Lecture, chapter 04 - Pedigree analysis in human genetics

Pedigree showing inheritance of an autosomal dominant trait
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We covered most of chapter 4, on pedigree analysis.

We discussed the several inheritance modes that can be studied by pedigree analyses (autosomal dominant and recessive, X-linked dominant and recessive, Y-linked, and mitochondrial), and we introduced the concepts of penetrance and expressivity.

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Lab 03 - Epistasis and hypothesis testing

Wednesday, December 09, 2009

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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Tissue layers on a corn kernel. When the aleurone

is transparent the kernel will show the color of

the endosperm (white or yellow)

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Lecture, chapter 3 - Mendelian genetics

Today we talked about Mendel's principles, the principle of segregation and the principle of independent assortment. We discussed how Mendel performed the experiments that lead him to formulate his principles and the implications of doing so at the time he did it. We also talked about the re-discovery of his work in the early 1900s, the connection of his findings with the discovery of chromosomes, mitosis, and meiosis, and finally set the stage to discuss some of the variations on Mendel's principles (cases other than complete dominance, multiple alleles, etc.)

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