Meiosis: Chromosome Reduction and Genetic Variation in Cell Division

What is the primary function of meiosis in sexually reproducing organisms?

To reduce chromosome number from diploid (2n) to haploid (n) and introduce genetic variation.

What is the starting and ending cell type in meiosis?

Starts with 1 diploid cell (2n) and ends with 4 haploid daughter cells (n).

What occurs during Prophase I of meiosis?

Synapsis of homologous chromosomes and crossing over occur; the nuclear membrane breaks down.

What happens during Metaphase I of meiosis?

Homologous pairs align at the equator, and independent assortment determines their orientation.

What is the outcome of Anaphase I in meiosis?

Homologues separate and are pulled by spindle fibers, still consisting of 2 chromatids.

What occurs during Telophase I of meiosis?

The nuclear envelope may reform, and cytokinesis may occur, resulting in 2 haploid cells (n).

What is Interkinesis in meiosis?

A short rest period between divisions where no DNA replication occurs, and chromosomes still have two chromatids.

What happens during Prophase II of meiosis?

Cells contain one chromosome from each homologous pair.

What is the significance of Metaphase II in meiosis?

Chromosomes align at the equator for the second division.

What occurs during Anaphase II of meiosis?

Centromeres split, sister chromatids separate, and move to opposite poles.

What is the result of Telophase II in meiosis?

Nuclear membranes form, and cytokinesis produces 4 haploid daughter cells.

How does crossing over contribute to genetic variation?

During Prophase I, homologues exchange segments, increasing genetic diversity.

What is independent assortment and when does it occur?

It is the random orientation of homologues during Metaphase I that contributes to genetic variation.

How does fertilization affect chromosome number?

Fertilization restores the diploid number by combining two haploid gametes (n + n = 2n).

What are the key differences between meiosis and mitosis?

Meiosis has 2 divisions producing 4 haploid, genetically variable cells; mitosis has 1 division producing 2 diploid, genetically identical cells.

When does crossing over occur in meiosis?

Crossing over occurs only during Meiosis I.