Lecture, chapter 5 - Inheritance of complex traits

Today we discussed one of the most important concepts in quantitative genetics.

We defined heritability and talked about some of its implications. We discussed the use of twin studies as tools the estimate heritability of different traits, and the importance of using both, monozygotic (MZ) and dizygotic (DZ) twin studies.

We discussed a few examples of multifactorial traits in humans: Skin color, IQ, and obesity.

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Announcement - Dates for lab quizzes

Lab quizzes will take place on the following dates, from 4:00-4:50 p.m.:

• Lab quiz 1: Tuesday, April 06 (week 5)
• Lab quiz 2: Tuesday, May 11 (week 10)

Each lab quiz will consist on 3-5 exercises like the ones that have been done in lab. A calculator will be required.

Rules:

• Each student will team up with a partner
• Students can talk ONLY to their partners
• Students are allowed to use notes and books
• The use of electronic devices (other than calculators) is NOT allowed (i.e. no cell phones, lap tops, net books, audio file players, etc.)

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Lecture, chapter 5 - Inheritance of complex traits

Today we continued chapter 5, on complex patterns of inheritance (polygenic and multifactorial).

We talked about how alleles in polygenic trait loci contribute to the phenotype, the characteristics of multifactorial traits, and the concept of regression to the mean.

We talked about the field of quantitative genetics; we discussed the kinds of questions it can answer and some of the most important concepts (phenotypic distribution, distribution of environments, norm of reaction)

Note:

We met in Meyer 113. We will meet in this room for the remaining lectures during this quarter.

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Lab 3 - Epistasis and hypothesis testing

Genetic corn

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In this lab we used genetic corn to test a prediction based on Mendelian principles, about the inheritance of two genes.

The color of corn kernels, although just one trait, is controlled by two separate genes (R and C) that affect pigmentation in the aleurone, which may or may not be pigmented. If transparent the color of the kernel will be yellow or white, and when pigmented it will be purple or red. In our case we only had purple and yellow kernels in cobs that were obtained as the F2 generation from a cross from double homozygote parent plants (RRCC x rrcc).

By doing a count of purple and yellow kernels, students were able to predict the phenotypic proportions of yellow and purple kernels. The predictions were compared to the observations and tested using a chi-square test, with a significance level of 5% (α=0.05).

When the hypothesis (observed values = expected values) was rejected, results were explained as the consequence of an epistatic interaction that prevented the R and C genes of showing the phenotypic proportions predicted by Mendelian inheritance.

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Lecture, chapter 4 - Pedigree analysisLecture, chapter 5 - Inheritance of complex traits

Today we finished chapter 4, on pedigree analysis.

We discussed cases in which the modes of inheritance we covered in previous lectures cannot be detected in a pedigree, because of complex gene and environmental interactions that prevent the phenotype of being fully expressed. Specifically we discussed age-related phenotypic expression, penetrance and expressivity. We provided examples of traits that show such phenomena.

We also started chapter 5, on polygenic inheritance and multifactorial traits.

We highlighted the difference between continuous and discontinuous phenotypic variation, and defined complex, polygenic and multifactorial traits.

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Lecture, chapter 4 - Pedigree analysis

Friday, March 19, 2010

Today we continued with our chapter on pedigree analysis.

We discussed several modes of inheritance

• autosomal dominant
• x-linked dominant and recessive
• y-linked (paternal)
• mitochondrial (maternal)

On Monday we will discuss cases of variations on gene expression.

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