Where I'm coming from in Bio2250 - Principles of Genetics
Genetics is traditionally taught ’Peas first, DNA later'. Facts and concepts are developed in the same order in which they were discovered historically. Genetics courses were taught for fifty years without any clear understanding of the molecular nature of the gene, and traditionally emphasized the analysis of crosses to understand the nature of heredity. This approach works well through the unraveling of the "Central Dogma" (DNA makes RNA makes Protein) by the early 1970s. In those days, we arrived at an understanding of protein synthesis, and the end of the course, simultaneously.
However, 2003 was the 50th anniversary of the discovery of the structure of DNA, and in 2013 the molecular revolution in biology continues to accelerate. The traditional approach requires the pretense that, when we talk about round and wrinkled peas, the student does not know about DNA, because Mendel didn't. Genetics and molecular biology have proliferated in so many directions that a single introductory course struggles to be comprehensive. Worse, there is an ever-widening stretch between what can be taught and what is required to understand molecular genetics. The current revolution in genomics have become technically so involved that it is difficult to present the complete logic, and we must skip to summaries of conclusions, and rely on databases for useful information.
Bio2250 reverse the traditional order: it
is taught "DNA
first, peas later". We begin
with an introduction to the molecular biology of DNA
structure and protein function, and build on this
foundation to introduce the behaviour of genes on
chromosomes and in crosses. A
course that begins, "DNA is a double-helix that is
replicated semi-conservatively...." (a standing broad jump over 50 years of
classical genetics) serves to remind most students of material
known at least since high school. The classical experiments of
Hershey & Chase, Watson & Crick, and Meselson & Stahl, and others, are
valuable introductions to scientific inference and problem
solving. They are however not crucial to understanding how DNA
functions. Likewise, it is necessary to understand in detail
how the Genetic Code
works, and less so to know how
Nirenberg & Khorana figured it out in the first place. An
initial grounding in the processes of molecular biology equips
us to talk about current topics such as DNA cloning,
Genetic Engineering, Biotechnology, and results from the
Human Genome Project. Selected experiments are still
analyzed in detail, to emphasize the problem-solving approach
in genetics. Most of molecular genetics is doing in a test
tube what goes on in a cell: if you understand nucleic acid
structure, base pairing rules, polynucleotide directionality,
and replication, you can understand vector insertion and
molecular cloning. With such a background, and an orientation
to modern experimental techniques, I hope that the course
will empower students to investigate further areas of
DIFFERENCE IN APPROACH MAY BE SUMMARIZED AS FOLLOWS.
The traditional method of teaching genetics is to understand phenotype in terms of genotype, and show the genotypic basis of phenotypes. The method of analyzing crosses is the traditional basis of "Genetics". That is, we teach that Peas have genes "for" alternative characteristics such as round vs wrinkled, or green vs yellow. In the same way, Humans have a gene "for" a genetic disease such as phenylketonuria. For each gene, we talk about in terms of one phenotype "dominating" another, and two alternative alleles being dominant or recessive. The nature of these alleles turns out to be due to variations the protein sequence, which is in turn a predictable consequence of particular changes in DNA sequences.
The modern method is to show
how DNA genotypes influence
pathways that produce characteristic phenotypes, the
consequences of mutations in DNA for alteration of the
outcomes of these pathways, and the interactions of the
alleles involved in terms of how they affect those phenotypes.
For example, we will see that in Peas, there is a DNA segment that codes
for a Starch Branching
Protein, which when modified causes a loss of turgor
pressure in seeds, and a "wrinkled"
appearance. Similarly, in Humans there is a gene that codes
for the enzyme Phenylalanine
Hydroxylase, that various alleles of this gene
produce higher or lower levels of PAH, and that the biochemical interaction
between the particular pair of alleles that an individual has
inherited determines whether or not that individual manifests
a disease called "Phenylketonuria".
We understand "dominant"
as descriptions of
a phenotype that is a consequence of a molecular genotype involving DNA and protein, rather than
intrinstic properties of bead-like genes on a string. The use
of molecular biology to understand the flow of information
from DNA to protein
to phenotype is sometimes called "Reverse Genetics"
because it reverses the traditional logic.
The Social Contract
1. I expect that all students will attend
Exams are based on lecture material, not on the text.
Your best preparation for exams is to do all of the assigned homework problems.
Other courses in Genetics at Memorial:
Population genetics is covered in Biol 2900 (Principles of Evolution & Systematics), another course in the core curriculum. My own research is an application of molecular genetics to evolutionary biology. You'll hear more about this later.
Molecular Biology of Nucleic Acids is covered in Biochemistry 3107 (Dr. Mulligan), which goes into greater depth on some of these same topics, from the perspective of a biochemist. Courses in Prokaryotic and Eukaryotic Gene Regulation are also taught through Biochemistry.
(Biol 4241) [Dr Carr] is
offered in the Winter Semester. This course considers
classic and current genetics experiments in detail, and cover
additional topics, including Immunogenetics, Cancer
Genetics, Molecular Evolution, and Quantitative
Genetics, and introduces modern topics such as Genomics
Text material © 2013 by Steven M. Carr