Gametogenesis Flashcards
(25 cards)
What is meiosis?
- A special type of cell division which divides the cell into four haploid cells
- Occurs in sexually reproducing cells
- DNA replication followed by two rounds of cell division producing four haploid cells
What is the difference between meiosis & mitosis?
Meiosis happens in the germ cells, while mitosis occurs in somatic cells
What is meant by aneuploidy?
Abnormal chromosome number causing the loss of the cell or miscarriage if it was in the baby
What are the general steps in meiosis?
1) Maternal and paternal chromosome joins (normal cell 2n & 2c “46 chromosomes”) 2n, 2c
2) Duplication in cell cycle G1, S & G2 (92 chromosomes) 2n, 4c
3) Enters meiosis 1 producing two haploid cells (1n, 2c)
4) Enters meiosis 2 forming 4 haploid cells (1n, 1c)
What is the difference in meiosis between males and females?
In spermatogenesis, there are 4 gametes produced while in oogenesis it’s one functional gamete + 3 polar bodies
What is meant by spermatogenesis?
The process of mature sperm formation, which occurs in the seminiferous tubules in the testis
What is the duration of spermatogenesis?
64 days
When does spermatogenesis start?
from puberty onwards (13-16yrs)
What are the steps in sperm formation?
1) Spermatogonium (46XY)
2) Primary spermatocyte (46XY)
First meiotic division (Meiosis 1)
3) Two secondary spermatocytes (23Y or 23X)
Second meiotic division (Meiosis 2)
4) 2 23X spermatids and 2 23Y
Spermatogenesis
5) Spermatozoa
Describe the phases of spermatogenesis (after the formation of spermatids)
1) The newly formed spermatid is spherical and has a Golgi apparatus
2) Small vesicles of the Golgi fuse giving rise to secretory pro-acrosomic granules, and centrioles start to migrate beneath the nucleus opposite to the granules
3) vesical fusion continues forming a large acrosomic vesicle containing dense acrosomic granules, the proximal centriole will give rise to the tail attachment point, the distal centriole will give rise to the developing axoneme (central portion of the tail)
4) The cap phase
5) The acrosomal phase
6) Maturation phase
Describe the cap phase
1) the remaining Golgi migrates to the caudal region, Distal centriole forms the tail (axoneme) which projects away from the nucleus and towards the seminiferous tubule lumen)
2) The acrosomic vesicle flattens, starts forming an outer acrosomal membrane and an inner acrosomal membrane, and starts accumulating acrosomal contents (enzymes)
Describe the acrosomal phase
1) The spermatid nucleus begins to elongate, and the acrosome starts covering the majority of the nucleus, A manchette (transient skirt-like structure, that surrounds the elongating head and serves as a guideline for the shape of the developing head) forms in the caudal region extending towards the developing flagellum
2) Neck & annulus are formed which will be the juncture between the middle piece and principal piece
What happens in the maturation phase?
1) Mitochondria form a spiral assembly around the flagellum which makes the midpiece
2) A post-nuclear cap appears (joins the neck to the acrosomal head) from the manchette microtubules
3) the annulus joins the middle piece and principal piece (rest of the tale)
What is the function of Sertoli cells (mother/nurse cell)?
- Nourishes the sperm cell throughout spermatogenesis
- Consumes the residual cytoplasm during spermatogenesis
What is oogenesis?
It is the process of mature ovum formation that occurs in the outer cortex of the ovary
- Prenatal maturation of oocyte (primary oocyte formation)
- Post-natal maturation of oocyte (formation of mature ovum)
When is the primary oocyte formed?
By the fifth month of fetal life which remains dormant in the prophase of meiosis I until puberty (10-13yrs)
What are the stages of oogenesis?
1) Oogonium
2) Primary oocyte (fifth month of fetal life stays in prophase of meiosis 1)
Before fertilization
3) formation of the secondary oocyte (at puberty arrested in meiosis 2 until fertilization) and a polar body which will be further divided into two polar bodies
After fertilization
4) secondary oocyte will form 1 polar body and a egg
- Polar bodies are degraded (3 polar bodies are formed)
- 1 X secondary oocyte wich will form the egg
What is the difference in gametogenesis between males and females?
1) Starts at puberty in men while in early embryonic development in females
2) Duration is 60-65 days per cycle till death, while, on the other hand, female gametogenesis starts from 10 to 50 years old
3) Males undergo 30-500 meiosis while females 20-30
4) males produce 4 spermatids per cycle, while females produce 1 ovum and 3 polar bodies
5) in one ejaculate there are about 100-200 million sperm cells, while females produce 1 ovum per menstrual cycle
What is the difference in the structure of sperms compared to the ovum?
1) Size
2) Motility (Ovum is motile, it’s moved by the ciliary action of the fallopian tube)
3) Membrane (Ovum is covered by the corona radiate and zona pellucida)
4) Cytoplasm (The ovum contains yolk granules for the nutrition of the embryo during the first week of development)
5) Chromosomes (Sperm: 23X or 23Y, Ovum: 23X only)
In what cell cycle phase karyotyping is possible?
Metaphase
How much DNA does a primary spermatocyte contain?
4N (96 chromosome)
A young woman enters puberty with approximately how many primary oocytes?
40,000
about how many primary oocytes will be ovulated over the reproductive life of a female?
480 (1 each month for 40 years)
What is meant by synapsis?
Pairing of homologous chromosomes
