Meiosis and Gametogenesis

Vocabulary-style flashcards covering key definitions, stages, and concepts of meiosis and gametogenesis based on lecture material.

Meiosis

A specialized form of cell division occurring in germ cells where a diploid germ cell undergoes two nuclear divisions to yield four haploid daughter cells.

Meiosis I

The reductional division stage of meiosis that separates homologous chromosomes, producing two daughter cells with a haploid chromosome number ($N$).

Meiosis II

The equational division stage of meiosis where centromeres divide and sister chromatids of each dyad are pulled to opposite poles.

Pre-meiotic Interphase

The growth period prior to entering meiosis during which chromosome replication occurs during the S phase.

Prophase I

The longest and most complex phase of Meiosis I, occupying $85\text{--}95\times 10^{-2}$ of total meiotic time, subdivided into Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.

Leptotene

The first stage of Prophase I (also called leptonema) where chromosomes begin to condense into fine threads, nuclear volume increases, and homology search initiates.

Zygotene

The second stage of Prophase I (also called zygonema) where pairing between homologous chromosomes (synapsis) begins and ends, forming bivalents or tetrads.

Synapsis

The end-to-end pairing process between homologous chromosomes that occurs during zygotene.

Synaptonemal Complex

A proteinaceous structure formed during the zygotene stage that physically connects paired homologous chromosomes.

Bivalent

A structure composed of a pair of synapsed homologous chromosomes containing four chromatids; also referred to as a tetrad.

Pachytene

The third stage of Prophase I (also called pachynema) where synapsis is complete, chromosomes shorten and coil, and crossing over takes place between non-sister chromatids.

Crossing Over

The precise breakage, swapping, and reunion of DNA segments between non-sister chromatids of homologous chromosomes during pachytene, producing genetic recombination.

Chiasmata

Physical attachment points between homologous chromosomes where crossing over and genetic exchange took place.

Diplotene

The fourth stage of Prophase I (also called diplonema) where the synaptonemal complex breaks down and paired chromatids pull apart while remaining attached at chiasmata.

Diakinesis

The final stage of Prophase I characterized by maximum condensation of chromosomes, disappearance of the nucleolus and nuclear envelope, terminalization of chiasmata, and spindle assembly.

Terminalization

The movement of chiasmata toward the ends of chromosomes as prophase I progresses into diakinesis.

Metaphase I

The meiotic stage where bivalents migrate to the metaphase plate with centromeres of homologous pairs positioned on either side.

Anaphase I

The stage of Meiosis I in which homologous chromosome pairs separate and move to opposite poles while sister chromatids remain attached.

Telophase I

The stage of Meiosis I where homologous chromosomes complete migration to poles, nuclear envelopes reorganize around two chromosome groups, and nucleoli reappear.

Interkinesis

A brief stage between Meiosis I and Meiosis II (Interphase II) that is similar to interphase but lacks DNA replication.

Monad

An individual chromosome present at Telophase II consisting of a single combination of maternal and paternal genetic information.

Gametogenesis

The process of producing haploid sex cells (gametes) from germ cells.

Spermatogenesis

The process of producing male sperm cells (spermatozoa) in the testes via spermatocytogenesis and spermiogenesis.

Spermiogenesis

The metamorphic differentiation process that converts a large, spherical, non-motile spermatid into a small, elongated, motile sperm cell.

Oogenesis

The process of producing a mature haploid ovum from an oogonium in females, characterized by unequal cytoplasmic divisions.

First Polar Body

The small cell formed during the first unequal division of oogenesis that receives minimal cytoplasm but a haploid chromosome set.

Secondary Oocyte

The large cell produced after Meiosis I in oogenesis that retains nearly all of the cell's cytoplasm.

Ovum

The functional, large haploid female gamete rich in cytoplasmic enzymes, organelles, mRNAs, and metabolic substrates produced at the end of oogenesis.