Question

In human females, when is meiosis initiated and completed?

A At birth, at ovulation
B At birth, it is continuous
C At puberty, at fertilization
D Prenatally, at ovulation
E Prenatally, at fertilization

Answer 1

In human females, meiosis is initiated prenatally and completed upon fertilization. The primary oocyte begins meiosis before birth and remains arrested until puberty, when hormonal changes resume the process each menstrual cycle. Ovulation releases the secondary oocyte, which only completes meiosis if fertilized.

Step-by-step explanation:

Initiation and Completion of Meiosis in Human Females

In human females, meiosis is initiated prenatally when the cell starting meiosis, known as the primary oocyte, begins the first meiotic division and is arrested during the prophase stage. This arrest continues until the individual reaches puberty. During each menstrual cycle, anterior pituitary hormones stimulate the development of follicles, leading to the completion of the first meiotic division. The process results in one large cell known as the secondary oocyte, and a smaller, typically non-surviving cell, the polar body. A secondary meiotic arrest then occurs at the metaphase II stage. The secondary oocyte is released from the ovary during ovulation. It is only if the secondary oocyte is fertilized by a sperm that meiosis is completed, resulting in a second polar body and the formation of a diploid zygote.

Therefore, in human females, meiosis is initiated prenatally and is completed upon fertilization.