Q genetics - Test 5

Question 1

What is the difference between a Mendelian Trait and a Quantitative Trait?

Answer 1

• Mendelian Traits are binary (+/-)
• Quantitative Traits show continuous variation

Question 2

Genes can have dominant, recessive, partial dominant (which is additive) modes of inheritance. Which do we expect contributes most to Quantitative Traits?

Answer 2

additive (partial dominant)

Question 3

How many genes contribute to 83% of withers height in horses?

Answer 3

4

Question 4

What are the two approaches typically used to study complex genetic traits?

Answer 4

GWAS and candidate gene studies

Question 5

For a QTL, if you have one genetic marker you will have the diagnostic test for the disease.

Answer 5

false: since genes for QTL’s have an additive effect, you can have one of the variants contributing to the trait but not have others. since additive no problem

Question 6

MSTN variants determine what?

Answer 6

predict the best distance… not quality of performance at distance

Question 7

Which approach was used to discover the MSTN effect on racing performance?

Answer 7

candidate gene

Question 8

The first variant associated with the MSTN effect was in an intron. Introns don’t code for amino acids in proteins, so why was this a useful maker?

Answer 8

it was in linkage disequilibrium with the variant affecting regulation

Question 9

What type of variant was later shown to influence MSTN?

Answer 9

variation in the promoter of MSTN, causing a change in rate of expression

Question 10

What was the distribution of genotypes for MSTN relative to champions at particular distances?

Answer 10

homozygotes for the ERE1 element inserted in the promoter were most common among sprinters

Question 11

What was consistent with phenotype when looking at the MSTN variants in other breeds?

Answer 11

Arabian horses had a high frequency of the variant for endurance

Question 12

Which genetic approach was used to identify the genetic variant associated with gait leading discovery of DMRT3 variant?

Answer 12

GWAS

Question 13

What is the difference between the trot and the pace?

Answer 13

pace: lateral
trot: diagonal

Question 14

What is a knockout mouse?

Answer 14

mouse with one of its genes genetically disrupted

Question 15

Why was DMRT3 chosen as the likely gate keeper gene?

Answer 15

it was the only gene in region with a stop codon; plus evidence form the knockout mouse showing effect on gait

Question 16

What is the prevalence of Gait Keeper Variant in horse breeds?

Answer 16

most common in gaited horse breeds

Question 17

What is P = G + E

Answer 17

phenotype (appearance) = genotype (genetic potential) + environment (age, nutrition, training, chance, weather, co-hort, opportunity)

Question 18

What does MSTN effect?

Answer 18

racing performance

Question 19

What does DMRT3 effect?

Answer 19

gait in horses

Question 20

Function of Myostatin (MSTN)

Answer 20

• aka growth differentiation factor (GDF8)
• inhibits muscle hypertrophy
• mutations that reduce MSTN expression result in hyperplasia and hypertrophy of muscle

Question 21

What was compared in study of MSTN?

Answer 21

sprints vs. distance races

Question 22

Candidate Gene related to MSTN

Answer 22

• variants in intron, but not likely to be significant
• high correlation for variants in introns w/ trait; can use for selection
• didn’t know cause, since no exon variants, but statistically proved gene is likely important

Question 23

What is ECA18 g.66493737C>T with MSTN?

Answer 23

• ECA18 = horse chromosome 18
• g = from reference genome sequence of Twilight
• 66493737 = this was the 66,493,373 nucleotide in reference
• C>T = mutation change from cytosine to thymadine at this position

Question 24

What can you see from TT and CC

Answer 24

• TT and CC do not predict champions
• they correlate with best distance for horse not success
• ex. a CC horse (sprinting genotype) might turn out to be a slow sprinter; but would be even worse at distance

Question 25

What does ERE1 do?

Answer 25

• effect of ERE1 insertion stronger association (2015; Santagustino et al.)
• insertion shows altered expression of MSTN (2018; Rooney et al.)

Question 26

Gait Gene Discover

Answer 26

• 65 variants and 3 genes
• one caused stop codon in DMRT3
• knockout DMRT3 in mice shows gait difference (candidate approach to validate)

Question 27

effect of Gait keeper in horses

Answer 27

• gait keeper more common among pacing Icelandic horses
• gait keeper is almost fixed in harness horses (trotters and pacers!)
• gait keeper selected in gaited breeds of horse