Quantitative Trait Loci (QTL) and Multifacforial Inheritance

Question 1

What quantitative trait loci? Give a simplified example

Answer 1

The idea is that many alleles contribute to a trait

In this simplified, and fictitious example, we will say that all genes that contribute to the trait come as 2 possible forms , and each contributes equally to attainment of stature

The dominant form (upper case) -contributes to the trait as +1

The recessive form (lower case)- does not contribute to the trait (so +0)

Question 2

How do Mendelian ratios allow you to to calculate number of possible phenotypes?

Answer 2

Phenotype= 2n(number of genotypes= n) + 1

Question 3

Why does human height come as a nuormal/Gaussian distribution?

Answer 3

This is due to there being hundreds of genes being involved, some have stronger effects, some weaker…

And importantly, environmental exposures play a role such as nutrition, exercise, parental conditions, etc.

Question 4

How can central tendency be measured?

Answer 4

• mean
• median
• mode
• half way between each extreme

Etc.

Question 5

How can we measure the distribution around mean?

Answer 5

Variation

Standard deviation

Variance

Many others

Question 6

What is variance?

Answer 6

The average of all squared distances from the mean

Question 7

What is the standard deviation?

Answer 7

The square root of the variance

Question 8

What is the range?

Answer 8

The lowest and highest values

Question 9

Give an example of experts deciding when a quantitative trait

Answer 9

When blood pressure exceeds a specific value, a cardiologist can say that the person has hypertension

Allows recommendation of lifestyle changes and treatment intervention

Question 10

Quantitative traits can be explained by…

Answer 10

Mendelian terms

Question 11

What is the phenotypic ratio of a single gene trait? Include number of phenotypic classes

Answer 11

1 gene

1-2-1

Percent individuals expressing either extreme phenotypes- 1/4

Number of phenotypic classes - 3

Question 12

Give the phenotypic ratios of a two gene trait. Include number of phenotypic classes
Include percent individuals expressing either extreme of the phenotype

Answer 12

Number of genes- 2 genes

Phenotypic ratio= 1-4-6-4-1

Percent individuals expressing either extreme of the phenotypes- 1/4^2= 1/16

Number of phenotypic classes- 5

Question 13

Give the phenotypic ratios of a 3 gene trait. Include number of phenotypic classes
Include percent individuals expressing either extreme of the phenotype

Answer 13

3 genes

Percent of individuals expressing either extreme of the phenotypes- 1/4^3= 1/64

Number of phenotypic classes= 7

Phenotypic ratio= 1-6-15-20-15-6-1

Question 14

Give the phenotypic ratios of a 4 gene trait.

Include percent individuals expressing either extreme of the phenotype

Answer 14

4 genes

Percent individuals expressing either extreme phenotype

1/4^4= 1/256

Number of phenotypic classes=9

Question 15

Give the phenotypic ratios of a 5 gene trait. Include number of phenotypic classes
Include percent individuals expressing either extreme of the phenotype

Answer 15

5 genes

Percent individuals expressing either extreme of the phenotype (1/4^5)= 1/1024

Number of phenotypic classes (2n+1)= 11

Question 16

What does the study of polygenic traits relies on statistical Analysis?

Answer 16

• normal distribution
• uses large population
• bell shape curve
• frequency histogram

Question 17

Give an example of threshold traits - all of nothing traits

Answer 17

Most babies are born without orofacial clefting

Relatively rarely, orofacial clefting is seen in a newborn

Question 18

What is threshold liability?

Answer 18

Liability is composed of contribution of genetic factors and environmental eff3ct