Video Transcript
How is the structure of a polar
body different from that of an ovum? (A) The polar body has more food
stores. (B) The polar body has very little
cytoplasm. (C) The polar body does not have a
nucleus. (D) The polar body has chromosomes
in pairs, diploid. Or (E) the polar body secretes
estrogen.
Let’s start by looking at some of
the keywords. An ovum is an egg cell that’s also
considered a gamete. As it was produced through meiosis,
it only contains half of the genetic material than a normal body cell. We call this a haploid cell. The polar body is a small
nonfunctional cell that is formed as the egg progresses through meiosis. The question asks about the
difference in the structure of a polar body and an ovum.
Let’s review the process of meiosis
in the egg cell to determine the answer. Meiosis consists of two stages of
division. During meiosis I, the primary
oocyte’s nucleus splits into two haploid daughter cells. Half of the genetic material of the
primary oocyte goes into a cell called the secondary oocyte, while the other half
goes into a polar body. The secondary oocyte actually
pauses during meiosis I and doesn’t continue until fertilization by a sperm
cell.
During fertilization, the secondary
oocyte completes meiosis to again have its genetic material. One half goes into the egg, which
can now pair with the sperm’s genetic material, while the other half is ejected into
another polar body. These polar bodies are tiny cells
that still contain nuclei with half the number of chromosomes, which makes them
haploid. However, they contain very little
cytoplasm and often are unable to divide and simply die.
So the main structural difference
between a polar body and an ovum is given by answer choice (B). The polar body has very little
cytoplasm.
