meiosis shs

meiosis

is the process of division of gametes (reproductive cells), specifically the female egg and the male sperm.

meiosis I; meiosis II.

_ is a process where the sex cell divides twice; hence, _ and _

Meiosis I

begins with one diploid parent cell and ends with two haploid daughter cells, halving the number of chromosomes in each cell; halving the number of chromosomes in each cell; includes crossing over or recombination of genetic material between chromosome pairs.

Prophase I

Similar to the events in the mitotic prophase, the replicated chromosomes in _ become thicker and shorter.

Prophase I

The cell prepares for division; the nucleoli disappear; the nuclear membrane disintegrates and spindle fibers begin to form. Each chromosome is composed of two sister chromatids held together by a centromere called dyad.

dyad

In prophase 1, the cell prepares for division; the nucleoli disappear; the nuclear membrane disintegrates and spindle fibers begin to form. Each chromosome is composed of two sister chromatids held together by a centromere called _

Prophase I

Homologous chromosomes (each consisting of two sister chromatids) pair up through a process called synapsis, forming a tetrad (four sister chromatids).

Prophase I

During synapsis, genetic material is exchanged between homologous chromosomes in a process called crossing over. This increases genetic diversity.

chiasmata

Prophase I.

During crossing over, non-sister chromatids from homologous chromosomes swap sections of DNA at points called _. These _ hold the chromosomes together and mix genetic material.

1. Leptotene

2. Zygotene

3. Pachytene

4. Diplotene

5. Diakinesis

Prophase I of meiosis is divided into five major stages, each with specific events:

Leptotene

Chromosomes begin to condense and become visible as long, thin threads; they also start to attach to the nuclear envelope.

Zygotene

Homologous chromosomes pair up through a process called synapsis; The paired chromosomes form structures called tetrads.

Pachytene

Crossing over occurs, where non-sister chromatids exchange genetic material; Chiasmata form at the points where crossing over takes place.

Diplotene

Homologous chromosomes start to separate, but they remain connected at chiasmata; Chromosomes become more distinct and visible.

Diakinesis

Chromosomes condense fully and are prepared for separation; The nuclear envelope breaks down, and spindle fibers form in preparation for metaphase I.

Metaphase I

At this stage, tetrads are moved by the spindle to the equator of the cell. The homologous pairs of chromosomes remain together

Metaphase I

Spindle fibers increase in number; the kinetochore of the chromosomes will attach to facilitate movement.

Anaphase I

• Homologous chromosomes separate and migrate toward opposite poles of the cell.

• the sister chromatids remain attached at their centromere

Telophase I

The two daughter cells are completely divided; Nuclear membranes reform around each set of chromosomes at opposite poles.

Telophase I

The cell undergoes cytokinesis, resulting in two non-identical daughter cells, each containing half the number of chromosomes (haploid) but still consisting of sister chromatids.

Interkinesis I

• a short pause between meiosis I and meiosis II.

• similar to the interphase of mitosis, however, there is no replication of the chromosomes

Preleptonema

early prophase of meiosis, chromosomes are extremely thin and hard to observe

Meiosis II

• one chromatid of each goes to opposite poles.

• separates sister chromatids, resulting in four genetically unique haploid cells, each containing one set of chromosomes. These haploid cells can become gametes (sperm or eggs) in sexual reproduction.

Prophase II

chromosomes condense again; the nuclear membrane breaks down (if it had reformed), and spindle fibers form.

Metaphase II

Similar to metaphase I, chromosomes line up at the equatorial plate; spindle fibers attach to the centromeres of the sister chromatids from opposite poles.

Anaphase II

The sister chromatids are finally pulled apart by the spindle fibers and move to opposite poles of the cell.

Telophase II

Chromatids reach the poles and decondense; nuclear membranes reform around each set of chromosomes; cytokinesis divides the cytoplasm, resulting in four haploid cells.