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JustinJakubisinRepo (Male reproductive structures from seminiferous…
JustinJakubisinRepo
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Spermatogenesis
Definition-
Spermatogenesis
Begins with the spermatogonia (diploid stem cell) that differentiate into diploid primary spermatocytes
First stage: Spermatogonium
one diploid cell that goes to Mitosis to differentiate into primary spermatocyte
Second Stage: Primary spermatocyte
one diploid cell that undergoes Meiosis I to become two secondary spermatocytes
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The process of Oogenesis
Definition- The process by which a diploid germ cell, an oogonium, in the fetal ovary becomes a haploid ovum in the adult after fertilization occurs.
First Stage of Oogenesis
OOgonia migrate from the yolk sac to the fetal ovary where further mitotic divisions occur.
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Second Stage of Oogenesis
Oogonia begin meiosis I (reductional division) to form diploid, primary oocytes that are located in primordial follicles. These primary oocytes arrest in prophase and are the only follicles present from birth until puberty, when selected follicles undergo a series of changes during each ovarian cycle, resulting in ovulation.
Third Stage of Oogenesis
Each month a cohort of primordial follicles is recruited into the ovarian cycle. These follicles pass through primary and secondary follicles stages and a single secondary follicle continues as the mature follicle which is ovulated.
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Fourth Stage of Oogenesis
A secondary oocyte is formed during the day preceding ovulation in each ovarian cycle. Stimulated by the LH surge, a primary oocyte in the Graafian follicle completes meiosis I to form a haploid secondary oocyte. This secondary oocyte begins meiosis II but arrests in metaphase; this is the oocyte that is ovulated.
Fifth Stage of Oogenesis
An ovum, a mature, haploid germ cell, is formed in the oviduct (completion of meiosis II) only after fertilization occurs.
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Meiosis
Definition-Meiosis
Duplicates it's chromosomes before undergoing this process. Produces haploid number (1N), halving the number of chromosomes. 2 divisions of primary sex cells result in 4 haploid gametes.
Prophase I
Chromatin condenses into chromosomes, spindle forms, nucleoli and nucleus disappear. Homologous chromosomes come together and intertwine (synapsis), each synaptic pair contains 4 chromatids (tetrad), it can exchange equivalent pieces of DNA (crossing over). which results in increased genetic diversity with in species. Sister chromatids are no longer identical.
Metaphase I
homologous pairs (tetrads) align at the equatorial plane. Attaches to a separate spindle fiber by its kinetochore.
Anaphase I
homologous pairs separate to opposite poles. (disjunction). Accounts for a fundamental mandelian law: each chromosome of paternal origin separates from homologue of maternal origin, thus daughter cells are random with respect to paternal origin.
Telophase I
nuclear membrane forms around new nucleus, still sister chromatids joined at centromere.
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