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Health Studies
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Module 1
Sunday, November 27, 2005
6:05 PM
Module 1 - Introduction and Basic Principles
Classical (Mendelian) vs. Molecular Genetics
oCompare and contrast Mendelian and molecular genetics
With Mendelian genetics, we don’t care about understanding the biological nature
of the gene - we look at things from an abstract point of view
We do a lot of breeding studies and study genetic epidemiology (tracing
the path of a disease genetically)
With molecular studies, we try to understand the gene at a molecular level
We do a lot of genomic research and molecular biotechnology
Contributions of Genetics
oWhat are the 3 huge contributions of genetics to the world?
Agriculture, developmental biology, and health
oTalk more about each
We've been using it on wheat for over 7000 years
And on corn since the 1940's
Also on animal breeding and milk production
Developmental biology
This started in the 1920's with Thomas Hunt Morgan
He was into developmental genetics:
Here we study genes as a cause of development
And also cell differentiation…which ensures:
Continuity of species-specific traits
Individual variation (especially this one is necessary
for evolution)
His view was later modified to include consideration of:
Epigenetic view
We believe that gene expression varies
And we consider the effect of the environment on
genes (both cellular and external)
Gene repair mechanisms
These things respond to environmental stimuli
And they affect the rate of mutation
Well, let's start with health history…
In 1909, Garrod came up with "inborn errors of metabolism"
In the 1920's, we discovered the first inherited disease:
Both classical ("Mendelian") and molecular genetics are involved here:
Classical: we search for heritable TRAITS (outward stuff!)
Molecular: we make assumptions about the nature of genetic
contributions to health and manipulate genetic information
oWhat questions do we ask about genetics and health?
How are genes important to health?
i.e. How does it contribute to heart disease (stroke, hypertension),
diabetes, etc.?
How important are genes to health?

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Because we can eliminate the health problem but have the gene
(obviously) still present, so what's up with that?
Basic Principles of Molecular Genetics
Nucleic Acids
oWhat are the 2 kinds of nucleic acids?
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
oTalk about their structure
Each consists of polynucleotide chains
These are chains of nitrogenous bases on a backbone of sugar-
phosphate links (see Diagrams from website)
oTalk about the 2 classes of nitrogenous bases and where they are found
Purines: adenine & guanine (A & G)
Pyrimidines — cytosine (C) & thymine (T) (found in DNA)
OR cytosine (C) & uracil (U) (found in RNA)
oTalk about the 2 kinds of sugars and where they are found
oThere are also 2 sugars (pentoses):
2-deoxyribose in DNA
Ribose in RNA
oWhat are genes (basic definition)?
Genes are the basic entity of hereditary information
oTalk about how the genetic code is made up?
It is a sequence of bases
3 adjacent bases form a codon
Each codon codes for a specific amino acid
Thus, there are 64 possible codons
oBut how about the relationship between specific amino acids and codons?
There are 20 common amino acids (see Table from website)
Therefore, there is usually more than one codon for each amino acid
oTalk about amino acids and proteins
Amino acids are the basic building blocks of proteins (which are polypeptides)
A linear sequence of amino acids forms specific protein
There can be any number of amino acids comprising a protein
oNow tell me again what genes are?
A gene is a sequence of codons combining to produce a specific protein
oTalk about the 5 different kinds of proteins, and their functions?
Enzymes: catalyze chemical reactions (cell metabolism)
Transport: means of transporting molecules
Structural: material for cell and tissue structure
Regulatory: regulate cellular processes (e.g. hormones)
Antibodies: immune substances which recognize foreign substances
Central Dogma of Molecular Biology
oWhat is the central dogma of molecular biology?
DNA --transcription--> RNA --translation--> protein
oWhat are the 2 ways in which genetic information can flow?
DNA -> DNA (intergenerational transmission, aka DNA replication)
However, DNA replication is error-prone and it requires a repair
For example, it is susceptible to environmental events (affect ability for
DNA to repair itself)
DNA -> RNA -> protein (phenotypic expression)

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There are 2 stages (see Diagram on website):
Transcription: information from a segment of DNA is copied
onto mRNA
This segment provides the information to produce 1
Translation: amino acids are transferred to mRNA (by tRNA) to
form a protein
oWhere does all these genetic activity occur?
It always occurs in the cell!
DNA -> RNA in nucleus
RNA -> protein in cytoplasm
oWhat is the scope of the influence of JUST genetic information?
Genetic information acts only within the cell
All subsequent events resulting from these intracellular events (at the level of
tissues, organs, etc.) are at least partly dependent upon other factors
In fact, the Central Dogma of Molecular Biology is itself has been attacked
because of concept such as "regulator genes" which respond to environmental
events and thereby influence transcription and translation
oTalk about chromatin
Genetic material is contained in a substance called chromatin
The chromatin forms discrete units (called chromosomes) prior to cell division
oWhat is a karyotype?
Karyotypes consist of the chromosome complement and shape unique to a
particular species
oWhy is the knowledge of karyotypes essential in health?
Because we need to recognize chromosomal abnormalities
And also so that we can identify the location of individual genes (loci)
oSo what does the genome encompass? What does it NOT encompass?
The genome consists of all chromosomal DNA contained within all chromosomes
However, there is also mitochondrial DNA transmitted in mitochondria of egg
which is not considered part of the genome
No mitochondrial DNA from the sperm is transmitted to the egg, so each
individual receives their mitochondrial DNA only from their mother
oWhat are alleles?
Well, genes are inherited in pairs…and each gene of a particular pair is called an
allele of the other
If the alleles are identical, then we say that the individual is homozygous at that
Otherwise, we say that they are heterozygous
oWhat is the different between dominant and recessive traits?
A dominant trait is one in which the allele is expressed in both the homozygous
and heterozygous situations
A recessive trait is one in which the allele is expressed only if the alleles are
homozygous (it can be partially expressed if heterozygous)
oLook at original Ward notes to understand how the Punnett Square relates to
all of this
oWhat about the Y chromosome?
The Y chromosome is passed by the father to his sons, but it is not passed to his
This is termed holandric inheritance
It is not associated with any known syndromes
oHow about the X chromosome?
The X chromosome is passed from either parent to the daughters
But when they have a son, only the mother passes it
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