ANSC 4395 Breeding & Genetics – Test 3
(Stutts, 2025/2026 Latest Update) | Complete
Study Guide & Practice Q&A PDF
Simply-Inherited Traits - correct answertraits affected by only a few genes
qualitative or categorical
affected little by environment
Quantitative - correct answermeasured with numbers
Polygenic Traits - correct answerAffected by many genes with no gene having an
overriding influence.
- EX: Growth rate, milk production, ribeye area
Typically quantitative or continuous in expression.
- Phenotypes are usually described by numbers
Greatly influenced by environment
Examples of Simply-Inherited Traits - correct answerCoat color, horns
Examples of Polygenic Traits - correct answerWeaning weights, milk yield, REA...
CANT DO TEST MATINGS FOR THIS TYPE OF TRAIT
Threshold Traits - correct answerPolygenic traits that have categorical phenotypes
- Pregnancy, dystocia, gait
- Influenced by many genes but have an either/or result
Which traits are more important? - correct answerPolygenic traits, traits that determine
profitability and productivity
EX) Growth rate, fertility, milk production
Niche markets - correct answermarkets more sensitive to simply-inherited traits
Simply Inherited - correct answerGenetic Defects
Common characteristics of Polygenic and Simply Inherited - correct answer1. Both are
subject to the same Mendelian Mechanisms: Law of Segregation and Independent
Assortment
2. Affected by dominance and epistasis
3. Principles of selection and mating apply to both
- Attempt to increase frequency of desirable alleles
(More difficult to do with polygenic traits)
, Function of the Number of genes involved - correct answer- The more genes involved,
the more DIFFICULT it is to observe the effects of individual genes, and therefore the
less specific info we have about those genes
- When a few or one gene affects a trait, the effects of those genes are well understood
(Exact genotype may not be known, but a probable genotype may be identified.)
Test Matings - correct answerMatings designed to reveal the genotype of an individual
for a small number of loci.
- used on simply inherited traits
- Have to characterize the net effect (breeding values, expected progeny differences)
Why test matings cannot be done on polygenic traits - correct answerPolygenic traits
have so many different genes affecting them
- Cannot observe the effects of specific genes
An individual that is Aa will produce gametes - correct answer- Half will contain A, other
half will contain a
- When populations are small, there may not be exactly half of each
Three types of test matings to determine if an individual is heterozygous - correct
answer1. Mating to recessive
2. Mating to heterozygous
3. Mating sire to daughters (last resort)
Method with the highest probability of detection - correct answerMating to recessive
- Probability of siring a recessive offspring is 1/2
If the condition is deleterious - correct answer- May be hard to find homozygous
recessive
- Use known heterozygotes
- Probability of a recessive offspring is 1/4 or the probability of the offspring showing the
dominant phenotype is 3/4
If heterozygous females are hard to find, then mate sire to daughters - correct answer-
Assume the daughter's dams do not carry the recessive gene
- Probability that a daughter carries the recessive gene is 1/2 if sire is heterozygous
The probability of offspring showing the recessive phenotype is 1/8 - correct answer- 1/4
is probability of homozygous recessive from mating heterozygotes
- 1/2 comes from half of the daughters of a heterozygous male are expected to carry the
recessive gene
- Probability of dominant phenotype from this mating is 7/8
The probability of a heterozygous male having all normal offspring ______ rapidly as
the number of matings _______ - correct answerdiminishes ; increases
(Stutts, 2025/2026 Latest Update) | Complete
Study Guide & Practice Q&A PDF
Simply-Inherited Traits - correct answertraits affected by only a few genes
qualitative or categorical
affected little by environment
Quantitative - correct answermeasured with numbers
Polygenic Traits - correct answerAffected by many genes with no gene having an
overriding influence.
- EX: Growth rate, milk production, ribeye area
Typically quantitative or continuous in expression.
- Phenotypes are usually described by numbers
Greatly influenced by environment
Examples of Simply-Inherited Traits - correct answerCoat color, horns
Examples of Polygenic Traits - correct answerWeaning weights, milk yield, REA...
CANT DO TEST MATINGS FOR THIS TYPE OF TRAIT
Threshold Traits - correct answerPolygenic traits that have categorical phenotypes
- Pregnancy, dystocia, gait
- Influenced by many genes but have an either/or result
Which traits are more important? - correct answerPolygenic traits, traits that determine
profitability and productivity
EX) Growth rate, fertility, milk production
Niche markets - correct answermarkets more sensitive to simply-inherited traits
Simply Inherited - correct answerGenetic Defects
Common characteristics of Polygenic and Simply Inherited - correct answer1. Both are
subject to the same Mendelian Mechanisms: Law of Segregation and Independent
Assortment
2. Affected by dominance and epistasis
3. Principles of selection and mating apply to both
- Attempt to increase frequency of desirable alleles
(More difficult to do with polygenic traits)
, Function of the Number of genes involved - correct answer- The more genes involved,
the more DIFFICULT it is to observe the effects of individual genes, and therefore the
less specific info we have about those genes
- When a few or one gene affects a trait, the effects of those genes are well understood
(Exact genotype may not be known, but a probable genotype may be identified.)
Test Matings - correct answerMatings designed to reveal the genotype of an individual
for a small number of loci.
- used on simply inherited traits
- Have to characterize the net effect (breeding values, expected progeny differences)
Why test matings cannot be done on polygenic traits - correct answerPolygenic traits
have so many different genes affecting them
- Cannot observe the effects of specific genes
An individual that is Aa will produce gametes - correct answer- Half will contain A, other
half will contain a
- When populations are small, there may not be exactly half of each
Three types of test matings to determine if an individual is heterozygous - correct
answer1. Mating to recessive
2. Mating to heterozygous
3. Mating sire to daughters (last resort)
Method with the highest probability of detection - correct answerMating to recessive
- Probability of siring a recessive offspring is 1/2
If the condition is deleterious - correct answer- May be hard to find homozygous
recessive
- Use known heterozygotes
- Probability of a recessive offspring is 1/4 or the probability of the offspring showing the
dominant phenotype is 3/4
If heterozygous females are hard to find, then mate sire to daughters - correct answer-
Assume the daughter's dams do not carry the recessive gene
- Probability that a daughter carries the recessive gene is 1/2 if sire is heterozygous
The probability of offspring showing the recessive phenotype is 1/8 - correct answer- 1/4
is probability of homozygous recessive from mating heterozygotes
- 1/2 comes from half of the daughters of a heterozygous male are expected to carry the
recessive gene
- Probability of dominant phenotype from this mating is 7/8
The probability of a heterozygous male having all normal offspring ______ rapidly as
the number of matings _______ - correct answerdiminishes ; increases
