Animal Breeding & Genetics Exam 2- Lecture 6: Simply Inherited Traits

Be able to depict whether a trait is simply-inherited (qualitative) or polygenic (qualitative). What are the fundamental differences between simply-inherited traits and qualitative traits at the chromosomal level, economic level, and to the extent which the environment controls its expression?

Look at how many genes are controlling the trait.

Simply-Inherited: categorical trait, cannot be measured, controlled by one or a few genes, affected little by the environment.

EX: Spider syndrome, coat color, polledness, and callipyge.

Polygenic: can be measured on a continuous scale, controlled by multiple genes at numerous loci, and heavily influenced by the environment.

EX: Economically relevant traits- milk yield, birth weight/weaning weight, marbling/tenderness, disposition, speed, and fiber grade.

If you are interested in determining the phenotype of offspring for a simply-inherited trait, what information about their parents do you need to know?

The phenotype and genotype of the animal’s parents and of the animal.

What is the purpose of constructing a test mating?Would it make more sense to construct a test mating for a trait which portrays complete dominance or a trait which portrays incomplete dominance?

1. Economic incentive to know whether the animal is homozygous or heterozygous.

2. Detection of carriers of a recessive lethal gene or genetic disorder.

3. Can only test for complete dominance.

If I wanted to setup test matings to determine if a bull is homozygous black what type of cows (genotypically) should I breed him to reduce the number of matings I need to have a high degree of confidence (>95%) that he is homo black?

A red homozygous cow, because she will pass on the recessive gene, and if the progeny turn out red the bull is heterozygous.

Discuss factors which could influence the rate at which gene frequencies can be changed through selection.

Fitness, the initial gene frequency of the population, the degree of dominance expressed at the locus with respect to fitness, and the effectiveness of selection.

Be able to determine the potential fitness between animals within a population.

Females: the greater the number of progeny they produce will increase the amount of fitness they have.

Males: males will always be more fit than females because they can have progeny with many different females. A.I is more fit than natural service.

What is the relationship between the level of fitness and the rate at which gene frequencies can be changed?

The more fit an animal is, the lower the generation interval is.