Drosophila may be monosomic for chromosome 4, yet remain fertile. Contrast the F₁ and F₂ results of the following crosses involving the recessive chromosome 4 trait, bent bristles: monosomic IV, bent bristles x diploid, normal bristles

Key Concepts

Monosomy

Monosomy refers to the condition in which an organism has only one copy of a particular chromosome instead of the usual two. In Drosophila, this can occur for chromosome 4, leading to a genetic imbalance. Despite this imbalance, organisms can still be fertile, as some genes may not be essential for reproduction, allowing for the continuation of the species.

Recessive Traits

Recessive traits are characteristics that are expressed only when an individual has two copies of the recessive allele. In the case of the bent bristles trait in Drosophila, the phenotype will only appear in individuals that inherit the recessive allele from both parents. Understanding how these traits are inherited is crucial for predicting the outcomes of genetic crosses.

F₁ and F₂ Generations

The F₁ generation is the first filial generation resulting from a cross between two parental (P) organisms, while the F₂ generation is produced by interbreeding F₁ individuals. Analyzing the phenotypic ratios in these generations helps in understanding inheritance patterns, especially when dealing with dominant and recessive traits, as well as the effects of chromosomal abnormalities like monosomy.