Genetics

Biochemical Genetics

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Session Overview

Genetics_sess_4.jpg

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.”

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.

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

Practice Problems

Further Study

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

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

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Learning Resource Types

theaters Recitation Videos
assignment_turned_in Problem Sets with Solutions
grading Exams with Solutions
theaters Lecture Videos