8: Statistical Characterization of a Population Flashcards
Who was the first to implement systematic selective breeding of livestock
1725-1795
Robert Bakewell (mostly sheep & cattle)
Seven steps to selective breeding
- Define important traits
- Collect info available
- Analyze the target pop
- Present the quantitative data
- Estimate breeding values
- Select potential parents
- Implement mating programs
Main components of structured breeding programs
Breeding goal
Collection of performance data
Analysis of data for identification of superior animals
Use of superior animals to produce next gen
Seven steps of a breeding program
- Define production system
- Define breeding goal
- Collect information
- Determine selection criteria
- Selection and mating
- Dissemination
- Evaluation
What is statistics
Collection and analysis of numerical data in order to investigate relationships among phenomena to explain, predict and control their occurrence
Breeder’s job is to…
Improve a population of animals, not just a single animal
How do you improve a population of animals
Identify a group of animals that have performance similar to the performance of the “best animal” and select them as parents for next gen
Statistics is needed to describe and/or infer the…
characteristics of populations
Population vs sample vs individuals
Pop = all individuals
Sample = subset of individuals taken from pop
Individual = member of the sample or of the pop
What is a value in animal genetics? E.g.
Any measure applied to an individual animal as opposed to a population
e.g. phenotypic value, genotypic value, breeding value
Animal breeders are not only concerned with individual values, but also with…
distributions and relationships between these values in a population
Example of a relationship btw values in a pop
Do heavier cattle tend to produce heavier calves (=calving difficulty)
How does birth weight affect age at first calving
What is a population parameter? E.g.
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
What is a sample statistic? E.g.
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
What are descriptive statistics
A summary statistic that quantitatively describes or summarizes features of data
What are inferential statistics
Statistical tests to determine genetic and env effects, variation and facilitate breeding decisions
What is a qualitative (monogenic) trait
Phenotypes that fall into distinct classes or categories
e.g. polled vs horned
Three types of quantitative (polygenic) traits
- Continuous
- Meristic
- Threshold
What are continuous polygenic traits? E.g.
Have a scale of measurement that is naturally continuous e.g. milk production in kg
What are meristic quantitative traits? E.g.
Counting quantitative features, exhibit a large number of discrete classes (e.g. # of piglets born alive)
What are threshold quantitative traits? E.g.
Continuously distributed phenotypes with some trait value that defines an upper or lower limit (threshold)
e.g. healthy vs diseased animal
Slide 20
E.g. of threshold trait graph
The infinitesimal model assumes that…
all traits are determined by a high number of genes, each with an infinitely small effect, and environmental effects
Animal breeding wants to predict… What helps us with that
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)
What are measures of central tendency/location
Mean, median and mode
What are measures of variability/ dispersion
Standard deviation, variance, minimum and maximum variables
What is the mean
Sum of all measurements divided by the number of measurements
What is variance
Average squared deviation of the observations from the mean
N vs n
N = pop
n = sample
Slide 24
Mean/variance equations
What is median? Mode?
When is mean=mode=median
Median = value in the middle of the data set
Mode = value that occurs most often
Under normal distribution
What is standard deviation
Square root of the variance, thus has the same measure unit as the mean
Slide 28
*** memorize top curve
Divide by two bc its only half of the data points btw 95 and 68%
Mean calving interval in beef cattle? With a standard deviation of…
380 days +/- 20 days
Mean milk yield in dairy cows? With a standard deviation of…
13,000lbs +/- 560lbs
