> Moving to the next question prevents changes to this answer. rog egg O a the s

Question

> Moving to the next question prevents changes to this answer. rog egg O a the second division begins in the animal region before the vegetal region before the first division first division has divided the vegetal cytoplasm completely ob the animal region contains fower, larger blastomeres than does the vegetal region c. the vegetal region contains more, smaller blastomeres than does the animal region mal region contains fewer, larger od the second division begins in the vegetal region betore the animal region berfore the first division has divided the vegetal oytoplasm completely Qu MacBook Air

Explanation / Answer

Cleavage in frog embryos is radially symmetrical and holoblastic .Throughout cleavage, the volume of the frog egg remains the same, but cells are divided into numerous cells. While the egg matures, it adds yolk to the vegetal cytoplasm, this yolk provides inhibition to cleavage. Because of this the animal hemisphere of the egg divides faster than the vegetal hemisphere.
The first division starts at the animal pole and gradually extends down into the vegetal region. As the first cleavage furrow is still continuing the cleavage in the vegetal hemisphere, the second cleavage has already started near the animal pole. So option a is true and d is wrong.
Third cleavage divides the frog embryo into four small animal blastomeres (micromeres) and four large vegetal blastomeres (macromeres). The micromeres in animal pole divide rapidly and the macromeres in vegetal pole divide slowly. Because of these difference in division rate as the cleavage progresses, the animal region get packed with small cells and the vegetal region get packed with small number of large, yolk-laden macromeres. So options b and c are wrong.
So right option is option a.

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