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Review. Spermatogenesis, Oogenesis, Crossing Over, Imprinting---A Review. Primary germ cells migrate from the yolk sac to the ovaries or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells. Spermatogenesis.

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Review
Review

  • Spermatogenesis, Oogenesis, Crossing Over, Imprinting---A Review


Primary germ cells migrate from the yolk sac to the ovaries or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.


Spermatogenesis
Spermatogenesis or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.

  • Spermatogenesis, or sperm production, begins around puberty and continues for the remainder of a man's life

  • A young healthy man produces several hundred million sperm per day.


Spermatogenesis or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.


Oogenesis
Oogenesis or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.

  • During embryonic development, diploid cells in the ovaries called oogonia divide by mitosis to produce primary oocytes.  The primary oocytes are diploid.

  • Primary oocytes start meiosis.  They complete interphase and prophase I.  They are “frozen” at the end of prophase I and remain this way until the female reaches puberty.

  • A female is born with about 2 million primary oocytes.  By the time she reaches puberty, about 400,000 are left.


Oogenesis cont
Oogenesis cont…. or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.

  • After puberty, each month one of the primary oocytes is selected for ovulation (release from the ovary).  Just prior to ovulation, the primary oocyte is “unfrozen” and completes meiosis I, forms the first polar body, and is then frozen in meiosis II at metaphase II. 

  • After ovulation, if a sperm penetrates the secondary oocyte (egg) after it is released from the ovary, the secondary oocyte will be stimulated to complete meiosis II forming one more polar body and a mature egg.  The first polar body formed from meiosis one may also complete meiosis II to form another polar body.


Prophase I or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.


Fertilization takes place in the fallopian tubes
Fertilization takes place in the fallopian tubes or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.


Crossing over genetic variation
Crossing Over –Genetic Variation or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.


Crossing over
Crossing over or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.


Actual photograph of crossing over
Actual photograph of crossing over or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.


No crossing over during gametogenesis
No crossing over during gametogenesis or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.


Crossing over1
Crossing Over or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.

A

a

1. When does this happen in the formation of the egg and sperm?

2. Show the gametes formed using the letters “A” and “B” and “a” and “b”.

B

b


Imprinting
Imprinting or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.

  • Imprinting


Evidence
Evidence or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.

  • Uniparental embryos

  • Uniparental disomy

  • Differences in maternal and paternal gene function


Epigenetics and Disease or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.:

Genomic imprinting

Parent specific expression or repression of genes

or chromosomes in offspring.

So… even though two copies of a given gene are inherited,

one from each parent, only the maternal or paternal allele

is expressed.

The non-expressed allele is said to be “imprinted.”


Life cycle of an imprint
Life Cycle of an Imprint or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.


  • Wilms Tumor or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.

  • -Childhood Tumor of the kidney (nephroblastoma)

  • Accounts of 7% of all childhood cancers

  • -Caused by a defect in imprinting of the Insulin-like

  • Growth Factor 2 (IGF2) gene

  • IGF2 is usually only expressed from the paternal locus, ie

  • maternally imprinted

  • -Defects in imprinting that cause expression of the maternal

  • locus lead to cancer


Genomic imprinting and disease: or testes where they undergo mitosis and become oogonium or spermatogonium or remain germ cells.

Several diseases are associated with genomic imprinting

e.g.

Beckwith–Wiedemann syndrome

Prader–Willi syndrome

Angelman syndrome

Wilms Tumor

Fragile X syndrome

Myotonic dystrophy (congenital)


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