Following statements are regarding to signals that regulate axis extension in chick embryos.

A. In the stage 10 chick embryo, Fgf8 inhibits expression of the retinoic acid (RA) synthesizing enzyme Raldh2 in the presomitic mesoderm and the expression of the RA receptor RARβ in the neural ectoderm, thus preventing RA from triggering differentiation in the caudal-lateral epiblast cells and the caudal-most paraxial mesoderm.

B. Fgf8 inhibits Sonic hedgehog (Shh) expression in the neural tube floorplate, controlling the onset of ventral patterning genes.

C. FGF signaling is also required for expression of Delta1 in the medial portion of the caudal-lateral epiblast cells and promotes expression of Wnt8c.

D. Fgf8 decays in the caudal paraxial mesoderm, Wnt signaling, most likely provided by Wnt8c, now acts to promote Raldh2 in the adjacent paraxial mesoderm. RA produced by Raldh2 activity expresses Fgf8 and Wnt8c.

Which of the following statements are correct?

TLS Online TPP Program

#Question id: 33480

#Unit 2. Cellular Organization

Finding: The overall degree of divergence between two homologous exons in related genes corresponds to the differences between the polypeptides.

Reason: Overall degree of divergence between two homologous exons is mostly a result of base substitutions.

TLS Online TPP Program

#Question id: 33481

#Unit 2. Cellular Organization

A. In homologous introns, the pattern of divergence involves both changes in length.

B. Divergence in introns is due to deletions and insertions and base substitutions. 

C. Introns are slowly evolve while exons much more rapidly 

D. When a gene is compared among different species, there are instances where its exons are homologous but its introns have diverged so much that very little homology is retained.

TLS Online TPP Program

#Question id: 33482

#Unit 2. Cellular Organization

Find true and false statements

A. In general, mutations occur at the same rate in both exons and introns, 

B. Exon mutations are eliminated more effectively by selection.

C. Introns may more freely accumulate point substitutions and other changes.

TLS Online TPP Program

#Question id: 33483

#Unit 2. Cellular Organization

Which of the following is correct

A. A set of homologous genes should share common features that preceded their evolutionary separation.

B. All globin genes have a common form of organization with four exons and one introns.

C. A gene family is defined as a group of genes that encode related or identical products as a result of gene-duplication events.

TLS Online TPP Program

#Question id: 33484

#Unit 2. Cellular Organization

When a complete gene is found within the intron of a larger “host” gene called as

TLS Online TPP Program

#Question id: 33485

#Unit 2. Cellular Organization

Most genes are uninterrupted in yeast, but most genes are interrupted in flies and mammals. Uninterrupted genes have