Overview
This lecture introduces the basics of genetics, covering DNA structure, gene function, inheritance patterns, and important genetic concepts such as alleles, genotype, phenotype, penetrance, expressivity, and blood groups.
Cell Structure and DNA
- The cell is the basic unit of living organisms; groups of cells form tissues, organs, and systems.
- The nucleus is the control center of the cell, housing DNA.
- DNA (deoxyribonucleic acid) is composed of a sugar backbone (deoxyribose), phosphate, and nitrogenous bases.
- DNA is packed into 46 chromosomes in each somatic cell.
- DNA wraps around histones to form chromosomes.
DNA Functions and Genetics Overview
- DNA encodes proteins, including enzymes crucial for body functions.
- A gene is a piece of DNA coding for a specific protein.
- Each chromosome contains two chromatids; genes have specific locations called loci.
- DNA replication makes a copy of DNA; transcription converts DNA to RNA; translation makes proteins from RNA.
Alleles, Dominance, and Inheritance Patterns
- Each gene has two alternative forms (alleles), one from each parent.
- Dominant alleles mask the effect of recessive alleles (e.g., T for tall is dominant over t).
- Homozygous: both alleles are the same (TT or tt); Heterozygous: alleles are different (Tt).
- Phenotype is determined by the combination of alleles.
Penetrance and Expressivity
- Penetrance: the percentage of individuals with a genotype who express the phenotype.
- Expressivity: the degree to which a genotype is expressed in an individual (can vary in severity).
Genotype, Phenotype, and Blood Group Inheritance
- Genotype: genetic makeup (not visible); Phenotype: physical manifestation (observable trait).
- Blood group system: three alleles (IA, IB, IO); A and B are co-dominant, O is recessive.
- Four blood types exist (A, B, AB, O) based on the presence of antigens.
- Six possible genotypes: AA, AO, BB, BO, AB, OO.
Key Terms & Definitions
- DNA — Deoxyribonucleic acid, the molecule carrying genetic information.
- Gene — A DNA segment coding for a protein.
- Allele — Alternative form of a gene.
- Locus — Specific location of a gene on a chromosome.
- Homozygous — Identical alleles for a gene.
- Heterozygous — Different alleles for a gene.
- Penetrance — Proportion of individuals showing a phenotype.
- Expressivity — Variability of phenotype among individuals with the same genotype.
- Genotype — The genetic constitution of an organism.
- Phenotype — The observable traits of an organism.
- Co-dominance — Both alleles are fully expressed.
Action Items / Next Steps
- Review blood group inheritance patterns and allele dominance.
- Watch the next video in the genetics series for further study.