Genetic Basis

Question 1

Heritability

Answer 1

The percentage by which a gene can be passed from a parent to their offspring; the higher the heritability, the easier it is to breed for that trait
Ex. Slower gaits are less heritable, while faster gaits are more heritable

Question 2

Performance Measures

Answer 2

Measure traits across populations of horses

Ex. speed, heart rate, etc.

Question 3

Myostatin, “Speed Gene”

Answer 3

Controls muscle growth and development, including stopping excessive muscle growth
Follistatin (hormone) at receptor proteins inhibits myostatin
Mutation to myostatin allows for excessive muscle production (muscle hypertrophy) in several forms:
C:C (fast twitch), C:T (middle twitch), T:T (slow twitch)
TB’s have been selectively bred for the myostatin mutation, and it is now generally “fixed” in the population; first sire - Bold Ruler
QH’s also select for the mutation, especially fast twitch for speed events, and extra muscling for halter; first sire - Impressive

Question 4

Genetic Assessments

Answer 4

Simple assessments, done with weight tapes, etc.
Blood and DNA analysis
Test for gait variability (highly heritable traits) using sensors to measure movement
GWAS (Genetic Wide Association Studies) - ID’s satellite markers for known genes of interest
Microarrays - dated; measure expression of large numbers of genes
Whole Genome Sequencing - from lymphocyte sample; lots of information, much of it useless

Question 5

Genetics

Answer 5

Horses have 20,000 genes, 18,000 are expressed, and fewer are fully expressed as proteins

Question 6

Five-Panel Test for QH’s

Answer 6

To be eligible to breed under AQHA, must be negative for the following five genetic diseases:

1. Malignant Hyperthermia (MH) - Ca storage issue, builds up in cytoplasm and causes heat buildup, twitching, stiffness
2. Glycogen Branching Enzyme Deficiency - not prevalent, prevents the storage of glycogen, fatal
3. Hyperkalemic Periodic Paralysis (HYPP) - elevated potassium concentrations in blood, causes paralysis, falling over, can effect heart rate
4. Polysaccharide Storage Myopathy (PSSM) - excessive glycogen storage in muscle, where it cannot be used
5. Hereditary Equine Reginal Dermal Asthenia (HERDA) - weakend extracellular matrix between dermal and muscle layer, causing skin to weaken and fall off