How can gene regulation account for some of the phenotypic differences between organisms with similar genes? -Explain how interactions between external stimuli and gene expression result in specialization of cells, tissues and organs. Include two specific examples. -In Drosophila, development occurs as a result of the sequential expression of a variety of genes. Many of these are genes for transcription factors. The basic sequence or flow of development can be outlined as shown below: – Maternal effects genes (for example, bicoid) – Gap genes – Pair-rule genes – Segment polarity genes – Homeotic genes (or homeobox, Hox, genes) – Master regulatory genes (for example, myoD) -What does each type of gene control in the development of the fruit fly? – Based on your answers to the question above, if you wanted to produce a mutation that caused profound effects (drastic effects) on the overall development of the organism, where in the sequence would you introduce the mutation? Explain your answer. – What phenotype change(s) might you see if a developing fruit fly had a mutation in a gap gene? In a segment polarity gene?