23. The zygote of C. elegans exhibits rotational cleavage. When the first two blastomeres formed (P1 and AB) are experimentally separated, the following outcomes may be possible:
    (A) The P1 cell in isolation generates all the cells it would normally make, showing autonomous
    specification.
    (B) The P1 cell in isolation generates all the cells it would normally make, showing conditional
    specification.
    (C) The AB cell in isolation generates a small fraction of cell types it would normally make, showing conditional specification.
    (D) The AB cell in isolation generates a small fraction of cell types it would normally make, showing autonomous specification.
    Which one of the above combination of statements is true?
    (1) A and C (2) B and C
    (3) B and D                                                      (4) A and D

In the early development of Caenorhabditis elegans, the zygote undergoes rotational holoblastic cleavage that produces two blastomeres known as AB and P1. These sister cells show different specification patterns revealed in transplantation and isolation experiments.

The P1 blastomere is autonomously specified. When isolated, it forms all the cell types that it normally gives rise to, demonstrating that its fate is predetermined by intrinsic factors. This autonomous specification aligns with mosaic development, where fate is set early and independent of external signals.

Conversely, the AB blastomere shows conditional specification, forming only a fraction of its normal cell types when isolated. This implies that AB’s fate is influenced by interactions and signals from neighboring cells, representing a regulative development pattern with developmental plasticity.

Based on experimental results, the true combination is:

• Statement (A): P1 cell in isolation generates all its normal cell types, indicative of autonomous specification.

• Statement (C): AB cell in isolation generates only some of its normal cell types, demonstrating conditional specification.

Thus, the correct answer is:

(1) A and C