Biology: Genetics, Biology Genetics

Biology: Genetics, Biology Genetics Key Genetic Terms and Concepts 1. Dominant Allele - Definition: An allele that is fully expressed in the phenotype of a heterozygote, requiring only one copy to manifest the dominant trait. - Example: In the genotype Tt, the dominant allele is represented by the uppercase T. 2. Recessive Allele - Definition: An allele whose phenotype is masked in the presence of a dominant allele within a heterozygote. Two copies are needed to express the recessive trait. - Example: In the genotype Rr, the recessive allele is represented by the lowercase r. 3. Genotype - Definition: The genetic composition or set of alleles of an organism. - Examples: Genotypes may include PP, Pp, or pp. 4. Phenotype - Definition: The observable physical and physiological traits of an organism, which result from its genotype. 5. Punnett Square - Definition: A diagram used to predict the genotypic outcomes of random fertilization during genetic crosses between individuals with known genotypes. 6. Homozygous - Definition: Having two identical alleles for a particular gene. - Examples: RR or rr. 7. Heterozygous - Definition: Having two different alleles for a specific gene. - Example: Rr. 8. Incomplete Dominance - Definition: A mode of inheritance where neither allele is completely dominant. The offspring exhibit a phenotype that is a blend of the parental traits. 9. Codominance - Definition: A scenario where both alleles are equally expressed in the phenotype of a heterozygote, leading to distinct and separate expressions of both alleles. 10. Multiple Alleles - Definition: The presence of three or more forms of a gene that can code for a single trait. - Example: Human blood types (A, B, and O) illustrate this, with A and B being codominant to each other. 11. Sex-Linked Traits - Definition: Traits determined by genes located on sex chromosomes. Most commonly, these traits are X-linked, with the Y chromosome typically lacking the relevant alleles. - Examples: Color blindness, hemophilia in humans, and red/white eyes in fruit flies. 12. Pedigree - Definition: A genetic tool used to trace the inheritance patterns of genetic disorders within a family. ### Additional Concepts - Dominant Gene: A gene that suppresses the expression of another gene. - Sex-Linked Gene: An allele that is inherited on a sex chromosome. - Genetics: The field of study focused on how traits are inherited through the actions of alleles. - Complete Dominance: In the presence of a dominant and a recessive allele, the phenotype of the dominant allele prevails. - Homozygous Recessive: A genotype consisting of two lowercase letters (e.g., rr).