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