Simply inherited traits

1. Give an example of a qualitative simply-inherited trait.

Coat color in cattle (black or red).

1. Give an example of a qualitative polygenic trait.

Conception rate (conceived or not conceived).

1. Give an example of a quantitative polygenic trait.

Weaning weight in cattle.

2A. Which trait is polygenic: conception rate or coat color?

Conception rate.

2B. What is a polygenic qualitative trait called?

A threshold trait.

3. Rank traits from easiest to hardest to improve by genetic selection.

1. Qualitative simply-inherited; 2. Quantitative polygenic; 3. Qualitative polygenic.

4. Which phenotype is recessive for cattle coat color?

Red.

4. Which phenotype is recessive for Arthrogryposis Multiplex (AM)?

Diseased.

4. Which phenotype is recessive for Tibial Hemimelia (TH)?

Diseased.

4. Which phenotype is recessive for cattle horns?

Horned.

4. Which phenotype is recessive for Porcine Stress Syndrome?

Stress susceptible.

4. Which phenotype is recessive for Rendement Napole (RN)?

Normal.

4. Which phenotype is recessive for HYPP?

Healthy.

4. Which phenotype is recessive for Overo Lethal White Syndrome?

Diseased.

4. Which phenotype is recessive for scrapie?

Susceptible (simplified; depends on PRNP genotype).

4. Which phenotype is recessive for Spider Lamb Syndrome?

Diseased.

4. Which phenotype is recessive for double muscling?

Normal in a simplified dominant model; inheritance varies.

4. Which phenotype is recessive for Developmental Duplication (DD)?

Healthy; DD is dominant with incomplete penetrance.

4. Which phenotype is recessive for Bovine Brachyspina Syndrome?

Diseased.

5. Name two ways to manage genetic abnormalities.

DNA-test and cull carriers; DNA-test and mate carriers only to noncarriers.

6. Why does crossbreeding reduce genetic abnormalities?

Most abnormalities are recessive and found in only one or a few breeds.

7. Why is selection for simply-inherited traits easier?

Only one or a few loci affect them, and the environment has little effect.

8. True or false: Some breeds do not carry certain genetic abnormalities.

True.

9. What causes recessive genetic abnormalities to appear more often?

Inbreeding increases the chance of inheriting two recessive alleles.

10A. What is Developmental Duplication (DD)?

An Angus-associated dominant abnormality with incomplete penetrance; calves may have duplicated body structures.

10A. What is incomplete penetrance?

Not every animal with the disease-causing genotype shows the abnormality.

10B. What is Overo Lethal White Syndrome?

A recessive lethal disorder in horses causing a nonfunctional colon and early death.

10B. How is OLWS related to overo coloring?

Heterozygotes may have frame-overo coloring; homozygotes develop OLWS.

10C. What is Porcine Stress Syndrome?

A recessive swine disorder causing stress sensitivity and poor meat quality.

10C. Why did breeders historically favor the PSS allele?

It was associated with increased muscling and leaner carcasses.

10C. What is Rendement Napole?

A dominant swine condition causing acidic meat and low muscle pH.

10C. Why is the RN allele dominant?

One copy causes the meat-quality phenotype.

10C. Why are splayleg and hernias not simply-inherited abnormalities?

They are complex traits affected by multiple genes and the environment.

10D. What is scrapie?

A fatal prion disease affecting the nervous system of sheep and goats.

10D. Why is codon 171 commonly tested in North America?

It is a major predictor of classical scrapie resistance or susceptibility.

10D. Why does genetic susceptibility not guarantee scrapie?

The animal must also be exposed to infectious prions.

10E. What are dairy cattle fertility haplotypes?

Inherited chromosome segments associated with recessive embryonic loss or reduced fertility.

10E. Why are they called haplotypes?

They are groups of linked genetic markers inherited together.

10E. How do fertility haplotypes relate to fertility PTAs?

Haplotypes identify specific reproductive risks; PTAs predict broader genetic merit for fertility.