1. Which is true for amount of yolk and cleavage in egg of amphibian?
   (1) Mesolecithal and holoblastic cleavage
   (2) Isolecithal and holoblastic cleavage
   (3) Mesolecithal and meroblastic cleavage
   (4) Microlecithal and meroblastic cleavage

---

Introduction

Amphibian eggs are unique in their yolk composition and cleavage pattern, which are fundamental to their embryonic development. Understanding these features helps in grasping how amphibians develop from a fertilized egg into a complex organism.

---

Mesolecithal Eggs: Moderate Yolk Content

• Amphibian eggs have a moderate amount of yolk, concentrated mainly at the vegetal pole.

• This yolk serves as a nutrient reserve for the developing embryo.

• The presence of moderate yolk differentiates amphibian eggs from microlecithal eggs (with very little yolk) like those of mammals and isolecithal eggs (uniform yolk distribution) like echinoderms.

• The yolk distribution in amphibian eggs is telolecithal, meaning the yolk is unevenly distributed, concentrated more at one pole.

---

Holoblastic Cleavage

• Amphibian eggs undergo holoblastic cleavage, where the entire egg divides completely during early embryonic cell divisions.

• Despite the presence of yolk, the cleavage furrows pass through the whole egg, though cleavage in the yolk-rich vegetal pole is slower.

• This cleavage results in the formation of blastomeres and enables the embryo to develop efficiently.

---

Why Other Options Are Incorrect

• Isolecithal and holoblastic cleavage: Isolecithal eggs have little yolk uniformly distributed, typical of mammals, unlike amphibians.

• Mesolecithal and meroblastic cleavage: Meroblastic cleavage occurs in heavily yolked eggs (e.g., birds), where cleavage does not divide the whole egg.

• Microlecithal and meroblastic cleavage: Microlecithal eggs contain little yolk and usually exhibit holoblastic cleavage.

---

Biological Significance

The moderate yolk content in amphibian eggs provides sufficient nourishment without impeding complete cleavage. Holoblastic cleavage allows balanced cell division, crucial for patterned development in amphibians.

---

Conclusion

Amphibian eggs are characterized by mesolecithal yolk distribution and complete holoblastic cleavage, facilitating optimal development during early embryogenesis. These features distinguish amphibian eggs from those of other vertebrates and invertebrates and are essential for their reproductive strategies.

---

This article clarifies the egg type and cleavage pattern in amphibians, providing key insights into their developmental biology.

---

Final Answer:
(1) Mesolecithal and holoblastic cleavage