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, normal bristles x diploid, bent bristles.

Key Concepts

Monosomy

Monosomy refers to the condition where an organism has only one copy of a particular chromosome instead of the usual two. In Drosophila, being monosomic for chromosome 4 means that there is only one copy of this chromosome present. This can lead to specific phenotypic expressions, such as the potential for fertility despite the loss of genetic material, which is crucial for understanding the genetic outcomes in the given crosses.

Recessive Traits

Recessive traits are characteristics that are expressed only when an individual has two copies of the recessive allele. In the context of the bent bristles trait in Drosophila, this means that a fly must inherit the bent bristles allele from both parents to exhibit the phenotype. Understanding how these traits segregate during crosses is essential for predicting the phenotypic ratios in the F₁ and F₂ generations.

Genetic Crosses and Segregation

Genetic crosses involve mating individuals to observe the inheritance patterns of specific traits. The F₁ generation results from the initial cross, while the F₂ generation arises from self-fertilization or intercrossing of F₁ individuals. The principles of segregation, as described by Mendel, dictate how alleles are distributed to offspring, which is vital for analyzing the outcomes of the crosses involving monosomic and diploid individuals in the question.