Genetics: DNA, Chromosomes, and Heredity Explained
Genetics: DNA, Chromosomes, and Heredity
DNA: A DNA fragment contains the information to make a protein.
Character: Attributes, morphological or physiological, define individual species.
Qualitative Traits: Determined by a single gene, clearly distinguishable.
Quantitative Traits: Influenced by several genes, showing gradual variation among individuals in a population.
Alleles: Various alternatives of a specific gene in a population.
Homologous Chromosomes: A pair of chromosomes containing the same genes in the same locations.
Homozygous: Presenting two identical alleles.
Heterozygous: An individual with different alleles for the same gene.
Genotype: The set of all genes present in an individual’s chromosomes.
Phenotype: The expression of certain genes from the genotype.
Dominant Inheritance: A gene with an allele whose effect prevails over others.
Codominant Inheritance: Two alleles of the same gene in a genotype display their individual effects.
Intermediate Inheritance: Two different alleles in a heterozygous individual express an intermediate or blended effect.
Mendel’s First Law (Law of Uniformity): The first filial generation, from crossing two purebreds for a specific trait, are all identical.
Mendel’s Second Law (Law of Segregation): Two alleles for the same trait do not blend in a hybrid but maintain their independence and separate during gamete formation.
Mendel’s Third Law (Law of Independent Assortment): Genes for different traits are transmitted separately and can appear in different combinations in offspring.
Autosomes: Chromosomes containing genes for somatic features common to both men and women.
Sex Chromosomes: Women have two X chromosomes of the same shape and length, while men have one X and one Y chromosome.
Sex-Linked Traits: Traits determined by genes located on sex chromosomes and transmitted with them.
Hemophilia: A disease characterized by the inability of blood to clot.
Color Blindness (Daltonism): A hereditary disease affecting vision.
Expression of Genetic Information: Encoded as a sequence of nucleotides in DNA, containing instructions for protein synthesis.
DNA consists of a sequence of four nucleotides with four bases (A, G, C, and T). Proteins are macromolecules made of amino acids.
The Genetic Code: The key relating nucleotides to amino acids, allowing us to understand the language of cells.
- Universal: The same genetic code governs all living beings.
- Degenerate: The genetic code relates 64 nucleotide triplets to 20 amino acids, meaning some amino acids are encoded by multiple triplets.
How are Genetic Instructions Deciphered? Protein synthesis from a gene occurs in two steps in eukaryotic cells:
- Transcription: Occurs in the nucleus.
- Translation: Occurs in the cytoplasm.
Messenger RNA (mRNA): Carries instructions to ribosomes for translation.
Transfer RNA (tRNA): Transports amino acids from the cytoplasm to the ribosome.
Ribosomal RNA (rRNA): A component of ribosomes, along with proteins.