Question

The embryos of which one or more of the following animals show meroblastic cleavage?

• A. ( {Danio rerio} (zebrafish) )
• B. ( {Gallus gallus} (chicken) )
• C. ( {Synapta digita} (sea cucumber) )
• D. ( {Xenopus laevis} (frog) )

Hint:

Understanding the type of egg cleavage can provide insights into embryonic development and adaptations to different reproductive strategies across species.

Answer 1

The Correct Option is A

Meroblastic cleavage occurs in eggs that contain a significant amount of yolk. The cleavage furrows do not pass through the entire egg; instead, the division is incomplete.
Analysis of Each Option: (A) Correct: {Danio rerio} (zebrafish) eggs undergo partial, meroblastic cleavage due to the presence of yolk in the egg. (B) Correct: {Gallus gallus} (chicken) embryos exhibit meroblastic cleavage, characteristic of birds which have yolky eggs. 
(C) Incorrect: {Synapta digita} (sea cucumber), being an echinoderm, typically exhibits holoblastic cleavage, where the entire egg is divided. 
(D) Incorrect: {Xenopus laevis} (frog) embryos also show holoblastic cleavage despite the presence of moderate yolk. Conclusion:
Explanation: Meroblastic cleavage is generally seen in the embryos of animals with high yolk content in their eggs, which restricts the cleavage to the cytoplasmic portion of the egg, not penetrating the yolk mass. Both {Danio rerio} and {Gallus gallus} have egg structures that support this type of cleavage.