Jaron Gladstone Period 3

Meiosis Jaron Gladstone Period 3

G1 phase: The period prior to the synthesis of DNA. In this phase, the cell increases in mass in preparation for cell division. Note that the G in G1 represents gap and the 1 represents first, so the G1 phase is the first gap phase. S phase: The period during which DNA is synthesized. In most cells, there is a narrow window of time during which DNA is synthesized. Note that the S represents synthesis. G2 phase: The period after DNA synthesis has occurred but prior to the start of prophase. The cell synthesizes proteins and continues to increase in size. Note that the G in G2 represents gap and the 2 represents second, so the G2 phase is the second gap phase.

Meiosis 1

In prophase I the chromosomes become visible. However, unlike prophase of mitosis, the two chromosomes combine or synapse to form tetrads. Tetrads are also known as bivalents because they contain two pairs of chromosomes. At this point the chromosomes cross over at points called chiasmata. Crossing over allows the chromosomes to exchange genetic material, allowing for more different combinations of genetic material. As in the prophase of mitosis the nuclear envelope disperses, the spindle moves into the center, and the tetrads become connected to the spindle fibers by kinetochores.

Meiosis 1

In metaphase I the tetrads are again arranged across the center by the movements of the kinetochores with the two centromeres opposite each other, but this time the sister chromatids will not be pulled apart as in mitosis.

Meiosis 1

In anaphase I the chromatids holding the chromosomes together loosen. The two homologous chromatids of each tetrad are separated into separate poles. Since the chromosomes from each parent can go into either pole this is another means to increase genetic diversity.

Meiosis 1

In this phase, like in mitosis the chromosomes are moved into opposite poles and the nuclear envelope reforms and the spindle is broken down. Remember that there are two chromosomes, not one as in mitosis.

Meiosis 1

The division of the cytoplasm and the plasma membrane following the division of the nucleus resulting into two daughter cells, each having its own nucleus and cytoplasm surrounded by a plasma membrane.

Meiosis 2

In meiosis the cell goes directly from telophase I to prophase II without the interphase. In prophase II the nuclear envelope is again dissolved and the spindle is set up again. Prophase II is identical to prophase of mitosis except that there is half the amount of chromosomes.

Meiosis 2

Again the chromosomes move into the center and line up. Now there are two chromosomes, instead of two tetrads, so that the chromatids will split off this time.

Meiosis 2

The kinetochores move towards the poles, splitting up the sister chromatids.

Meiosis 2

In telophase II the chromatids concentrate in the poles and the nuclear envelope is reformed and the spindle again is dissolved. The cells divide for the last time, leaving a total of four haploid cells, which have half the chromosomes of a diploid cell. Unlike the daughter cells from mitosis, the daughter cells produced here cannot immediately cycle back to interphase.

Meiosis 2

The division of the cytoplasm and the plasma membrane following the division of the nucleus resulting into four daughter cells, each having its own nucleus and cytoplasm surrounded by a plasma membrane.