Question

Assertion Holoblastic cleavage with almost equal-sized blastomeres is a characteristic of placental animals.
Reason Eggs of most mammals, including humans are of centrolecithal type.

• A. extinction of these species from other regions
• B. continental separation
• C. absence of terrestrial route to these places
• D. retrogressive evolution

Answer 1

Answer: (C)

Eggs containing a small amount of yolk or without any yolk are known as micro-lecithal/ alecithal/oligolecithal/meiolecithal eggs. Such eggs are found in starfish, Amphioxus, Eutherian mammals including rabbit and human beings. In such egg, equal holoblastic cleavage takes plae in which equal or approximately equal-sized blastomeres are produced.