Additional Learning Objectives for the Breeding and Genetics Module

Breeding Objectives. Determining What Animal is “Best” for Your Production System and Climate.

Points to understand

Factors which can cause distortion in breeding objectives.
The difference between traits and phenotypes.
How knowledge of interactions involving genotype helps us determine breeding objectives.
How correctly defining end users and understanding the end user’s system leads you to more appropriate breeding objectives.

Skills to Acquire

Describe the system that is your farm or ranch by listing specific components of the system and categorizing them appropriately.
Describe whom are the end users of your genetics or animal product, and justify your production system.

How Are Animal Populations Improved?

Points to understand

The difference between selection and mating.
How selecting parents with better breeding values improves future generations.
How heritability influences the effectiveness of selection.
How information on relatives increases the effectiveness of selection.
The difference between simply-inherited and polygenic traits, and how selection differs for each.
The difference between complementarity and hybrid vigor.
How selection and mating can be interdependent.

Skills to Acquire

List commonly measured traits that comprise performance testing programs in meat goats.

The Basics in the Biology of Genetics – Mendelian Inheritance; It Ain’t All Dominance & Recessive

Points to understand

How to distinguish among genes, alleles, and loci.
Mendel’s laws of segregation and independent assortment and their significance in determining breeding values.
How linkage, crossing over, and recombination affect assortment of genes that are a part of the same chromosome.
Various forms of dominance, and epistatis.

Skills to acquire

Use Punnett squares to predict the possible outcomes of matings.
Calculate the number of unique gametes a specified genotype can produce and the number of unique zygotes possible from the mating of two specified genotypes.
Use a schematic diagram to illustrate the different forms of dominance.

Genes in a Population

Points to understand

Understand the difference between gene and genotypic frequencies.
Be able to explain how selection affects gene and genotypic frequencies.

Skills to acquire

Calculate gene and genotypic frequencies in a population.
Combine Punnett squares and gene frequencies to determine genotypic frequencies of offspring.

Simply-Inherited and Polygenic Traits

Points to understand

The difference between simply-inherited and polygenic traits.
The difference between quantitative (continuous) and qualitative (categorical) traits.
The common characteristics of simply-inherited and polygenic traits.

Skills to acquire

Define threshold traits in terms of simply-inherited/polygenic and quantitative/qualitative categories.
Classify many commonly measured traits by simply-inherited/polygenic and quantitative/qualitative categories.

The Genetic Model for Quantitative Traits

Points to understand

What a genetic model represents: the general factors affecting a single performance record.
The relationship between progeny difference and breeding value.
Why gene combination effects are not additive, nor transmittable from parent to offspring.

Skills to acquire

Construct column charts to represent hypothetical examples of the various genetic models.
Predict breeding value and performance of offspring from the breeding values of their parents.

Simple Statistics and Their Application to Quantitative Traits

Points to understand

The difference between individual values and population measures.
What the area under a segment of the curve of a normal distribution represents.
Why polygenic, quantitative traits are typically normally distributed.
Mean and variation.
The importance of variation and uniformity in animal breeding.
How most components of the genetic model has variation associated with it.
The differences between the two measures of variation: variance and standard deviation.
Covariation and its importance in animal breeding.
Difference between positive, negative, and zero covariation.
Three aspects of covariation and the differences among its three measures: covariance, correlation, and regression.
The purpose of regression values.
The elements of a simple prediction equation and how the equation works.

Skills to acquire

Draw a normal distribution, label both axes, and indicate the mean and the distance represented by a standard deviation.
Calculate a sample mean, variance, and standard deviation from a set of data.
Calculate a covariance, correlation coefficient, and regression coefficient from a set of data.
Calculate correlation and regression coefficients given appropriate variances and covariances.
Label the components of a simple prediction equation and use it in an example.

The Concepts of Heritability and Repeatability

Points to understand

The definition of heritability.
Why the fact that a trait is genetically determined does not necessarily make it heritable.
The relationship between heritability and accuracy of selection.
The importance of heritability to genetic prediction.
How knowledge of heritability can help a producer make management decisions.
Define repeatability.
How repeatability can be used to help make culling decisions.
How environmental uniformity, accurate measurement, mathematically adjusting for known environmental effects, and contemporary groups can be used to improve heritability and repeatability.
How the use of deviations from contemporary group means or how using trait ratios decreases environmental variation.

Skills to acquire

Calculate heritability given appropriate variances, covariances, and(or) regressions.
Construct column charts and scatter plots illustrating high and low repeatability.

Factors Affecting the Rate of Genetic Change

Points to understand

Five elements of the key equation for genetic change: rate of genetic change, accuracy of selection, selection intensity, genetic variation, and generation interval.
How it is possible to simultaneously have low accuracy and high intensity and vice versa.
How “proportion saved” is related to selection intensity under truncation selection.
Why selection intensity is often poor with phenotypic selection for a threshold trait, and why improvement in the trait leads to even worse selection intensity.
Why the elements of the key equation change over time.
The trade-offs among elements of the key equation: accuracy versus generation interval; accuracy versus intensity; intensity versus generation interval in each sex.
Why male selection is so much more important than female selection, and why there are limitations to the rate of genetic change when sires are purchased.

Skills to acquire

Use a particular formula of your choice to predict the rate of genetic change in a population.
Make practical decisions about the design of a breeding program using the key equation for genetic change or its variants.

Genetic Prediction

Points to understand

Why genetic prediction technologies are important.
The several kinds of data commonly used in genetic prediction.
The factors affecting accuracy of prediction.
The relative importance of individual performance information versus relatives’ information at different levels of heritability.
Why pedigree information is important but often of limited value.
Why progeny information is especially valuable.
Why additional records are more informative when data are “scarce” than when data are abundant.
The difference between direct, maternal, and paternal components of traits.
The meaning of total maternal value.

Skills to acquire

Calculate single-source predictions of breeding values, progeny differences, and producing abilities, when given appropriate formulas for regression coefficients and associated accuracies.
Convert an accuracy value to a 68% confidence range.
Given direct and maternal EBVs or EPDs and predictions of permanent environmental effects, calculate total maternal value and MPPA.

Genetic Evaluation

Key points to understand

The rationale for genetic evaluation and methods for treating data.
The merits of designed central tests versus analyses of field data.
The differences among the various kinds of EPDs expected to exist for meat goats.
Understanding that genetic predictions are tools for comparing animals.
What a genetic prediction of zero from a genetic evaluation really means.
How measures of accuracy can be used to determine both selection risk and the likelihood that differences in genetic predictions between animals are meaningful.
That accuracy measures reveal nothing about uniformity of progeny.
The kinds of problems that cause errors in genetic evaluation.

Correlated Responses to Selection

Points to understand

The chief cause of correlated response to selection.
That the (mathematical) sign of a correlation does not indicate whether the correlation is favorable or unfavorable
The factors affecting correlated response to selection.
The conditions that favor indirect selection for an indicator trait over direct selection.
How some genetic correlations can be helpful and others detrimental.

Skills to acquire

Calculate correlation from appropriate variances and covariances.
Given some required parameters, calculate response to selection.

Multiple-Trait Selection

Key points to understand

Aggregate breeding value or net merit.
The differences among and relative merits of the three methods of multiple-trait selection: tandem selection, use of independent culling levels, and use of economic selection indexes.
The structure of a breeding objective.
The criteria for determining traits in a breeding objective and traits in a corresponding index.
Why selection intensity for and genetic change in individual traits is lower under multiple-trait selection than under single-trait selection for those traits.
General guidelines for determining whether a trait merits efforts in selection.

Skills to acquire

Use independent culling levels to choose a set of replacements given performance data or genetic predictions.
Use an economic selection index to choose a set of replacements given performance data or genetic predictions.

Mating Systems for Simply-Inherited Traits

Key points to understand

What information is needed to make mating decisions for simply-inherited traits.
How to use repeated backcrossing or introgression to import an allele from another population.
How repeated backcrossing to import an allele differs from grading up.

Skills to acquire

Determine probabilities of parent genotypes from pedigree information and estimates of gene frequencies.
Calculate probable proportions of offspring genotypes given probabilities of parent genotypes.

Mating Strategies Based on Pedigree Relationship: Assortative mating, Inbreeding, and Outbreeding

Points to understand

How random, positive assortative, and negative assortative mating differ and for what purposes each should be used.
The concept of complementarity.
The value of crossing maternal and paternal breeds or lines.
The effects of inbreeding on homozygosity, prepotency, expression of deleterious recessive genes, and inbreeding depression.
The mechanism by which inbreeding causes inbreeding depression, and outbreeding causes hybrid vigor or heterosis.
How inbreeding and relationship coefficients are defined.
How linebreeding differs from inbreeding.
The effects of inbreeding on uniformity in simply-inherited and polygenic traits.
Why crosses of less related breeds and lines produce more hybrid vigor than crosses of more closely related breeds or lines.
The major purposes of outbreeding: hybrid vigor and complementarity.
Why inbreeding is practiced mostly by seedstock producers and outbreeding is practiced mostly by commercial producers.

Skills to acquire

Use the genetic model for quantitative traits to explain why animals usually show little hybrid vigor for highly heritable traits and more hybrid vigor for lowly heritable traits.
Calculate inbreeding and relationship coefficients using the path and tabular methods.

Hybrid Vigor or Heterosis

Key points to understand

That hybrid vigor generated by crossing breeds or lines is simply a restoration of hybrid vigor lost in inbreeding.
That superior crosses provide consistently more hybrid vigor and better performance than is possible with the original base population.
How hybrid vigor or heterosis is measured.
The trade-off between maximizing hybrid vigor and maintaining breeding value and performance.
The differences among individual, maternal, and paternal hybrid vigor.
Why hybrid vigor declines from the F1 to the F2 generation and then remains constant in more advanced generations of hybrids.
How recombination loss can cause further decline in hybrid vigor beyond the F2 generation.
Why hybrid vigor declines in each backcross generation.

Skills to acquire

Calculate hybrid vigor and percent hybrid vigor from performance data for purebred parent populations and F1 crosses.
Design a breeding program that takes advantage of individual, maternal, and paternal hybrid vigor.
Calculate estimates of hybrid vigor.
Predict phenotypic performance of crosses involving any combination of breeds.

Crossbreeding Systems

Key Points to Understand

Why crossbreeding systems, based on good purebred stock, are needed in commercial production.
How rotational crossbreeding systems work.
How static terminal systems and rotational/terminal systems work.
How a composite animal differs from a hybrid.
Why composites can play both commercial and seedstock roles.
How inbreeding can be avoided in developing composite populations.
Strategies for increasing uniformity within a herd or flock.
Why it is so difficult to decrease genetic variation in polygenic traits.

Skills to Acquire

List five criteria used to evaluate crossbreeding systems and explain the rationale for each.
Calculate the percentage of F1 hybrid vigor retained in rotational systems using either purebred or crossbred sires.
Calculate the percentage of F1 hybrid vigor retained in advanced generations of various composite breeds.

Biotechnology and Animal Breeding

Key points to understand

Two general categories of biotechnologies.
Factors determining the impact of a biotechnology.
The advantages and disadvantages of the following reproductive technologies: artificial insemination, embryo transfer, in vitro fertilization, sex control, production of clones from embryonic tissue, production of clones from adult tissue, and same-sex mating.
Why multiple cycles of cloning are required for continuous genetic change.
The need for preservation of animal germ plasm.
How reproductive technologies can be used to preserve germ plasm.
The advantages and disadvantages of the following molecular technologies: DNA fingerprinting, marker assisted selection for simply-inherited traits, marker assisted selection for polygenic traits, and gene transfer.
Why genetic markers must be closely linked to genes of interest.
The usefulness of detailed gene maps.
Why marker assisted selection may be more valuable for simply-inherited traits than for polygenic traits.
Why marker assisted selection for polygenic traits may be more valuable for traits that have been subject to little selection pressure in the past.
How information on genetic markers can be incorporated in genetic evaluation programs.

Summary Issues in Breeding Meat Goats

Key points to understand

The attributes that successful meat goat breeders tend to have in common.
How these attributes contribute to the success of breeding programs.

Ethics in Meat Goat Breeding and Merchandizing

Key points to appreciate

Longterm business success depends on treating people right and being honest in husbandry practices.
Breeding for functional animals without major defects.
Commercial meat goat needs should drive the selection program of purebred breeders.
Get those registration papers transferred on time.

In developing this module I have been guided by and have included selected examples from the textbook I have used for several years in teaching the Animal Breeding and Small Ruminant Management courses at Fort Valley State University. That book, entitled “Understanding Animal Breeding,” was written by Dr. Rick Bourden at Colorado State University. It is a recommended reference for goat breeders who have a serious interest be becoming a student of the discipline. Examples specific to goats in general and to meat goats in particular are cited when discussed.

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