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GAMETOGENESIS

GAMETOGENESIS. Dr. Ahmed Fathalla Ibrahim. MITOSIS. DIFFERENCE BETWEEN MITOSIS & MEIOSIS. DEFINITION. The process of formation of mature male & female gametes.

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GAMETOGENESIS

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  1. GAMETOGENESIS Dr. Ahmed Fathalla Ibrahim

  2. MITOSIS

  3. DIFFERENCE BETWEEN MITOSIS & MEIOSIS

  4. DEFINITION The process of formation of mature male & female gametes. • Spermatogenesis:sequence of events by which the primitive germ cells (spermatogonia) are transformed into mature sperms or spermatozoa • Oogenesis:sequence of events by which the primitive germ cells (oogonia) are transformed into mature oocytes

  5. SPERMATOGENESIS • AIM: formation of sperms with haploid number of chromosomes • SITE: in the seminefrous tubules of testis • DURATION: takes about two months • OCCURRENCE: starts at puberty & continues throughout life

  6. SPERMATOGENESIS

  7. SPERMATOGENESIS STAGES: • PROLIFERATION: each spermatogonium divides by mitosis into 2 daughter spermatogonia (with diploid number of chromosomes: 44 + XY) • GROWTH: spermatogonium enlarges to form a primary spermatocyte (with diploid number) • MATURATION (BY MEIOSIS): • 1st meiotic division: a reduction division by which a primary spermatocyte divides into two secondary spermatocytes (haploid number of chromosomes: 22 + X or 22 + Y) • 2nd meiotic divison: a process of mitosis without a normal interphase (without DNA replication) through which a secondary spermatocyte divides into two spermatids (with haploid number of chromosomes) • SPERMIOGENESIS: a process by which a spermatid is transformed into a mature sperm (with haploid number)

  8. SPERMIOGENESIS

  9. SPERM

  10. SEMINAL FLUID • SOURCE: secretions from seminal vesicles, prostate gland & bulbourethral glands • VOLUME: 3 – 5 ml • SPERM COUNT: about 100 millions/ml • MOTILITY: about 3mm/min, at least 70% of sperms should be motile • ABNORML FORMS: should not exceed 10%

  11. OOGENESIS • AIM: formation of secondary oocytes with haploid number of chromosomes • SITE: in the cortex of ovary • OCCURRENCE: starts during fetal life , becomes completed after puberty & continues till menopause

  12. OOGENESIS

  13. OOGENESIS STAGES: • DURING FETAL LIFE: • Proliferation: each oogonium divides by mitosis into 2 daughter oogonia (with diploid number of chromosomes: 44 + XX) • Growth: oogonium enlarges to form primary oocyte (with diploid number). Primary oocytes begin 1st meiotic division & stop at prophase • DURING EACH OVARIAN CYCLE (AFTER PUBERTY): • 1st meiotic division is completed: a reduction division by which a primary oocyte divides into one secondary oocyte (haploid number of chromosomes: 22 + X) & 1st polar body (degenerates) • 2nd meiotic divison begins: begins at ovulation, progresses only to metaphase and becomes arrested • AFTER FERTILIZATION (IN THE FALLOPIAN TUBE) • 2nd meiotic division is completed: 2ry oocyte divides into one mature ovum (haploid number) & 2nd polar body (degenerates) N.B.: NO PRIMARY OOCYTES FORM AFTER BIRTH IN FEMALES

  14. OVULATION

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