LIVETUTORIALS LEARNING LIBRARY
Foundations of One-Gene Inheritance
Separate genotype from phenotype and follow how allele pairs segregate in a simplified Mendelian inheritance model.
Overview
A diploid organism generally has two copies of a gene at a given locus in this simplified model, one inherited from each parent. Alternative forms of the gene are alleles. A homozygous genotype has matching alleles at the locus, while a heterozygous genotype has two different alleles.
During gamete formation, the allele pair segregates so that each gamete carries one allele at that locus. With equal segregation, a heterozygous Aa parent produces A and a gametes with equal probability. Combining possible parental gametes allows the offspring genotype probabilities to be calculated.
Complete dominance is an additional model assumption about phenotype. Under it, AA and Aa show the dominant phenotype while aa shows the recessive phenotype. Dominant does not mean better, stronger, more common or certain to increase in a population.
The linked tutorial distinguishes genotype and phenotype ratios, test crosses and independent offspring probabilities. Other inheritance patterns exist, so the simple ratios should only be used when the question's assumptions justify them.
References
Continue learning
- Monohybrid Crosses and Inheritance Probability
Use parental gamete probabilities to predict one-locus genotype outcomes and explain when the familiar phenotype ratio applies.