Human Quantitative Traits

By: Eric PacynskiTyler Tsagalis

Human Quantitative traits are phenotypes that can vary and can be attributed to polygenic effects like the product of two genes or environment. Basically, a phenotype influenced by multiple genes.

Examples of quantitative traits include:• Morphology such as height and weight• Physiology such as blood pressure• Behavior such as aggression or depression

What is it?

Polygenic Inheritance is the inheritance of a phenotype and is attributed to two or more genes and can be measured quantitatively.

Multifactorial Inheritance is the same as polygenic inheritance but includes interactions with the environment.

Polygenic traits do not follow patterns of Mendelian traits or separated traits. Instead their phenotypes vary along a bell curve.

Polygenic and Multifactorial Inheritance

Many genetic disorders are polygenic and their phenotypes are the results of the interactions of multiple genes.

Examples of diseases that are polygenic:• Cancer• Diabetes • Epilepsy• Glaucoma• Thyroid Diseases• Alzheimer’s Disease

Polygenic Inheritance and Disease

Quantitative genetic variation, or the differences between these quantitative traits, is the substance for the evolution of the phenotypes of populations.

Quantitative genetic variation is also important for the selective breeding of certain domesticated plants and animals.

Quantitative genetic variation is used to identify a person’s vulnerability to various complex diseases and disorders.

Why are they Important?

The knowledge of the variation of quantitative traits can help us answer important evolutionary questions such as the diversity of these traits among populations and species.

This knowledge could help us increase the rate of the development of agriculturally important species like sheep or cows. It could also help us design more personalized therapeutic technologies to improve human health.

Why are they Important? (continued)

A QTL is a portion of DNA that is associated with a specific phenotypic trait and is found on different chromosomes.

Knowing the number of these QTLs can tell us about the genetic design of a trait.

It could tell us if a trait is controlled by many genes of a small effect or by a few genes of a large effect.

How to identify genes affecting quantitative traits?

Another use for these QTLs is to identify possible candidate genes that affect or are responsible for a trait.

Once a region of DNA is known to influence the phenotype of a trait, it is sequenced. The DNA sequence of any of the genes in this region is then compared to the known sequences of genes in a database whose purposes are known. This comparison is used to see which genes in this QTL affect a certain quantitative trait.

How to identify genes affecting quantitative traits? (continued)

One option to sequence the identified region of a QTL and determine the purposes of the genes is by using the online tool BLAST◦ BLAST allows users to enter a primary sequence

and look for similar sequences in a database of genes from different organisms

A simpler method for mapping a QTL is analysis of variance at the marker loci or ANOVA

Other methods include interval mapping and composite interval mapping

QTL Mapping

ANOVA disadvantages include◦ Separate estimates of QTL location and effect are not received◦ Individuals with missing genotypes must be discarded◦ Widely spaced markers result in the QTL being far from the

markers causing decreased detection Interval mapping overcomes all of the disadvantages of

the ANOVA method at the marker loci. This is the most popular approach for QTL mapping

Composite interval mapping is similar to interval mapping but it uses a subset of marker loci as covariates◦ Composite interval mapping has one major disadvantage which

is the choice of suitable marker loci to serve as covariates

QTL MappingAdvantages / Disadvantages

While the benefits of quantitative traits are many, current methods for mapping them have provided minimal results◦ Thousands of studies have been published for QTLs for

all imaginable traits and a wide range of organisms yet few actual genes belonging to QTLs have been identified

◦ Most alleles affecting quantitative traits have a very small effect on the trait, and it is clear that most experiments to map QTLs have not been large enough to find them

◦ Many QTLs that have been found often break down into multiple linked QTLs with much smaller effects when subjected to high resolution mapping

What have we learned from QTL mapping?

Yes, we can someday be able to successfully map and better understand human quantitative traits, taking all their benefits, but it will take time to find an effective way of mapping them.

Can we someday be able to successfully map large effect quantitative traits?

Images

Images

ImagesPh

enot

ype Example

graph of ANOVA QTL mapping method

What is the simplest method for mapping a QTL?A. Analysis of Variance (ANOVA)B. Interval MappingC. Composite Interval MappingD. Using the online tool BLAST

Multiple Choice Question #1

A. Analysis of Variance (ANOVA)

Answer

Which of the following is true about human quantitative traits?A. They can be influenced by multiple genesB. Human quantitative traits can help

determine a person’s susceptibility to complex diseases and behavioral disorders

C. They can be attributed to polygenic or multifactorial inheritance

D. All of the above

Multiple Choice Question #2

D. All of the above

Answer

http://jbiol.com/content/8/3/23 - Learned what human quantitative traits were in this website as well as how they are important and the results or knowledge gained from QTL mapping.

http://www.cs.cmu.edu/~epxing/Class/10810-05/Lecture9.pdf - Obtained images from this website.

http://en.wikipedia.org/wiki/Quantitative_trait_locus - Learned more in depth on what a human quantitative trait was as well as some examples of one and how it was related to diseases. Also learned what polygenic inheritance was and multifactorial inheritance, in addition to what a QTL was and the various types of QTL mapping.

Reference List