Transcript Quantitative Genetics - Mediapolis Community School

Quantitative Genetics
Chapter 25
Overview
Complex traits = characteristics that are
determined by several genes and are
significantly influenced by environmental
factors.
Quantitative traits = traits that can be described
numerically.
Quantitative genetics = the field of genetics that
studies the mode of inheritance of complex or
quantitative traits.
Quantitative Traits
• Humans all have the same basic anatomical
features (two eyes, two ears, etc.) but differ in
quantitative ways.
– People vary in height, weight, the shape of facial
features, pigmentation, and many other
characteristics.
Quantitative Traits, cont.
Quantitative traits can be broken down into 4
main categories:
1.
2.
3.
4.
Anatomical
Physiological
Behavioral
Diseases
Measurement of Quantitative Traits
• The measurement of quantitative traits is
essential when comparing individuals or
evaluating groups of individuals.
– For example: it is not very informative to say that
two people are tall, but if we say that one person
is 6 feet 4 inches and the other is 6 feet 7 inches.
***quantitative measurement is how we describe
phenotype.
Biometrics
• Created in the early 1900’s by Francis Galton
and his student Karl Pearson (no relation) in
England.
• = the statistical study of biological traits.
Example
• Ears of corn have the following lengths: 15,
14, 13, 14, 15, 16, 16, 17, 15, and 15.
• In genetics we are often interested in the
amount of phenotypic variation that exists in a
group.
• A common way to evaluate variation within a
population is with a statistic called the
variance, which is the measure of the
variation from the mean.
Variance
= the sum of the squared deviations from the mean
divided by degrees of freedom.
Corn example:
= 4(15-15)2 + 2(14-15)2 + (13-15)2 + 2(16-15)2 +
(17-15)2
=0+2+4+2+4
= 12cm2/9
= 1.33 cm2 = Variance
Standard Deviation
Standard Deviation = the square root of the
variance.
For the corn example the variance was 1.33, so
the standard deviation is 1.15 cm.
See figure 25.2 on pg. 700
Discussion
• Agree or Disagree: Our school grading scale
should be based on the normal distribution
(fig. 25.2 on pg. 700).
– Write at least 1 paragraph explaining your
reasoning.
Assignment
• Read pg. 708-710
• Do pg. 722: C1, C3, and C7.
• Copy the meanings of the following variables
down in your notes:
– VG
– VE
– VGxE
– VG↔E
– VT