Diseases - Test 5

Question 1

What does the term “genetic load” mean?

Answer 1

number of recessive disease causing genes carried by an individual

Question 2

What does the term “carrier” refer to with respect to disease genes?

Answer 2

horse w/ single copy of recessive disease gene, which is inapparent from phenotype

Question 3

Why might a partially dominant disease gene become common in a population of horses?

Answer 3

it may be linked to a desirable gene

Question 4

What’s another reason partially dominant gene may become common in population of horses?

Answer 4

it is pleiotropic, having both beneficial and deleterious effects and selected by breeders

Question 5

What is the mode of inheritance for HYPP?

Answer 5

partial dominant

Question 6

What is the mode of inheritance for SCID?

Answer 6

recessive

Question 7

HYPP appeared as a mutation in the stallion named Impressive. Why did HYPP subsequently become so common among Quarterhorses?

Answer 7

breeders selected for muscularity caused by this gene - horses w/ gene did well in halter classes

Question 8

What was the negative aspect of the HYP gene that caused some breeders to want to control it?

Answer 8

horses with this gene could experience paralysis during exercise

Question 9

The molecular basis for HYPP was discovered in 1992. What method was used to discover it?

Answer 9

candidate gene

Question 10

Was a candidate gene used to discover SCID?

Answer 10

didn’t work initially when looked at gene associated with humans but somewhat related to mouse SCID

Question 11

Which breeds of horse are affected by severe combined immunodeficiency disease?

Answer 11

Arabians

Question 12

What are the symptoms of SCID?

Answer 12

absence of immune system; death from opportunistic infections by age 3

Question 13

If you wanted information about diseases of livestock, which source would be most accurate and specific?

Answer 13

OMIA - Online Mendelian Inheritance in Animals… database created by Frank Nicholas in Australia

Question 14

Why are some genetic diseases difficult to study?

Answer 14

• breeders do not continue to breed when they occur
• some have multiple genetic causes
• some are caused by more than one gene
• some have variable symptoms (poor phenotypes)

Question 15

JEB1 and JEB2 occur in Belgian Draft horses and American Saddlebred horses, respectively. They are:

Answer 15

phenocopies

Question 16

Founders are individuals who are first known carriers of a disease gene and the source for future generations. Which of the following diseases does not have a single, known founder?

Answer 16

ACAN dwarfism: 4 different alleles, no way of knowing who had the first mutation for them, we only know there are at least 4 of them

Question 17

What is the mode of inheritance for HERDA?

Answer 17

recessive or partial dominant?

Question 18

What is the mode of inheritance for dwarfism?

Answer 18

recessive

Question 19

What is the mode of inheritance for JEB?

Answer 19

recessive

Question 20

What are problems with family studies for disease?

Answer 20

• no one collects families
• no one repeats matings that produce disease
• no one likes to find hereditary problems in blood stock

Question 21

What does HYPP mean?

Answer 21

Hyperkalemic Periodic Paralysis

Question 22

What does HYPP do?

Answer 22

• defect of sodium pump in muscle
• failure to exchange K+ and Na+
• build up of potassium
• paralysis: failure of muscle contraction response
• response varies from asymptomatic to severe
• influenced by diet: ex. alfalfa and molasses have high K+

Question 23

What does SCID mean?

Answer 23

Sever combined Immunodeficiency Disease

Question 24

What is the carrier rate for SCID?

Answer 24

in 1996, it was 8.4%

Question 25

What does MH mean?

Answer 25

malignant hyperthermia

Question 26

What kind or trait is MH?

Answer 26

dominant trait impacted by management

Question 27

What is the effect of MH?

Answer 27

usually inapparent in horses unless in surgery,
halothane anesthesia can be lethal

Question 28

How was MH found?

Answer 28

candidate gene for equine MH from human studies (RYR1)

Question 29

What does JEB mean?

Answer 29

Junctional Epidermolysis Bullosa

Question 30

What is JEB?

Answer 30

• disease of basement membrane of skin that causes sloughing of skin
• shortly after birth skin sloughs off following handling

Question 31

Where is defect found for JEB1?

Answer 31

defect of LAMC2 found in Belgian horses

Question 32

Where is defect found for JEB2?

Answer 32

defect of LAMA3 in American Saddlebred horses

Question 33

What does HERDA mean?

Answer 33

Hereditary Equine Regional Dermal Asthenia

Question 34

What is HERDA?

Answer 34

a recessive defect of skin that causes sloughing of skin under saddle; need two copies to be affected
- defect in gene PPIB

Question 35

In what horses is HERDA found?

Answer 35

Cutting horses (Quarter horses)

Question 36

What causes dwarfism?

Answer 36

• 4 variants in ACAN gene of Shetland ponies and miniature horses that are recessive causes of dwarfism + embryonic loss
• recessive SHOX defect on X/Y chromosomes of Shetland ponies and miniature horses causes recessive limb shortening
• recessive B4GALT7 defect in Friesian horses causes limb shortening

Question 37

What is the carrier rate for ACAN variants?

Answer 37

26.2%

Question 38

What is deleterious mutation load?

Answer 38

• recessive deleterious genes that exist in individuals that will cause disease
• usually very rare… spontaneous mutation but no effect on phenotype
• only appear when individual inherits two copies