Fundamentals of Genetics, Inheritance, and Gene Expression
DNA Structure and Gene Function
DNA contains four nitrogenous bases: guanine, cytosine, tyrosine, and adenine. Cytosine always pairs with guanine, and timing always pairs with adenine. Base sequence mismatches cause mutations that render a gene non-functional, preventing the synthesis of its corresponding protein. A gene is a segment of linear or nonlinear DNA that encodes a polypeptide or protein, serving as the true functional unit of heredity compressed within chromosomes.
Alleles and Mechanisms of Inheritance
An allele is an alternate form of a gene, and genes consist of paired alleles. Humans receive chromosomes from the mother and from the father, totaling chromosomes ( pairs), whereas cattle and goats possess pairs ( total). Sex determination depends on inheriting an X chromosome from the mother and either an X chromosome (female) or a Y chromosome (male) from the father. Dominant alleles express their phenotype in both homozygous () and heterozygous () states, whereas recessive alleles express their phenotype only when homozygous ().
Genotype, Phenotype, and Environmental Interaction
A locus is the specific location of a gene on a chromosome, with multiple locations called locale. Genotype is an individual's hidden genetic makeup, whereas phenotype is the observable outward appearance. Phenotype is produced by the interaction between an individual's genotype and environmental factors, such as diet, weather, and lifestyle. When two heterozygous carriers () mate, hidden recessive traits can pair to produce homozygous recessive () offspring with a distinct phenotype.
Questions & Discussion
During the session, clarification was requested regarding how uppercase and lowercase letters represent dominant and recessive alleles in heterozygous combinations. A final inquiry was made asking if there were any remaining questions regarding homozygous, enterozygous, DNA, chromosome, allele, gene, and phenotype.