DNA & Genes
DNA: deoxyribonucleic acid, double helix, carries genetic information. Gene: segment of DNA coding for a protein. Genome: complete set of genetic material. Humans: 23 pairs of chromosomes (46 total) — 22 autosomes, 1 sex pair (XX female, XY male). Genotype: genetic makeup. Phenotype: observable traits. Allele: variant form of a gene. Homozygous: two identical alleles. Heterozygous: two different alleles. Dominant: expressed with one copy. Recessive: expressed only with two copies. Mutation: change in DNA sequence.
Inheritance Patterns
Autosomal dominant: one affected parent, 50% chance per child (Huntington disease, Marfan syndrome, familial hypercholesterolemia). Autosomal recessive: both parents carriers, 25% chance per child (cystic fibrosis, sickle cell, PKU). X-linked recessive: affected males, carrier females (hemophilia, color blindness). X-linked dominant: rare (hypophosphatemic rickets). Mitochondrial: inherited from mother only (Leber hereditary optic neuropathy). Multifactorial: genes + environment (diabetes, heart disease, cleft palate).
Nursing Implications
Family history: three-generation pedigree — identify patterns, at-risk individuals. Genetic testing: diagnostic, predictive, carrier, prenatal, pharmacogenomic. Genetic counseling: for at-risk individuals and families. Pharmacogenomics: drug response based on genotype (CYP2D6, warfarin sensitivity, clopidogrel resistance). Ethical, legal, social issues (ELSI): privacy, discrimination (GINA), informed consent, testing children for adult-onset conditions. Genetic discrimination: GINA protects employment and health insurance (not life, disability, long-term care). Resources: Genetics Home Reference, National Society of Genetic Counselors.
Important Notes
- Autosomal dominant: one affected parent gives 50% chance per child — Huntington disease, Marfan syndrome, familial hypercholesterolemia.
- X-linked recessive: affected males, carrier females — hemophilia, Duchenne muscular dystrophy, color blindness.
Clinical Tips
- Pharmacogenomics: CYP2D6 testing guides medication selection and dosing for codeine, tamoxifen, antidepressants.
- GINA (Genetic Information Nondiscrimination Act) protects against genetic discrimination in employment and health insurance.
Summary
Basic genetics for nurses includes understanding DNA, inheritance patterns, family history (pedigree), genetic testing, pharmacogenomics, and ethical considerations.
