Dr. Ahmed Fathalla Ibrahim
MITOSIS
DIFFERENCE BETWEEN MITOSIS & MEIOSIS
DEFINITION
The process of formation of mature male & female gametes.
• Spermatogenesis:Spermatogenesis: sequence of events by which the primitive germ cells (spermatogonia) are transformed into mature sperms or spermatozoa
• Oogenesis:Oogenesis: sequence of events by which the primitive germ cells (oogonia) are transformed into mature oocytes
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
SPERMATOGENESIS
SPERMATOGENESISSTAGES:• PROLIFERATION: each spermatogoniumspermatogonium divides by mitosis
into 2 daughter spermatogonia (with diploid number of chromosomes: 44 + XY)
• GROWTH: spermatogonium enlarges to form a primary primary spermatocytespermatocyte (with diploid number)
• MATURATION (BY MEIOSIS):1. 1st meiotic division: a reduction division by which a primary
spermatocyte divides into two secondary spermatocytestwo secondary spermatocytes (haploid number of chromosomes: 22 + X or 22 + Y)
2. 2nd meiotic divison: a process of mitosis without a normal interphase (without DNA replication) through which a secondary spermatocyte divides into two spermatidstwo spermatids (with haploid number of chromosomes)
• SPERMIOGENESIS: a process by which a spermatid is transformed into a mature sperma mature sperm (with haploid number)
SPERMIOGENESIS
SPERM
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%
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
OOGENESIS
OOGENESISSTAGES:• DURING FETAL LIFE:1. Proliferation: each oogoniumoogonium divides by mitosis into 2 daughter
oogonia (with diploid number of chromosomes: 44 + XX)2. Growth: oogonium enlarges to form primary oocyteprimary oocyte (with diploid
number). Primary oocytes begin 1st meiotic division & stop at prophase
• DURING EACH OVARIAN CYCLE (AFTER PUBERTY):1. 1st meiotic division is completed: a reduction division by which a
primary oocyte divides into one secondary oocyteone secondary oocyte (haploid number of chromosomes: 22 + X) & 1st polar body (degenerates)
2. 2nd meiotic divison begins: begins at ovulation, progresses only to metaphase and becomes arrested
• AFTER FERTILIZATION (IN THE FALLOPIAN TUBE)1. 2nd meiotic division is completed: 2ry oocyte divides into one one
mature ovummature ovum (haploid number) & 2nd polar body (degenerates)N.B.: NO PRIMARY OOCYTES FORM AFTER BIRTH IN FEMALESN.B.: NO PRIMARY OOCYTES FORM AFTER BIRTH IN FEMALES
OVULATION