Meiosis

Epidemiology and Etiology:

· Males:

· Begins in puberty

· metaphase I and metaphase II occur without an intervening delay

· females:

· meiosis initiated in oocytes during fetal development

· meiotic arrest occurs after homologous chromosomes undergo synapsis and initiate recombination

· completion of the first division occurs in the sexually mature woman just before the oocyte is ovulated

· after completion of MI, the oocyte arrests at metaphase of MII

· second division is completed only after the egg is fertilized

Common sites:

·

Gross features:

·

Histologic features:

· Males:

· Each cell that undergoes meiosis produces 4 sperm

· Females:

· Each cell that enters meiosis produces only one egg and two or 3 polar bodies

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Molecular features:

· Prophase:

· Homologous chromosomes synapse and underglo recombination

· Meiosis I:

· Maintenance of physical connections between homologues until anaphase I

· Accomplished by sites of recombination (chiasmata)

· Segregation of homologous chromosomes from each other

· Some sort of physical constraint on centromeres of sister chromatids so that they form attachments to the same, rather than opposing, spindle poles

· Prophase I:

· leptotene: chromosomes begin to condense

· zygotene: homologs pair (telomere); Synaptonemal complexes form

· pachytene: crossing over occurs

· diplotene: homologs separate; remain attached at chiasma

· dictyotene: special stage in female meiosis where the process is arrested until prior to ovulation

· diakinesis: separation of homologs

· Meiosis II:

· Segregation of sister chromatids (analogous to mitosis)

Other features:

·

References:

· Hassold T, Hunt P. To err (meiotically) is human: the genesis of human aneuploidy. Nat. Rev. Genet. 2001;2(4):280-291.