m an adult frog transplanted into an enucleated egg can give rise to an entire tadpole. (more...) Further evidence that large blocks of DNA are not lost or rearranged during vertebrate development comes from comparing the detailed banding patterns detectable in condensed chromosomes at mitosis (see Figure 4-11 ). By this criterion the chromosome sets of all differentiated cells in the human body appear to be identical. Moreover, comparisons of the genomes of different cells based on recombinant DNA technology have shown, as a general rule, that the changes in gene expression that underlie the development of multicellular organisms are not accompanied by changes in the DNA sequences of the corresponding genes. There are, however, a few cases where DNA rearrangements of the genome take place during the development of an organism—most notably, in generating the diversity of the immune system of mammals (discussed in Chapter 24). Different Cell Types Synthesize Different Sets of Proteins As a first step in understanding cell differentiation , we would like to know how many differences there are between any one cell type and another. Although we still do not know the answer to this fundamental question, we can make certain general statements. 1. Many processes are common to all cells, and any two cells in a single organism therefore have many proteins in common. These include the structural proteins of chromosomes, RNA polymerases, DNA repair enzymes, ribosomal proteins, enzymes involved in the central reactions of metabolism , and many of the proteins that form the cytoskeleton . 2. Some proteins are abundant in the specialized cells in which they function and cannot be detected elsewhere, even by sensitive tests. Hemoglobin, for example, can be detected only in red blood cells. 3. Studies of the number of different mRNAs suggest that, at any one time, a typical human cell expresses approximately 10,000–20,000 of its approximately 30,000 genes. When the

# Why do cells vary in shape and function when they have the same genome and the same organelles? Tags: genomes, cell - Score: 5 - Views: 25880 - Answers: 3 - Answered: yes - Asked by: user4147 (2217 rep) - Asked: 2014-03-06 - Edited: 2014-03-06 - Site: biology ## Question Why do cells vary in shape and function when they have the same genome and the same organelles. For example: why do all cells have nuclei but red blood cell's don't; why can't the cells of a eye perform the function of the tongue; and the list goes on and on. If you say it is because of gene regulation, so then how does the RNA know to transcribe the specific genes that are necessary to that particular cell? ## Answers ### Answer by Chris (score: 11 [ACCEPTED]) Because cells are not only characterized by by their genetic material and other interior components, but also by the genes they express. Cells have to fulfill multiple different functions to be able to build complex multicellular organisms. Differently expressed genes lead to different proteins made in the cell, which leads to different morphology, shape or function. For example melanocytes in the skin are highly specialized cells which mostly make