Biology - Human Reproduction Question with Solution | TestHub
Given below are two statements about embryonic development in human.
Statement (I): There is no growth phase between cleavages and the size of blastomeres is reduced.
Statement (II): As the size is reduced, the subsequent cleavages are faster than earlier ones.
In light of the above statements, choose themost appropriateanswer from the options given below.
Options:
Answer:
Solution:
Statement (I) is correct: Cleavage refers to the series of rapid mitotic divisions that a zygote undergoes. During these divisions, the interphase is very short and lacks the growth phases ( and ). Because there is no growth phase between the divisions, the total volume of the embryo remains constant, and the large zygote is partitioned into increasingly smaller cells called blastomeres.
Statement (II) is incorrect: The rate of cleavage does not continuously increase as the size of the blastomeres reduces. In human embryonic development, the first cleavage is relatively long (taking about 30 hours), the next few take about 12 to 24 hours, and as development proceeds towards the blastocyst stage, the cell cycle eventually lengthens. The introduction of and phases (around the mid-blastula transition) causes the subsequent divisions to slow down rather than become faster. Therefore, it is incorrect to state that subsequent cleavages are faster than earlier ones due to size reduction.
Therefore, Statement (I) is correct but Statement (II) is incorrect.
Answer: Statement (I) is correct but Statement (II) is incorrect.
