8: Statistical Characterization of a Population

Question 1

Who was the first to implement systematic selective breeding of livestock

Answer 1

1725-1795
Robert Bakewell (mostly sheep & cattle)

Question 2

Seven steps to selective breeding

Answer 2

1. Define important traits
2. Collect info available
3. Analyze the target pop
4. Present the quantitative data
5. Estimate breeding values
6. Select potential parents
7. Implement mating programs

Question 3

Main components of structured breeding programs

Answer 3

Breeding goal
Collection of performance data
Analysis of data for identification of superior animals
Use of superior animals to produce next gen

Question 4

Seven steps of a breeding program

Answer 4

1. Define production system
2. Define breeding goal
3. Collect information
4. Determine selection criteria
5. Selection and mating
6. Dissemination
7. Evaluation

Question 5

What is statistics

Answer 5

Collection and analysis of numerical data in order to investigate relationships among phenomena to explain, predict and control their occurrence

Question 6

Breeder’s job is to…

Answer 6

Improve a population of animals, not just a single animal

Question 7

How do you improve a population of animals

Answer 7

Identify a group of animals that have performance similar to the performance of the “best animal” and select them as parents for next gen

Question 8

Statistics is needed to describe and/or infer the…

Answer 8

characteristics of populations

Question 9

Population vs sample vs individuals

Answer 9

Pop = all individuals
Sample = subset of individuals taken from pop
Individual = member of the sample or of the pop

Question 10

What is a value in animal genetics? E.g.

Answer 10

Any measure applied to an individual animal as opposed to a population
e.g. phenotypic value, genotypic value, breeding value

Question 11

Animal breeders are not only concerned with individual values, but also with…

Answer 11

distributions and relationships between these values in a population

Question 12

Example of a relationship btw values in a pop

Answer 12

Do heavier cattle tend to produce heavier calves (=calving difficulty)
How does birth weight affect age at first calving

Question 13

What is a population parameter? E.g.

Answer 13

Numerical value of a pop
Often unknown, hard to measure every individual in a pop
e.g. age of first calving of all angus cows in Canada

Question 14

What is a sample statistic? E.g.

Answer 14

Any numerical measure computed from a subset of the pop
e.g. Age at first calving of 5,000 angus cows and calculate sample statistic

Question 15

What are descriptive statistics

Answer 15

A summary statistic that quantitatively describes or summarizes features of data

Question 16

What are inferential statistics

Answer 16

Statistical tests to determine genetic and env effects, variation and facilitate breeding decisions

Question 17

What is a qualitative (monogenic) trait

Answer 17

Phenotypes that fall into distinct classes or categories
e.g. polled vs horned

Question 18

Three types of quantitative (polygenic) traits

Answer 18

1. Continuous
2. Meristic
3. Threshold

Question 19

What are continuous polygenic traits? E.g.

Answer 19

Have a scale of measurement that is naturally continuous e.g. milk production in kg

Question 20

What are meristic quantitative traits? E.g.

Answer 20

Counting quantitative features, exhibit a large number of discrete classes (e.g. # of piglets born alive)

Question 21

What are threshold quantitative traits? E.g.

Answer 21

Continuously distributed phenotypes with some trait value that defines an upper or lower limit (threshold)
e.g. healthy vs diseased animal

Question 22

Slide 20

Answer 22

E.g. of threshold trait graph

Question 23

The infinitesimal model assumes that…

Answer 23

all traits are determined by a high number of genes, each with an infinitely small effect, and environmental effects

Question 24

Animal breeding wants to predict… What helps us with that

Answer 24

Predict genetic potential of animals and how the next generation will improve if we use a certain proportion of animals as parents
Normal distribution (comes with set of statistical rules)

Question 25

What are measures of central tendency/location

Answer 25

Mean, median and mode

Question 26

What are measures of variability/ dispersion

Answer 26

Standard deviation, variance, minimum and maximum variables

Question 27

What is the mean

Answer 27

Sum of all measurements divided by the number of measurements

Question 28

What is variance

Answer 28

Average squared deviation of the observations from the mean

Question 29

N vs n

Answer 29

N = pop
n = sample

Question 30

Slide 24

Answer 30

Mean/variance equations

Question 31

What is median? Mode?

When is mean=mode=median

Answer 31

Median = value in the middle of the data set
Mode = value that occurs most often

Under normal distribution

Question 32

What is standard deviation

Answer 32

Square root of the variance, thus has the same measure unit as the mean

Question 33

Slide 28

Answer 33

*** memorize top curve
Divide by two bc its only half of the data points btw 95 and 68%

Question 34

Mean calving interval in beef cattle? With a standard deviation of…

Answer 34

380 days +/- 20 days

Question 35

Mean milk yield in dairy cows? With a standard deviation of…

Answer 35

13,000lbs +/- 560lbs