Overview
This lecture introduces the fundamentals of genetics, focusing on the structure of DNA, the concepts of genes and alleles, and how genetic traits are inherited and expressed.
Chromosomes, DNA, and Genes
- Chromosomes are condensed forms of DNA found in the nucleus, especially visible during cell division (mitosis/meiosis).
- Humans have 46 chromosomes, organized in homologous (matching) pairs.
- DNA is the genetic code that determines all proteins and traits in the body.
- Genes are specific segments of DNA that code for particular characteristics (traits) like eye color or height.
Genes vs. Alleles
- A gene determines a characteristic, such as eye color or blood group.
- An allele is a variation of a gene, for example, blue, brown, or green eye color alleles.
- Homologous chromosomes carry alleles for the same genes in the same locations.
Inheritance of Traits
- Chromosome pairs consist of one maternal (from mother) and one paternal (from father) chromosome.
- Each gene exists in two copies (alleles), one on each chromosome of a pair.
- During meiosis, homologous chromosomes separate so only one allele is passed to each offspring.
Dominant and Recessive Alleles
- Dominant alleles are represented by capital letters (e.g., B) and are expressed if present.
- Recessive alleles are represented by lowercase letters (e.g., b) and are only expressed if both alleles are recessive.
- Possible allele combinations: homozygous dominant (BB), heterozygous (Bb), and homozygous recessive (bb).
- The expressed trait is called the phenotype; the allele combination is called the genotype.
Homozygous and Heterozygous
- Homozygous: having two identical alleles for a gene (BB or bb).
- Heterozygous: having two different alleles for a gene (Bb).
Key Terms & Definitions
- Chromatin Network — thread-like DNA structure in the nucleus visible during interphase.
- Chromosomes — condensed DNA structures, visible during cell division, carrying genetic information.
- Gene — segment of DNA coding for a specific characteristic.
- Allele — variation or type of a gene (e.g., blue vs. brown eye color).
- Homologous Chromosomes — chromosome pairs carrying alleles for the same gene locations.
- Dominant Allele — an allele expressed with only one copy present (capital letter).
- Recessive Allele — an allele expressed only with two copies present (lowercase letter).
- Genotype — the genetic makeup (allele combination) for a trait.
- Phenotype — the physical expression of a genotype.
- Homozygous — two identical alleles for a gene (dominant or recessive).
- Heterozygous — two different alleles for a gene.
Action Items / Next Steps
- Review meiosis and chromosome separation for better understanding of allele inheritance.
- Practice identifying genotypes and phenotypes from different allele combinations.
- Make flashcards for all key terms for effective study.