Understanding Genes, Genotype, Phenotype, and Heredity
Genes are fragments of DNA that encode the synthesis of specific proteins. A gene is the unit of genetic information, composed of a unique sequence of nucleotides.
Genotype is the genetic makeup of an organism for a specific trait, determined by two genes, one from each homologous chromosome.
Phenotype is the observable manifestation of the genotype, the traits we see in an organism due to its genetic information.
Karyotype is a visual representation of all pairs of chromosomes, numbered, classified, and sorted by size and shape.
DNA is a molecule composed of four nucleotide units: cytosine, guanine, thymine, and adenine. Nucleotides consist of a phosphate group, a pentagonal sugar, and a nucleobase.
Mutation is a change in the nucleotide sequence of DNA. Even a single nucleotide change can cause serious problems for an organism. Pathogenic mutations can lead to diseases. These mutations can involve single base insertions, deletions, or changes in thousands of bases. Mutations can also contribute to the evolution of species.
Mendelian Inheritance
Uniformity Act: When crossing two pure breeds for a certain trait, the first generation offspring will be identical in both phenotype and genotype, and similar in phenotype to the parents.
Law of Segregation: During gamete formation, each allele of a pair separates, determining the genetic constitution of the gamete. Mendel observed this when crossing heterozygous individuals, noting a 3:1 ratio of yellow to green traits in peas.
Law of Independent Segregation: Different traits are inherited independently of each other, provided the genes are not linked or are widely separated on the same chromosome. The inheritance pattern of one trait does not affect the inheritance pattern of another.
Proteins
Protein molecules are essential for living organisms, formed by the union of amino acids. There are 20 different amino acids, allowing for an infinite number of possible proteins.
Functions of Proteins
- Protection and Structure: Providing consistency and impermeability, like collagen and keratin.
- Transport: Carrying substances, such as hemoglobin.
- Defense: Enabling defense mechanisms, like antibodies.
- Movement: Producing movement, like actin and myosin in muscles.
- Packaging: Packaging hereditary material, like histones.
- Signaling: Receiving signals, like cellular receptors.
- Catalysis: Encouraging or performing biochemical reactions, like enzymes.