Question

Using what you know about the term mosaic, write a paragraph describing another biological mosaic

Answer 1

Answer:

.

Explanation:

In Caenorhabditis elegans, genetic mosaics have been generated, identified, and analyzed for the purpose of defining where in the animal a gene of interest must be expressed to cause a particular phenotypic effect. Most C. elegans mosaics that have been studied were homozygous mutant for a recessive mutation in all cells and carried additionally, in some cells, one or more copies of the wild-type allele of the same gene on an extrachromosomal element. Before mosaic analysis is undertaken, a mutant phenotype corresponding to the absence of the wild-type gene from all cells is analyzed and described. Some mutant phenotypes are described in whole-animal terms, such as uncoordinated movement, longer-than-normal lifespan, abnormal body shape, or inviability. Such traits can be analyzed in mosaic animals. The overall phenotypes are recorded for mosaic animals in which it is known which cells carry the wild-type gene and which do not, with the goal of establishing which cells must carry the wild-type gene to prevent the appearance of the mutant phenotype. The responsible cell or group of cells is referred to as the anatomical focus of the action of the gene with respect to the phenotype under study.

Over 75 genes have been analyzed in C. elegans genetic mosaics. Several examples of how mosaic analysis has contributed important insights into worm development were recently reviewed (Yochem et al., 2000; Yochem and Herman, 2003). Included were genes implicated in cell-to-cell signaling, with the functions of some genes assigned to the signaling cell and the functions of others assigned to the signal-receiving cell. Other examples in which anatomical foci were determined included genes affecting whole-animal phenotypes such as uncoordination, body size, and lifespan. A few additional examples are noted here.

Mutations that confer uncoordinated movement often affect the body-wall muscles or the nervous system. The nature of the cell lineage makes it possible quickly to distinguish these candidate cell types: all of the body neurons, except for two, descend from AB, a daughter of the zygote; and all of the body-wall muscles, with the exception of one, descend from P1, the other daughter of the zygote (Sulston et al., 1983; Figure 1). A thorough analysis of mosaics is, or course, required for rigorous determination of the actual focus of activity of the gene, which could be in a cell type other than muscle or neuron. In a recent analysis, the anatomical focus of unc-122 has been traced to muscle (Loria et al., 2004). The unc-71 gene, which regulates both motor-axon guidance and sex-myoblast migration, is thought to act cell nonautonomously for both functions. The gene is required in b

Answer 2

The fluid-mosaic model describes the plasma membrane of animal cells. The plasma membrane that surrounds these cells has two layers (a bilayer) of phospholipids (fats with phosphorous attached), which at body temperature are like vegetable oil (fluid). And the structure of the plasma membrane supports the old saying, “Oil and water don’t mix.”

Each phospholipid molecule has a head that is attracted to water (hydrophilic: hydro = water; philic = loving) and a tail that repels water (hydrophobic: hydro = water; phobic = fearing). Both layers of the plasma membrane have the hydrophilic heads pointing toward the outside; the hydrophobic tails form the inside of the bilayer.

Because cells reside in a watery solution (extracellular fluid), and they contain a watery solution inside of them (cytoplasm), the plasma membrane forms a circle around each cell so that the water-loving heads are in contact with the fluid, and the water-fearing tails are protected on the inside.