Concept 13.3: Meiosis reduces the number of chromosome sets from diploid to haploid

Flashcards from Concept 13.3 of Pearson's Campbell Biology, Twelfth Edition.

Meiosis

A method of cellular reproduction preceded by the replication of chromosomes, taking place in two stages

• Results in four daughter cells with half as many chromosomes as the parent cell

• Reduces the number of chromosome sets from two (diploid) to one (haploid), producing four genetically differing cells

Mitosis

A method of cellular reproduction that conserves the number of chromosome sets

• Produces two cells genetically identical to the parent cell

Sister chromatid cohesion

The close association of sister chromatids as chromosomes duplicate before meiosis and sorting

• Cohesins are cleaved at the end of metaphase in mitosis

• Cohesins are cleaved along the chromosome arms in anaphase I (separation of homologs) and at the centromeres in anaphase II (separation of sister chromatids)

Cohesins

Proteins that hold together sister chromatids after interphase

• Nonsister chromatids are broken at precisely matching points

Synaptonemal complex

A zipper-like structure that holds the homologs together tightly in prophase I

Synapsis

Process where DNA breaks are repaired and DNA is joined from one nonsister chromatid to the corresponding segment of another

Meiosis I

The first stage of meiosis with four phases:

• Prophase I

• Metaphase I

• Anaphase I

• Telophase I and cytokinesis

Prophase I

First stage of meiosis I where each chromosome pairs with its homolog and crossing over occurs at chiasmata

• Crossing over occurs for each sister chromatid within each chromosome, resulting in genetic variation for all four

Chiasmata

X-shaped regions on chromosomes where crossovers occur

Metaphase I

Second stage of meiosis I where pairs of homologs line up at the metaphase plate, one chromosome facing each pole

• Microtubules from the poles are attached to the kinetochore of each chromosome

Anaphase I

Third stage of meiosis I where pairs of homologs separate as one chromosome of each pair moves towards opposite poles

• Sister chromatids remain attached at the centromere and move as one unit toward the pole

Telophase I

Fourth and last stage of meiosis I where each half of the cell has a haploid set of duplicated chromosomes

• Each chromosome still consists of two sister chromatids

• Cytokinesis occurs simultaneously with this, forming two haploid daughter cells with either a cleavage furrow or cell plate forming

Meiosis II

The second stage of meiosis with four phases:

• Prophase II

• Metaphase II

• Anaphase II

• Telophase II and cytokinesis

Is very similar to mitosis

Prophase II

First stage of meiosis II where a spindle apparatus forms

• Chromatid pairs move toward the metaphase plate later in this stage

Metaphase II

Second stage of meiosis II where the sister chromatids are arranged at the metaphase plate

• Crossing over in meiosis I means the two sister chromatids are no longer genetically identical

• Kinetochores attach to microtubules extending from opposite poles

Anaphase II

Third state of meiosis II where the sister chromatids separate

• Each sister chromatid now moves as two newly individual chromosomes toward opposite poles

Telophase II

Fourth and last stage of meiosis II where the chromosomes arrive at opposite poles

• Cytokinesis occurs shortly after as nuclei form and chromosomes decondense