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) 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, Chromosome structure 46 chromosomes are present in each human cell. Chromosomes are made up of DNA and histones. – 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: – 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.