Download Human Quantitative Traits

By: Eric Pacynski
Tyler Tsagalis
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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
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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.
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Many genetic disorders are polygenic and
their phenotypes are the results of the
interactions of multiple genes.
Examples of diseases that are polygenic:
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Cancer
Diabetes
Epilepsy
Glaucoma
Thyroid Diseases
Alzheimer’s Disease
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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.
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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.
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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.
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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.
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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
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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
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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
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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
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.
Phenotype
Example
graph of
ANOVA
QTL
mapping
method
What is the simplest method for mapping a
QTL?
A. Analysis of Variance (ANOVA)
B. Interval Mapping
C. Composite Interval Mapping
D. Using the online tool BLAST
A. Analysis of Variance (ANOVA)
Which of the following is true about human
quantitative traits?
A. They can be influenced by multiple genes
B. 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
D. All of the above
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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/1081005/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.