In this problem we will explore some of the many ways that mutations in two different genes can interact to produce different Mendelian ratios. Consider a hypothetical insect species that has red eyes. Imagine mutations in two different unlinked genes that can, in certain combinations, block the formation of red eye pigment yielding mutants with white eyes. In principle, there are two different possible arrangements for two biochemical steps responsible for the formation of red eye pigment. The two genes might act in series such that a mutation in either gene would block the formation of red pigment. Alternatively, the two genes could act in parallel such that mutations in both genes would be required to block the formation of red pigment.

Further complexity arises from the possibility that mutations in either gene that lead to a block in enzymatic activity could be either dominant or recessive. If the crosses is made between a wild type insect with red eyes and a true breeding white eyed strain with mutations in both genes. Such considerations yield the Pathways in series with dominant mutations in both genes, determine the phenotype of the F1 progeny and the expected phenotypic ratio of red to white eyed insects in the F2.

#Question id: 1370

#Unit 4. Cell Communication and Cell Signaling

H. V. Wilson worked with sponges to gain some insight into exactly what was responsible for holding adjacent cells together. He exposed two species of differently pigmented sponges to a chemical that disrupted intercellular junctions, and the cells of the sponges dissociated. Wilson then mixed the cells of the two species and removed the chemical that caused the cells to dissociate. Wilson found that the sponges reassembled into two separate species. The cells from one species did not interact or form associations with the cells of the other species.

How do you explain the results of Wilson's experiments?

#Question id: 1369

#Unit 4. Cell Communication and Cell Signaling

The following statements are made with reference to characteristics of glycosaminoglycans and proteoglycans, which are major constituents of extracellular matrix. Which one of them is incorrect?

#Question id: 1368

#Unit 4. Cell Communication and Cell Signaling

The following statements are made with reference to the characteristic of proteoglycans (major constituents of ECM). Which one of them is incorrect?

#Question id: 1080

#Unit 4. Cell Communication and Cell Signaling

 In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function?

#Question id: 1081

#Unit 4. Cell Communication and Cell Signaling

Which of the following is a type of local signaling in which a cell secretes a signal molecule that affects neighboring cells?

#Question id: 1082

#Unit 4. Cell Communication and Cell Signaling

Which of the following is a type of signaling in which a cells respond to substrate that they themselves release ?