| The phenotypically triple mutant female in this cross (top left) is heterozygous for the newly induced dominant mutation Antp, inherited from one parent, and the dominant marker mutations Sb and Ly, inherited from the other parent (parents not shown): Antp is therefore on one parental homolog and Sb and Ly are on the other. In order to find the position of Antp relative to the known markers Ly and Sb, the female is crossed with a genetically wild type male (top right). The eight different phenotypes seen in the progeny of this cross are shown together with the genotype of the maternally-derived chromosome above each fly (the chromosome inherited from the male parent has been omitted for clarity) and the numbers of each phenotype indicated on the right. Most of the progeny (166/200) inherit one of the maternal homologous chromosomes in its original form and have either legs instead of antennae and wild-type wings and bristles, or have normal antennae, thin wings and short bristles. However other phenotypes are seen in the progeny as a result of recombination between the maternal chromosomes during meiosis. Of these, since Antp is located slightly closer to Ly than to Sb, a higher proportion (18/200) have either legs in place of antennae and short bristles with normal wings, or wild-type antennae and bristles with thin wings, while 14/200 have legs in place of antennae and thin wings with normal bristles or normal wings and wild-type antennae with short bristles. A much smaller number (2/200) of progeny are either wild-type or mutant for all three traits; these represent double recombination events. From these data we can deduce that Antp is located between Ly and Sb, (14+2)/200= 8% or 8 centiMorgans from Ly and (18+2)/200 = 10% or 10 centiMorgans from Sb. |
