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. Anatomical2. Physiological3. Behavioral4. 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