In an embryo, the fourth and fifth stripes of the pair-rule genes are not formed normally, if embryo is homozygous mutant. In addition, the fifth and sixth stripes in embry do not form normally, if the gene Kni is mutant. This is because the expression of ftz gene needs the gene Kr in the formation of fourth and fifth stripes. The formation of fifth and sixth ftz stripes requires the function of Kni gene. Hence, in the absence of the Kni gene, the formation of fifth and sixth stripes will not be normal.
The loss of contiguous body segments in an embryo is resulted due to mutation in gap genes. They results in formation of a gap in the normal body plan. So, the development of a section of the organism needs the function of a gap gene. The gap genes found in the molecular level are expressed in the bands in the early embryo. These bands correspond to the segments, which are missing in the mutants.
The gap genes also encode for transcription factors. These transcription factors control the expression of pair-rule genes, which are responsible for segmentation. The gap genes are expressed under the control of maternal genes like Bicoid. Hence, they regulate each other to be expressed precisely.
The ftz pair-rule gene is called secondary pair-rule gene, which is regulated by primary pair-rule genes.