Fundamentals of Biology

Biochemical Genetics

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Session Overview

This session will explain how a collection of mutants with the same phenotype can be used to study a biochemical pathway. In effect, this session outlines how genetics can be used to study biochemistry. It includes a discussion of yeast as a model system. It outlines how to identify mutants with mutations in the same pathway, how to characterize the mutants into complementation groups, and how to use epistasis tests to infer details about a biochemical pathway. Learning Objectives To be familiar with the life cycle of yeast. To understand the difference between a genetic screen and a genetic selection. To understand why mutants with mutations in different genes can have the same phenotype. To understand what a test of dominance is and why it is performed. To understand what a test of complementation is and why it is performed. To understand what a test of epistasis is and why it is performed.

Session Activities

Lecture Video

For this session, watch the video lecture called “Genetics 3” by Prof. Eric Lander recorded in 2004. Then watch the first 7 ½ minutes of the lecture called “Human Genetics.”

• Genetics 3
• Human Genetics

Check Yourself

Question 1

A mutant haploid yeast cell that cannot grow without added histidine (mutant 1) is crossed to a wild-type haploid yeast cell (can grow without added histidine). The resulting diploid yeast cell CANNOT grow without added histidine. Which of the following statements is correct?

The mutant gene is dominant. close

The mutant gene is recessive. close

The mutant phenotype (cannot grow without added histidine) is dominant. check

The mutant phenotype (cannot grow without added histidine) is recessive. close

Check   Show Solution

The phenotype seen in the heterozygotic diploid is dominant.

Question 2

The phenotypes of two haploid tryptophan auxotrophs (trp1 and trp2) are both found to be recessive. These two mutants are crossed and the resulting diploid CAN grow on minimal media. Which of the following statements is correct?

The trp1 and trp2 mutations are in different genes. close

The trp1 and trp2 mutations are in the same gene. check

The trp1 and trp2 mutations do not complement. close

Check

Session Activities

Help Session Videos

First, watch the short video of Genny Gould explaining the concept of Complementation.

• Complementation

Next, watch Genny work a Complementation Problem (PDF) using fruit flies as an example.

• Complementation (Part II)

Practice Problems

• Problems (PDF)
• Solutions (PDF)

Further Study

Suggested topics for further study in an introductory-level Biology textbook

• Test of dominance
• Test of complementation
• Test of epistasis

Useful Links

• Complementation Test
• Epistasis: Gene Interaction and Phenotype Effects

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