Which of the following blastomeres contributes mostly to the nervous system of Xenopus?
b1
d2
a4
c4
c4
In Xenopus, the blastomere that contributes mostly to the nervous system is the animal hemisphere cells, specifically the dorsal animal blastomeres (D1.2 and D1.1). These cells give rise to the neural ectoderm, which eventually develops into the nervous system. Therefore, the correct answer would be d2.
To determine which blastomere contributes mostly to the nervous system of Xenopus, we need to understand the process of cleavage and differentiation in early frog development.
During early frog development, the fertilized egg undergoes cleavage, resulting in the formation of blastomeres. Blastomeres are the individual cells that make up the early embryo.
In Xenopus, the formation of the nervous system occurs through a process known as neurulation. Neurulation is initiated by the mesoderm cells, which induce the overlying ectoderm cells to form the nervous system.
Now, let's break down the options:
- b1: This blastomere is from the second cleavage of the embryo and does not contribute specifically to the neuroectoderm (which eventually gives rise to the nervous system).
- d2: This blastomere is also from the second cleavage and does not contribute specifically to the neuroectoderm.
- a4: This blastomere is from the fourth cleavage and is part of the animal hemisphere. The animal hemisphere does not contribute significantly to the formation of the nervous system.
- c4: This blastomere is from the fourth cleavage and is part of the vegetal hemisphere. The vegetal hemisphere is involved in the formation of the endoderm and not the nervous system.
Based on the options provided, none of the blastomeres mentioned (b1, d2, a4, c4) contribute predominantly to the nervous system of Xenopus.
To determine the blastomere that contributes mostly to the nervous system, we need to consider other cleavage stages or specific blastomeres involved in the development of the neuroectoderm.