Biology – Variation | e-Consult

Discontinuous variation is variation that can be easily classified into distinct categories. It's often controlled by single genes with two alleles, where one allele is dominant and the other is recessive. The allele represents a variant form of a gene. Individuals inherit two alleles for each gene, resulting in a genotype (e.g., TT, Tt, tt). The phenotype is the observable characteristic resulting from the genotype (e.g., having a dominant thumb phenotype).

For thumb dominance, the dominant allele (T) results in a long thumb phenotype, while the recessive allele (t) results in a short thumb phenotype. Therefore:

• TT genotype: Long thumb phenotype
• Tt genotype: Long thumb phenotype (because T is dominant)
• tt genotype: Short thumb phenotype

The allele frequencies in the population determine the proportion of individuals with each phenotype. The genetic basis is the segregation of alleles during gamete formation and the random combination of alleles during fertilization, leading to the distinct phenotypic categories.