Genetics: A branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.
Focuses on the study of genes and how they vary and are inherited.
Understanding Traits
Trait: A physical characteristic or attribute of an organism, e.g., height, eye color, skin color, hair color.
Example: A girl with black hair, brown skin, and short height has these traits.
Cells and DNA
Cell: The smallest structural and functional unit of an organism.
Nucleus: Contains the chromosomes.
Chromosome: DNA wrapped around proteins, condensed to fit within the nucleus.
DNA is a long double helical structure that must condense to fit in the nucleus.
DNA and Chromosomes
DNA: A long, double-helical structure.
Chromosome: Formed when DNA is coiled and condensed around proteins.
Chromosomes allow DNA to fit into the small nucleus.
Genes
Gene: A segment of DNA that codes for specific proteins that express traits.
Not all DNA is coding; only certain segments are involved in protein coding.
Allele: One gene in a pair (homologous chromosomes) that codes for a specific trait.
Homologous Chromosomes
Homologous Chromosomes: Similar in size and structure, carrying genes for the same traits.
Example: Genes coding for height are present on homologous chromosomes.
Key Concepts
Locus: The specific location of a gene on a chromosome.
Heterozygous: An organism with one dominant allele and one recessive allele, e.g., Tt (where T is dominant for tall).
Homozygous: An organism with two identical alleles.
Homozygous Dominant: Two dominant alleles (e.g., TT) results in a tall phenotype.
Homozygous Recessive: Two recessive alleles (e.g., tt) results in a short phenotype.
Phenotype and Genotype
Genotype: The genetic makeup of an organism, indicating which genes are present.
Example: TT, Tt, or tt for height.
Phenotype: The physical appearance of an organism, determined by genotype.
Example: Tall (Tt, TT) or short (tt) plants.
Summary
This lecture covered the basics of genetics including definitions of key terms such as genes, traits, alleles, homologous chromosomes, locus, heterozygous, homozygous, genotype, and phenotype.
Understanding these concepts is crucial for studying inheritance and variation in organisms.