Correct option is B
Statements Breakdown:
Statement A: "The cell fates are determined both by autonomous and conditional modes of specification."
Correct: In sea urchins, development involves both autonomous and conditional modes of specification. Autonomous specification refers to the intrinsic determinants within a cell, while conditional specification refers to the influence of neighboring cells on the cell's fate.
Statement B: "Large micromeres are conditionally specified."
Incorrect: Large micromeres in sea urchins are not conditionally specified. They are autonomously specified and have intrinsic determinants that guide their fate. Therefore, this statement is incorrect because large micromeres do not depend on the influence of neighboring cells but rather on the cytoplasmic content they inherit.
Statement C: "Large micromeres produce paracrine and juxtacrine factors that specify the fates of their neighbours."
Correct: Large micromeres indeed secrete paracrine and juxtacrine factors that influence the development of neighboring cells. These factors are crucial for cell signaling and help pattern the surrounding tissue. Therefore, this statement is correct.
Statement D: "β-catenin is not required for the specification of the micromeres."
Incorrect: β-catenin is required for the specification of micromeres. It plays a crucial role in the Wnt signaling pathway, which is essential for the specification of the micromeres during early sea urchin development. Therefore, this statement is incorrect.
Information Booster:
Autonomous vs Conditional Specification: Autonomous specification in sea urchins involves cells developing according to their intrinsic factors (often cytoplasmic determinants), while conditional specification involves interactions between cells that influence their developmental fate. Sea urchins exhibit both processes during their embryonic development.
Large Micromeres: These cells play a key role in early patterning in sea urchins. They secrete signaling molecules (paracrine and juxtacrine) that influence the development of neighboring cells, a fundamental process in the embryo's development.
β-Catenin's Role: β-catenin is required for the specification of micromeres. It is essential for the Wnt signaling pathway, which is necessary for early developmental decisions, especially for the formation of the micromeres.
Additional Information:
Option (a) A and B: While Statement A is correct, Statement B is not because large micromeres are autonomously specified, not conditionally specified.
Option (c) C and D: Statement D is incorrect because β-catenin is indeed required for micromere specification.
Option (d) B and D: Both Statement B and Statement D are incorrect, making this option incorrect.
