Stutts ANSC 4395 Breeding & Genetics
Exam Test 3 With 100% Correct And
Verified Answers
Simply-Inherited Traits - Correct Answer-traits affected by only a
few genes
qualitative or categorical
affected little by environment
Quantitative - Correct Answer-measured with numbers
Polygenic Traits - Correct Answer-Affected 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 Answer-Coat color,
horns
Examples of Polygenic Traits - Correct Answer-Weaning weights,
milk yield, REA... CANT DO TEST MATINGS FOR THIS TYPE
OF TRAIT
Threshold Traits - Correct Answer-Polygenic traits that have
categorical phenotypes
- Pregnancy, dystocia, gait
- Influenced by many genes but have an either/or result
Which traits are more important? - Correct Answer-Polygenic
traits, traits that determine profitability and productivity
EX) Growth rate, fertility, milk production
, Niche markets - Correct Answer-markets more sensitive to simply-
inherited traits
Simply Inherited - Correct Answer-Genetic Defects
Common characteristics of Polygenic and Simply Inherited -
Correct Answer-1. 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 Answer-Matings 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
Answer-Polygenic 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
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