happens when a parent cell divides into two or more cells called daughter cells.
Cell Division
development of specialized cells that are organized into tissues and organs.
Differentiation
includes the physical processes that gives shape to an animal body and organ.
Morphogenesis
the process involved in the formation of matured gametes.
Gametogenesis
formation of the mature sperm cell in the testes
Spermatogenesis
production of mature egg cell in the ovary
Oogenesis
Phases of Gametogenesis
1.
Extra embryonic origin of the germ cells and their migration to the gonads.
2.
Increases in the number of cells by mitosis.
3.
Reduction in the number of chromosomes by meiosis.
4.
Structural and functional maturation of the reproductive cells.
- occurs in the testes
- begins between ages 11 to 15 years old and continues throughout the reproductive life of the male
- may result in 250 to 400 million cells per ejaculate
Spermatogenesis
Spermatogonia increase in number by simple mitosis to form cells known as spermatogonia; type-A and type-B.
Spermatocytogenesis
replicate DNA to have 46 double structured chromosomes to begin meiosis-1 and are called primary spermatocytes.
Type-B spermatogonia
primary spermatocytes
provides nutrition and pockets of support to developing spermatocytes.
Sertoli
differentiate into specialized cells known as sperms.
Spermatids
primary oocytes and nourishing cells layers around it.
Follicle
During the meiotic division of oogenesis, there is unequal divisions of the cells
Cytokenesis
*
a process whereby a sperm and an ovum combine to form zygote.
*
restores the diploid chromosome number, stimulates the secondary oocyte to complete the second meiotic division and metabolically activate the egg to undergo further development.
*
determines the chromosomal sex of the embryo.
Fertilization
Eggs are fertilized internally and deposited outside mother’s body to complete development.
bony fish, most reptiles, some cartilaginous fish, some amphibians, a few mammals, all birds.
Oviparity
Stages of Spermatogenesis
The sister chromatids of each chromosome separate from each other during meiosis II. The daughter cells are haploid spermatids.
The primary spermatocytes undergo meiosis I to produce haploid secondary spermatocytes in a duplicated state.
Each spermatid will then eventually mature into functional sperm cells.
Sertoli cells provide the cells with nourishment and molecular signals.
Undifferentiated germ cells called spermatogonia (diploid) undergo mitosis to produce daughter cells called primary spermatocytes.
3
2
4
5
1
*
occurs in the ovaries
*
starts in the embryo when primordial germ cells undergo mitotic divisions to produce diploid oogonia
*
a normal baby girl had about 2 million primary oocytes in her ovaries and by 7 years old, about 30,000 remains, her body reabsorbed the rest.
Oogenesis
Stages of Oogenesis
Stimulated by hormones, the follicle continues to grow, and the primary oocyte completes meiosis I. Resulting in the formation of a secondary oocyte (ends up with most of the cytoplasm) and the first of three polar body.
Ovulation then occurs releasing the secondary oocyte and the polar body
Primary oocytes have already entered meiosis I, but the nuclear division is arrested in a genetically programmed way.
Penetration of the sperm induces the secondary oocyte and the first polar body to complete meiosis II. There are now three polar bodies and one mature egg or ovum.
2
3
1
4
o
occurs outside the body, usually in water.
o
male and female release the sperm and egg in water.
o
large number of sperm and eggs are deposited to ensure successful fertilization
o
observed in fish, frogs and toads.
External Fertilization
occurs in the fallopian tube or oviduct of the female.
found in land vertebrates like reptiles, birds, and mammals.
Internal Fertilization
Young develop within mother and obtain nourishment directly from mother’s blood.
o
most cartilaginous fish, some amphibians, a few reptiles, almost all mammals.
Viviparity
Fertilized eggs are retained within mother to complete development, but all nourishment is obtained from yolk sac.
o
some bony fish (mollies, guppies, and mosquito fish), some cartilaginous fish, and many reptiles.
Ovoviviparity
Events in Fertilization
According to Carlson (1994) fertilization consists of the following sequential events:
Decondensation of
the sperm nucleus
Completion of
meiosis in egg
Prevention of
polyspermy
Fusion of sperm
and egg
Metabolic
activation of the
egg
Penetration of the
Corona Radiata
The development
and fusion of male
and female
pronuclei
Attachment to and
penetration of the
zona pellucida
6
7
4
3
5
1
8
2
