Unit 3, Part 7

Question 1

What is the difference between quantitative and qualitative traits?

Answer 1

Quantitative traits have many overlapping phenotypes controlled by many loci, while qualitative traits have a few distinct categories controlled by one to a few loci.

Question 2

How is variance defined in statistics?

Answer 2

Variance measures the average degree to which each point differs from the mean.

Question 3

What is the formula for calculating the mean?

Answer 3

Mean = sum of all observations / total number of samples (n).

Question 4

What does standard deviation (SD) indicate?

Answer 4

Standard deviation indicates how far apart numbers are in a data set.

Question 5

In a normal distribution, what percentage of observations fall within 1 standard deviation from the mean?

Answer 5

68% of all observations.

Question 6

What are the units of variance?

Answer 6

Units are squared (e.g., bushels², cm², lbs²).

Question 7

What is the population mean symbol?

Answer 7

The population mean is represented by μ (mu).

Question 8

What is a sample in statistics?

Answer 8

A specific group collected to make inferences about the whole population.

Question 9

True or False: The effects of alleles that affect polygenic traits follow Mendelian laws of inheritance.

Answer 9

True.

Question 10

What are quantitative traits typically affected by?

Answer 10

Quantitative traits are affected by many loci and the environment.

Question 11

Fill in the blank: Quantitative genetics is the study of quantitative traits to describe the ______ within a population.

Answer 11

variation.

Question 12

What is the symbol for sample variance?

Answer 12

Sample variance is represented by s² (s squared).

Question 13

What is the effect of each allele on polygenic traits?

Answer 13

The effects are smaller and have a cumulative effect from many loci.

Question 14

What are the three types of quantitative traits?

Answer 14

• Continuous
• Countable
• Threshold

Question 15

What does a normal distribution look like?

Answer 15

A bell-shaped curve.

Question 16

What percentage of observations in a normal distribution fall within 2 standard deviations from the mean?

Answer 16

95% of observations.

Question 17

What is the primary goal in agriculture regarding quantitative traits?

Answer 17

Shift the mean while keeping the sample distribution.

Question 18

How do you calculate standard deviation?

Answer 18

Take the square root of the variance.

Question 19

What is the symbol for sample standard deviation?

Answer 19

Sample SD is represented by s.

Question 20

What is the main challenge in predicting phenotypic results of crosses for quantitative traits?

Answer 20

More loci lead to more complex genotypes and phenotype classes.

Question 21

What is the significance of the environmental effect on genotypes?

Answer 21

It can cause the same genotype to have different phenotypes.

Question 22

What is a key component of genetic variance?

Answer 22

Each component represents different sources of genetic variation.

Question 23

What does the cumulative effect of loci contribute to in quantitative traits?

Answer 23

It results in a continuous distribution of phenotypes.

Question 24

What kind of traits are most economically important in all species?

Answer 24

Quantitative traits.

Question 25

What is the formula for calculating covariance between two variables X and Y?

Answer 25

Cov(X,Y) = average product of deviations from the means of X and Y ## Footnote Units are the products of the units of the two traits: units x units

Question 26

What does a covariance of 0 indicate?

Answer 26

No relationship between the two variables ## Footnote A covariance of 0 means that the two variables do not change together.

Question 27

What is the range of covariation?

Answer 27

-1 to +1

Question 28

What does a correlation coefficient (r) of +1 signify?

Answer 28

A perfect positive relationship

Question 29

What does a correlation coefficient (r) of -1 signify?

Answer 29

A perfect negative relationship

Question 30

True or False: Correlation implies causation.

Answer 30

False

Question 31

What is a phenotypic correlation?

Answer 31

Change in one trait is accompanied by a change in another trait

Question 32

What is a genetic correlation?

Answer 32

Selection for one trait results in a correlated response of another trait

Question 33

List examples of phenotypic correlations in animal breeding.

Answer 33

* Milk yield and percent fat * Egg weight and egg production * Back fat and growth rate * Hip score and incidence of hip dysplasia * Weaning weight and birth weight

Question 34

What does the term 'cross product' refer to in the context of covariance calculations?

Answer 34

The product of the deviations of two traits from their means

Question 35

Fill in the blank: The correlation coefficient measures the _______ of the relationship between two variables.

Answer 35

strength

Question 36

What are the three key statistical measures for birth weight in this context?

Answer 36

* Mean * Variance * SD

Question 37

What are the three key statistical measures for weaning weight in this context?

Answer 37

* Mean * Variance * SD

Question 38

What is the significance of the covariance in relation to correlation?

Answer 38

It is important for calculating the correlation between two traits

Question 39

What is the calculated covariance between birth weight and weaning weight based on the provided data?

Answer 39

0.73

Question 40

Which traits are affected by both genetics and the environment?

Answer 40

Quantitative traits

Question 41

What type of distribution is typically associated with quantitative traits?

Answer 41

Normally distributed

Question 42

True or False: Quantitative traits are discontinuous.

Answer 42

False

Question 43

What does polygenic mean in the context of quantitative traits?

Answer 43

Controlled by multiple genes