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Genetics > Correlation > Flashcards

Correlation Flashcards

1
Q

What is correlation?

A

measures strength of relationships between 2 variables; is one trait associated with another?

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2
Q

What are examples of correlation?

A

-Is height at withers in beef cattle associated with
body length?
-Is weight of a dairy cow related to amount of milk
produced?

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3
Q

What is correlation represented by?

A

r

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4
Q

What does r measure?

A
  • the degree of association between 2 variables (traits) in a sample from a population
  • the degree of tightness of the relationship between 2 traits
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5
Q

What range does correlation have?

A

-1.0 to +1.0 (-0.99 to +0.99)

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6
Q

What does a correlation range tell us?

A

the magnitude of the relationship (high or low) and the direction (positive or negative)

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7
Q

What does a correlation of +1.0 indicate?

A

for each standard unit increase in one variable, there is a standard unit increase in the correlated trait

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8
Q

What does a significant correlation mean?

A

that there is a high probability that there is a real association between the traits

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9
Q

What does * next to a correlation number mean?

A

number has been subject to many tests to see if it is accurate and is 95% of the time (p<0.05)

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10
Q

What does ** next to a correlation number mean?

A

99% accurate

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11
Q

Does correlation have a unit?

A

no it is unitless

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12
Q

Can correlation be used to predict the level of one variable based on another?

A

no

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13
Q

Correlation doesn’t equal_____.

A

causation

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14
Q

Why doesn’t correlation show cause and effect?

A

r provides no evidence as to which variable is the cause and which is the effect

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15
Q

Does hip height and weight have a positive or negative correlation?

A

positive

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16
Q

Does milk yield and fat % have a positive or negative correlation?

A

negative

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17
Q

Does weight and heart girth have a positive or negative correlation?

A

positive

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18
Q

Does weaning weight and yearling weight have a positive or negative correlation?

A

positve

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19
Q

Does lean cuts and backfat have a positive or negative correlation?

A

negative

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20
Q

How do you calculate the correlation coefficient?

A

know formula

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21
Q

What does a correlation coefficient of 0.01-0.2 mean?

A

low correlation

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22
Q

What does a correlation coefficient of 0.2-0.4 mean?

A

moderate/medium correlation

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23
Q

What does a correlation coefficient of >0.4 mean?

A

large correlation

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24
Q

What are the most common correlations in animal breeding?

A

phenotypic, genotypic, and environmental

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25
Q

What is phenotypic correlation?

A

measures the strength of relationship between performance (phenotypic value) in one trait and performance in another trait

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26
Q

What is genetic correlation?

A

measures the strength of relationships between breeding value for one trait and breeding value for the other

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27
Q

Why is genetic correlation important?

A

because of the concept of correlated response to selection

28
Q

What is the concept of correlated response to selection?

A

select for one trait and get response in another trait that you aren’t focusing on

29
Q

What is more important than phenotypic correlation?

A

genotypic

30
Q

What is an example of correlated response to selection?

A

as milk yield increases and is selected for, milk fat decreases because (?)

31
Q

What are the reasons for correlated response?

A

gene linkage, pleiotropy

32
Q

What is pleiotropy?

A

one gene affects more than one trait

33
Q

Is negative correlation bad?

A

NO, it just means as one increases the other decreases. It isn’t bad just as a positive correlation isn’t always good

34
Q

What is environmental correlation?

A

measure of strength of the relationship between environmental effects

35
Q

What is environmental correlation often used for?

A

management purposes

36
Q

What is rp (subscript)?

A

phenotypic correlation

37
Q

What is rg (subscript)?

A

genotypic correlation

38
Q

What is re (subscript)?

A

environmental correlation

39
Q

What is regression coefficient?

A

measures the change in Y response per unit change in X (shows one is cause and one is effect variable)

40
Q

What is the formula for regression?

A

Y=a+bx

41
Q

What does Ŷ represent?

A

predicted value of Y

42
Q

What does x represent?

A

independent (cause) variable; X observation

43
Q

What does “a” represent?

A

intercept for y axis

44
Q

What does b represent?

A

regressive coefficient (slope)

45
Q

How is regression coefficient expressed?

A

within a given range of values, positive or negative

46
Q

What can regression coefficient be used to predict?

A

one value based on another

47
Q

What does regression coefficient have?

A

representative units of traits of interest

48
Q

What is Ῡ?

A

mean of Y observations

49
Q

What does Y represent?

A

dependent (effect) variable

50
Q

What does Y represent?

A

dependent (effect) variable

51
Q

What is X (line above)?

A

mean of X observations

52
Q

What is the equation of a straight line?

A

Y=a + bx

53
Q

The greater the slope…..

A

the closer the association between 2 traits

54
Q

b=0 means?

A

no correlation

55
Q

b=0.7 means?

A

relatively close association

56
Q

When is correlation not applicable?

A

outside range of values used

57
Q

How many observations are better for correlation?

A

more

58
Q

How much degree of variation is better for correlation?

A

less

59
Q

What is regression?

A

the average of expected change in variable Y per unit change in X

60
Q

How are X and Y expressed for Regression?

A

in terms of their original units of measure

61
Q

What is byx (yx are subscript)?

A

the regression of Y on X

62
Q

What does regression assume?

A

an assumption of cause and effect

63
Q

What does variation in trait X influence?

A

variation in trait Y

64
Q

What is the cause and effect in weaning weight of cattle?

A

age is the cause of variation in weight, weight is the effect

65
Q

When is regression used?

A

when we want to predict the numerical value of one trait from the phenotypic value of another

66
Q

Is it easy to measure Y directly?

A

no it may be difficult or expensive

67
Q

Why can selecting for Y be expensive/difficult?

A

slaughtering best animals to determine qualities (yield grade or cutability of pork carcasses)

Genetics (24 decks)

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