Download Chapter 8: Genetic Epidemiology

Chapter 8: Genetic Epidemiology
Introduction
• Scientific advancement in genetics
– Mendel’s laws of inheritance
– Charles Darwin’s observations
– Discovery of DNA structure by Watson and Crick
– Human Genome Project
Genetics in a Nutshell (1 of 4)
Chromosome structure
• 46 chromosomes are
present in each human
cell.
• Chromosomes are made
up of DNA and histones.
Figure 8-1 Structure of a chromosome. The p arm is short
and q arm is longer; the ends of the chromosome are
called telomeres. The p and q arms meet at the
centromere.
Source: National Library of Medicine. Accessed July 10, 2010.
– RNA is produced from
DNA.
– Functional proteins are
produced from RNA.
– Proteins are made up of
amino acids.
Genetics in a Nutshell (2 of 4)
• Genetic code
– Three nucleotides form a codon (genetic code).
– Each codon is specific for an amino acid.
• Important enzymes and their function
– Topoisomerases are used to separate strands of
DNA.
– Polymerase helps replicate DNA.
– DNA-dependent RNA polymerase helps transcribe
DNA to RNA.
Genetics in a Nutshell (3 of 4)
• Genetic information transmission
– Transferred through sperm and ovum
• Epigenes
– Influence genetic expression without altering
nucleotide sequence in the genes
– Study of epigenes is known as epigenetics.
Genetics in a Nutshell (4 of 4)
• Single-nucleotide polymorphisms
– Result in insertion of a different amino acid in the
protein, changing the nature of the protein
• Haplotypes
– Unchanged segments of chromosomes
• Not affected by the exchange of genetic material
between paternal and maternal chromosomes found
elsewhere.
– Found in many people in the population
Gregor Johann Mendel’s Law of
Inheritance
• Experimented with inheritance in peas.
• Proposed existence of dominant and recessive
“factors” (later called genes).
• Inheritance of disorders can be:
–
–
–
–
–
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Autosomal dominant
Autosomal recessive
Autosomal trisomy
X-linked dominant
X-linked recessive
Y-chromosome linked
Charles Darwin’s Theory of Natural
Selection
• Based on observation of phenotypic variations
in animals and influence of environment on
selection of the species
• Individuals who best adapt to a changing
environment survive.
– And thereby contribute to evolution of species
Gene Mapping and the Human
Genome Project
• Global collaborative project from 1990 to
2003
• Mapped and sequenced entire human
genome
• Led to greater understanding of genetics
• Responsible for many innovations and
technological developments
DNA Biobanking
• Biobanks collect human tissue, blood, and
buccal smears.
– From patients with well-documented diseases
• Geneticists use the data to study links
between specific genes and disease.
• Pharmacogenetics also uses the data.
• Ethical, legal, and confidentiality issues arise.
Genetic Testing (1 of 2)
• Newborn screening
– Babies can be screened for hundreds of diseases
using a few drops of blood.
• Importance of early identification of diseases
– The progression of some diseases discovered can
be slowed.
Genetic Testing (2 of 2)
• Normal DNA repair mechanisms and gene
therapy
– Studying the former has led to the latter.
– In gene therapy, viruses are used to deliver genes
into targeted cells.
– Another approach, nanotechnology, attaches
genetic material to micromolecules and delivers to
target cells.
Genetic Counseling
• Impacted individuals should be informed of
likely future events in their disease process.
• Family education and testing may also be
appropriate.
• Ethical, legal, and discrimination issues are
involved.
– Appropriate agencies should be notified if such
issues are encountered.
Pharmacogenetics and
Pharmacogenomics
• Pharmacogenetics looks for genetic cause
when an unusual response to a drug is
detected in an individual.
• Pharmacogenomics links identified genetic
differences in populations to drug responses.
• Current pharmacogenetic research includes
cardiac, respiratory, and psychiatric
conditions.
Improving Public Health Through
Genetic Studies
• Breast cancer genes
– BRCA1 and BRCA2 genes have been discovered.
– Further research is needed.
• Mental health
– Genes involved in schizophrenia, Alzheimer
disease, and autism have been located.
• Exploration for predictors
– Examining subgroups may help predict some
genetic disorders.