Incomplete Dominance & Codominance Flashcards

Incomplete Dominance & Codominance

• Complete Dominance: One allele completely masks another, resulting in a singular phenotype. For example, if a dominant allele represents red color and a recessive one represents white, the presence of the dominant allele will yield red flowers.

• Incomplete Dominance: Neither allele is fully dominant, leading to a blending of traits in the phenotype. An example is pink flowers resulting from red and white allele combinations.

• Codominance: Both alleles are expressed simultaneously and distinctly in the phenotype. For instance, speckled chickens display traits from both parent alleles without one masking the other.

Chromosomal Information

• Number of Chromosomes: Humans possess 23 pairs of chromosomes, totaling 46 in each somatic cell, with gametes containing only 23 individual chromosomes.

• Sex Chromosomes: These chromosomes determine gender and influence secondary sexual characteristics. Males and females typically have one X and one Y chromosome or two X chromosomes, respectively.

• X Chromosome: Significantly larger than the Y chromosome, it contains numerous genes, including those associated with colorblindness, a condition caused by a recessive allele on the X chromosome.

Genetic Makeup and Disorders

• Colorblind Female: Represented genetically as XcXc, inheriting two colorblind alleles from both parents results in colorblindness.

• Normal but Carrier Female: Genetically indicated as XcX, this individual possesses one allele for colorblindness (Xc) but also one normal allele (X), hence is not colorblind but can pass the trait to offspring.

• Colorblind Male: Denoted as XcY, possessing one colorblind allele (Xc) and one Y chromosome results in colorblindness, as males have only one X chromosome.

• Normal Male: Represented as XY, this male exhibits normal vision, carrying one X chromosome with the normal allele and one Y chromosome.

Genetic Concepts

• Multiple Alleles: Many traits are governed by more than two alleles, creating a greater genetic diversity within a population, although any individual can only inherit two alleles for a specific gene.

• Polygenic Inheritance: Characteristics are often influenced by several genes working in combination, leading to a variety of phenotypes across a spectrum rather than discrete categories.

• X-Linked Traits: These traits are associated with genes found on the X chromosome; they follow specific inheritance patterns and can result in conditions that are more prevalent in males due to the presence of a single X chromosome.