In the 19th century, studies indicated that the nucleus contains mechanisms of inheritance.
Chromatin observed in nondividing cells, which condenses to form chromosomes during cell division.
Chromosomes contain genes, which are the basic units of inheritance, composed of DNA and proteins.
Approximately 20,000 to 25,000 human genes identified.
Errors in genes can lead to genetic diseases; over 23,000 individual human genetic traits cataloged.
One-third of pediatric inpatients suffer from genetic diseases, with common adult diseases (hypertension, diabetes, cancer) also linked to genetic factors.
Genetic testing and gene therapy are advancing to guide diagnosis and treatment of these diseases.
Identifies several thousand diseases with known genetic causes.
Carrier screening can determine whether individuals carry recessive disease alleles (e.g., cystic fibrosis, Tay-Sachs).
Prenatal diagnosis methods include:
Amniocentesis: Withdrawal of amniotic fluid to analyze fetal cells.
Chorionic Villus Sampling (CVS): Sampling of chorionic tissue, performed earlier than amniocentesis.
Preimplantation Genetic Diagnosis (PGD): Testing of embryos created through IVF.
Fetal DNA analysis in maternal blood: Non-invasive testing available as early as 6 weeks of gestation.
Presymptomatic testing available for hereditary diseases (e.g., familial breast or colon cancer).
Genetic testing helps predict drug efficacy and sensitivity to avoid adverse reactions (e.g., HIV treatment with Abacavir).
Genetic testing reveals mutations but many diseases exhibit incomplete penetrance (e.g., BRCA mutations linked to breast cancer).
Negative test results do not rule out the possibility of disease.
Gene therapy aims to correct mutations in DNA to treat diseases.
Includes somatic cell gene therapy; challenges include immune response and safe delivery of genes using vectors (often modified viruses).
Successful gene therapy treatments have reversed symptoms in conditions like severe combined immunodeficiency (SCID) and hemophilia B.
Ongoing research aims to develop safe gene therapies for more diseases.
DNA composed of nitrogenous bases (A, T, C, G) forming a double helix.
Codons consist of three base sequences that code for amino acids; 64 possible codons in total.
DNA replication involves unwinding double helix and complementary base pairing via DNA polymerase, which also has proofreading capability to ensure accuracy.
A mutation is an inherited alteration of genetic material.
Types of mutations include:
Base Pair Substitution: Replacement of one base pair with another.
Missense Mutation: Results in a different amino acid.
Nonsense Mutation: Introduces a premature stop codon.
Frameshift Mutation: Involves insertion or deletion that shifts the reading frame.
Mutagens can increase mutation frequency (e.g., radiation, chemicals).
RNA is synthesized from DNA in a process called transcription, producing mRNA.
mRNA undergoes splicing; introns are removed, exons rejoined.
Translation of mRNA directs polypeptide synthesis, involving tRNA and ribosomes.
Noncoding RNAs (like miRNAs and lncRNAs) play regulatory roles in gene expression.
Somatic cells are diploid (46 chromosomes), while gametes are haploid (23 chromosomes).
Chromosome abnormalities lead to major genetic diseases and are the leading known cause of intellectual disability.
Types of chromosome abnormalities include aneuploidy (e.g., trisomy, monosomy) and structural abnormalities (e.g., deletions, duplications).
Down syndrome (trisomy 21) is a commonly recognized chromosomal disorder resulting from nondisjunction.
Modes of inheritance identified include autosomal dominant, autosomal recessive, and X-linked conditions.
Pedigree charts are crucial for tracking genetic diseases across generations.
Autosomal Dominant Traits: Equal occurrence in sexes, no skipping generations, ~50% recurrence risk.
Autosomal Recessive Traits: Both sexes affected equally, often seen in siblings, ~25% recurrence risk.
X-Linked Recessive Traits: More common in males, skipped generations possible, can transmit through carrier females.
Genes on the same chromosome may be linked and inherited together due to proximity.
Crossing over during meiosis can lead to recombination, and frequencies of recombination give insights into gene mapping.
Genetic testing facilitates pinpointing disease-causing mutations and enhances genetic diagnosis.
Genes located on chromosomes; composed of DNA and specify proteins.
Mutation presence can alter genetic disease risk; various modes of inheritance exist.
Gene therapy is evolving to correct genetic disorders.
Genetic testing is valuable for diagnosis, treatment, and understanding disease inheritance patterns.