Practice question

A sex-linked recessive lethal located on X chromosome impacts sexes differentially due to hemizygous male genotype. Males XY carrying single mutant X lack compensating normal allele and die during development, while heterozygous females XX possess normal allele that rescues viability, remaining as healthy carriers. Consequently adult progeny from carrier female x normal male show reduced male numbers, producing characteristic 2 females :1 male viable ratio and skewed sex ratio. Such lethals historically identified by Bridges using marked X chromosomes and balancer stocks maintaining lethal lines through heterozygous females.