Glossary
Allele
A specific version or form of a gene, located at a particular locus on a chromosome, that determines a specific trait.
Example:
For the gene controlling pea plant height, there are two common alleles: one for tallness and one for dwarfness.
Codominance
A genetic inheritance pattern where both alleles in a heterozygote are fully and simultaneously expressed, resulting in a phenotype that displays characteristics of both alleles distinctly.
Example:
In chickens, a black feather allele and a white feather allele can exhibit codominance, leading to offspring with both black and white feathers (erminette pattern).
Incomplete Dominance
A form of intermediate inheritance in which one allele for a specific trait is not completely expressed over the other allele, resulting in a blended or intermediate phenotype in heterozygotes.
Example:
When a red snapdragon flower is crossed with a white snapdragon, their offspring often display incomplete dominance by having pink flowers.
Multiple Alleles
A condition where a gene has more than two possible alleles within a population, leading to a wider range of potential genotypes and phenotypes.
Example:
The gene for coat color in rabbits can have four different multiple alleles, resulting in a variety of fur patterns like Himalayan or Chinchilla.
Non-Mendelian Genetics
Patterns of inheritance that deviate from the simple dominant/recessive rules established by Gregor Mendel, often involving more complex interactions between alleles or genes.
Example:
Understanding human blood types requires knowledge of Non-Mendelian Genetics because they involve multiple alleles and codominance, not just simple dominant-recessive pairs.
Phenotype
The observable physical or biochemical characteristics of an organism, resulting from the expression of its genotype and environmental influences.
Example:
A person's curly hair is their phenotype, which is the visible outcome of their genetic makeup.
Sex-linked traits
Traits determined by genes located on the sex chromosomes (X or Y), often showing different inheritance patterns and frequencies between males and females.
Example:
Hemophilia, a blood clotting disorder, is a classic sex-linked trait because the gene responsible is found on the X chromosome, affecting males more frequently.