Biology – The roles of genes in determining the phenotype | e-Consult

Gene: A gene is a unit of heredity that codes for a specific trait or characteristic. It's a sequence of DNA that provides the instructions for building a particular protein or RNA molecule.

Locus: The locus is the specific physical location of a gene on a chromosome. It's the address of the gene.

Allele: Alleles are different versions of the same gene. For example, a gene for eye colour might have alleles for blue, brown, or green eyes.

Dominant: A dominant allele is one that expresses its phenotype even when only one copy is present in the genotype. It masks the expression of the recessive allele.

Recessive: A recessive allele is one that only expresses its phenotype when two copies are present in the genotype. It is masked by the dominant allele.

Codominant: Codominance is a relationship between alleles where both alleles are expressed equally in the phenotype. Neither allele is dominant or recessive. For example, in the ABO blood group system, both the A and B alleles are expressed, resulting in AB blood type.

Linkage: Linked genes are genes that are located close together on the same chromosome. They tend to be inherited together, rather than assorting independently during meiosis. This means that recombination (crossing over) is less likely to occur between them.

Test Cross: A test cross is a genetic cross used to determine the genotype of an individual expressing a dominant phenotype. It involves crossing the individual with an homozygous recessive individual. The phenotypes of the offspring reveal the genotype of the dominant individual.

F1: The F1 generation is the first filial generation, produced by the cross of two true-breeding parents (homozygous). It represents the offspring of the first generation.

F2: The F2 generation is the second filial generation, produced by crossing individuals from the F1 generation. It represents the offspring of the second generation.

Phenotype: The phenotype is the observable characteristics of an organism, resulting from the interaction of its genotype and the environment. It's what we can see or measure (e.g., eye colour, height).

Genotype: The genotype is the genetic makeup of an organism, referring to the specific alleles it possesses for a particular gene. It's the actual DNA sequence.

Homozygous: An organism is homozygous for a gene if it has two identical alleles for that gene (e.g., AA or aa).

Heterozygous: An organism is heterozygous for a gene if it has two different alleles for that gene (e.g., Aa).