Final answer:
The development and patterning of specialized cells in multicellular organisms are guided by gene expression and differentiation, with a pivotal role played by HOX genes and morphogens.
Step-by-step explanation:
The pathway that controls patterning of specialized cell types in tissues in most multicellular organisms is regulated by gene expression and involves a process called differentiation. During organogenesis, embryonic stem cells express specific sets of genes to differentiate into various cell types that make up tissues and organs. For instance, in the ectoderm, some cells will express genes that lead to their differentiation into skin cells. The regulation of differentiation and tissue patterning involves a complex interplay of cellular signaling cascades, and is crucially influenced by transcription factors, notably homeotic (HOX) genes and chemical signals known as morphogens that create a three-dimensional pattern for the organism's development.
The evidence for shared ancestry in this conserved strategy for communication between cells through regulation of transcription factors lies in the universal presence of HOX genes across a wide range of organisms. The conservation of this genetic mechanism across different species underlines its fundamental importance in the development of multicellular organisms.