Question

Drosophila diploid 2n=8 tolerate trisomy and monosomy of their smolest chromosome 4 so all trisomic and monosomic for this chromosome are viable. However, nullisomic and tetrasomics for chromosome 4 are letal and this type of progeny never born.

Consider the segment polarity gene cubitus interruptus (ci), that affets cuticle characteristics (mutant has naked cuticle) and also alters the wing vein pattern. Consider that ci recessive mutations results in vein interraption in the wing while the ci+ wild type allows the normal vein pattern in the wing. Deduce the phenotypic proportions in the progeny of the following crosses involving trisomcs. What are the expected phenotypes and genotypes of the progeny from these different fly crosses?

Assume tat the presence ofone wild type ci+ allele is sufficient to confer the wild type wing vein pattern phenotype.

write the diagramm of the cross, genotype, phenotype

for F1 - genotypic and phenotypic ratio - # wild type (split as # diploid # trisomic or # ?) : # mutant (split as # diploid # trisomic or # ?)

1) ci+/ci+/ci x ci+/ci

2) ci/ci/ci x ci+/ci/ci

3) ci+/ci/ci x ci+/ci