Meiosis and Genetic Recombination

Vocabulary practice flashcards covering meiosis phases, mechanics, chromosome dynamics, and origins of genetic variation from Concepts 13.1, 13.3, and 13.4.

Asexual Reproduction

A reproductive strategy utilizing mitosis to generate genetically identical offspring from a single organism, passing on $100\%$ of alleles rapidly and without courting or seeking a mate, but producing no genetic diversity.

Sexual Reproduction

A reproductive process typically involving meiosis and recombination that enhances genetic diversity within a population, wherein an organism passes along $50\%$ of its alleles.

Tetrad

A four-chromatid structure formed when homologous chromosome pairs align during prophase I of meiosis.

Crossing Over

The reciprocal exchange of genetic material between non-sister chromatids of homologous chromosome pairs during prophase I of meiosis.

Prophase I

The first meiotic stage where chromatin condenses into chromosomes, homologous pairs align into tetrads, crossing over occurs, the nuclear envelope breaks down into fragments, and centrosomes move toward opposite poles as spindle fibres develop.

Metaphase I

The meiotic stage where pairs of homologous chromosomes line up at the equator and spindle fibres attach to the centromeres with one fibre per chromosome.

Anaphase I

The meiotic stage in which spindle fibres shorten and pull homologous chromosome pairs apart toward opposite poles without separating the centromeres.

Telophase I

The phase following anaphase I where one complete set of chromosomes reaches each pole, chromatin may unpack and nucleoli may reform, and cytokinesis ensues to yield two haploid cells.

Prophase II

The initial stage of meiosis II occurring in haploid cells without an intervening S phase, during which chromatin recondenses into chromosomes, centrosomes replicate again, and the nuclear envelope disintegrates again.

Metaphase II

The meiotic stage during which individual chromosomes line up along the equatorial plate and spindle fibres attach to centromeres at a ratio of two fibres per chromosome.

Anaphase II

The stage of meiosis II where spindle fibres shorten and pull centromeres apart, causing sister chromatids to separate and take on a characteristic 'V' shape as they move toward opposite poles.

Telophase II

The final stage of meiosis II where chromosomes decondense back into chromatin, nucleoli reform, and cytokinesis divides the cytoplasm to form four haploid daughter cells.

Independent Assortment

A mechanism of genetic variation where tetrads orient and align randomly and independently of each other along the metaphase I plate.

Random Fertilization

The random union of any sperm (one of $2^{23}$ possibilities) with any ovum (one of $2^{23}$ possibilities), yielding $2^{46}$ possible combinations of alleles.

Cohesins

Protein complexes that hold sister chromatids together throughout cell division until anaphase separation.

Synaptonemal Complex

A zipper-like protein structure that physically holds non-sister chromatids together during synapsis in prophase I.

Synapsis

The pairing and physical association of homologous non-sister chromatids mediated by the synaptonemal complex during prophase I.

Chiasma

An X-shaped anatomical site where crossing over takes place between non-sister chromatids through single-copy breaks and DNA ligation.

Diplontic Life Cycle

A life cycle in which the dominant multicellular organism is diploid ($2n$) and produces haploid ($1n$) gametes via meiosis, which subsequently fuse during fertilization.

Haplontic Life Cycle

A life cycle in which the primary multicellular organism is haploid ($1n$), and the diploid zygote undergoes meiosis immediately after fertilization.

Haplodiplontic Life Cycle

A life cycle characterized by alternating between distinct multicellular haploid ($1n$) and multicellular diploid ($2n$) generations.