true BVs and their predictions (EBV) for a trait under selection

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5
Q

Accuracy of selection is the correlation between…

A

TBV and EBV (r BV, BV^)

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6
Q

EBV provides an estimate of…

A

the genetic potential of each animal

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7
Q

What is a major factor affecting accuracy of selection?

A

Heritability (h^2)
Strength of the relationship between performance and BVs

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8
Q

How to increase heritability

A

Managing animals uniformly, adjusting for environmental effects
Using more information (pedigree and own performance)

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9
Q

Range of accuracy

A

0 (not informative) to 1 (very accurate)

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10
Q

The lower the accuracy of an EBV, the higher the risk of…

A

ranking the animals in the wrong order and the larger the risk of a change in EBV when new information sources (e.g. offspring) become available

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11
Q

What is selection intensity (i)

A

How “choosy” breeders are in deciding which individuals are selected to be parents of the next generation
Animals selected based on selection criteria e.g. phenotypic values, BVs

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12
Q

What is high intensity vs no intensity selection

A

High = choosing only the very best individuals based on
selection criteria

No = choosing animals purely at random

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13
Q

Equation for selection intensity

A

mean selection criteria for individuals selected as parents minus average selection criteria of all potential parents

divided by standard deviation of the selection criteria

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14
Q

What is selection differential

A

Numerator of selection intensity equation

size of the difference in performance between the parents and the total population

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15
Q

What is selection intensity with truncate selection

A

Selection on the basis of a distinct division in the selection criterion (point of truncation) above which individuals are kept and below which they are rejected

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16
Q

What is proportion saved (p)

A

Number of individuals chosen to be parents of the next generation in selection intensity w truncate selection

17
Q

Why can’t proportion of saved animals be unlimitedly small?

A
  1. Selected animals need to be able to produce sufficient number of offspring to replace the entire generation of animals
  2. Large inbreeding rate
18
Q

What is genetic variation

A

Variability of BVs within a population for a trait under selection

19
Q

Difference in genetic change for high vs low genetic variation

A

High/large: rate of genetic change will be fast

Low/little: rate of genetic change will be slow

20
Q

What is low genetic variation

A

Small range of BV and the best individuals are only slightly better than the worse/above average, so will their progeny, rate of change is slow

21
Q

What is high genetic variation

A

High range of BV and the best animals are far superior to the worst
Selected individuals and their offspring will be far better than average, rate of change is fast

22
Q

What is generation interval (L)

A

Amount of time required to replace one generation with the next
Average age of the parents at birth of their offspring

23
Q

Shorter the generation interval, the…

A

faster the rat of genetic change

24
Q

What is realized response to selection (R)

A

difference in average performance or average breeding value between two generation

25
Q

Selection differential vs selection response

A

Differential = superiority of the selected parents in comparison to their generation

Response = superiority of the offspring in comparison to their parents

26
Q

What is a genetic trend

A

Change in mean breeding value of a population over time

27
Q

Existence of genetic trends suggests…

A

Accuracy of selection, selection intensity, genetic variation and generation interval are not constant; change over time

28
Q

Trade-offs between selection intensity and generation interval

A

Increase in selection intensity is associated with an increase in generation interval and vice versa

29
Q

Trade-off between accuracy and generation interval

A

Decrease in generation interval usually causes a decrease in accuracy of selection (fewer records available for genetic prediction)

30
Q

Trade-offs between accuracy and selection intensity

A

Increase in accuracy of selection is often accompanied by a decrease in selection intensity and vice versa (fewer bulls, more records on each bull = greater accuracy but lower selection intensity)

AN SC 384 (22 decks)

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