Lecture 6- Gametogenesis Flashcards
1
Q
- After colonising the gonad, germ cells:
A
- Proliferate by mitosis
- Reshuffle genetically and reduce to haploid by meiosis
- Cytodifferentiation into mature gametes
- Timing and scale varies between sexes
2
Q
oogenesis
A
- female: ovum
- very few gametes (around 400 in lifetime)
- intermittent production (1/month)
- 1/400th of reproductive potential
3
Q
spermatogenesis
- male: sperm
- huge number (200 million/ day)
- continous production
- essentially disposable cells
A
4
Q
2 main functions of meisosis
A
- Reduce the chromosomes number in the game to 23
- Ensures every gamete is genetically unique
5
Q
- MEIOSIS HAS …….. successive cells division:
A
2
- Meiosis 1 and 2
6
Q
meiosis produces
A
Produces 4 daughter cells
In females only one develops into a mature oocyte, others form polar bodies
7
Q
Genetic variation
Arises from:
A
-
Crossing over (meiosis 1)
- Exchange of regions of DNA between 2 homologous chromosomes
-
Independent assortment
- Random orientation of each bivalent along the metaphase plate with respect to other bivalents
- 8.4 million different varieties
- Random segregation
8
Q
spermatogensis describes
A
the production of male gametes
9
Q
spermatogensis overview
A
- Occurs in the testicle
- Sperm is formed in the seminiferous tubule (spermatogensis)
- Process of maturation of the sperm happens from the outside to the inside of the seminiferous tubules
- Diploids spermatogonium are found closest to the interstitium
- These become primary spermatocytes, then secondary spermatocytes and then the haploid spermatid is found at the centre of the seminiferous tubule
- These are then transferred through the lumen
- Leydig cells are found surrounding the seminiferous tubules in the interstitium
- Produce testosterone to promote spermaturation
- Process of maturation of the sperm happens from the outside to the inside of the seminiferous tubules
- Sperm is formed in the seminiferous tubule (spermatogensis)
10
Q
- Spermatids that emerge from the walls of the seminiferous tubules
A
- swim down the lumen of the seminiferous tubules and these tubules convalesce at the rete testis
- The rete testis concentrates the sperm and then pass onto the ductili efferentes to do the same
- The sperm emerge from the ductili efferentes into the head of the epididymis (storage tube for sperm)
- Upon ejaculation the sperm are released into the Vas deferens
11
Q
epididymis
A
(storage tube for sperm)
12
Q
Cells that aid spermatogenesis
A
- Sertoli cells
- Tight junctions form the blood testes barrier
- Leydig cells
13
Q
Sertoli cells
A
- spermatogenesis occurs supported by Sertoli cells.
- Nurture developing sperm
14
Q
- Tight junctions form the blood testes barrier
A
- Separates basal and adluminal compartment
- Provides correct environment for sperm to mature
- Prevent the immune system from recognising the genetic diversity of the sperm cell
15
Q
A
16
Q
raw material for spermatogenesis
A
spermatogonia
- Available for up to 70 years
17
Q
spermatogonia divide to
A
- Divide by mitosis to give rise to
- Ad spermatogonium (resting; reserve stock)
- Ap spermatogonium (active: maintain stock and from puberty onwards produce Type B spermatogonia which give rise to primary spermatocytes)
18
Q
Primary spermatocytes divide by meiosis giving rise to
A
- Secondary spermatocytes and then spermatids
- Each primary spermatocyte forms 4 haploid spermatids which differentiate (spermiogenesis) into spermatozoa
19
Q
spermiation
A
- release of sperm into seminiferous tubules
20
Q
Spermatogenic cycle (time) and waves (space)
A
- Not all stages in spermatogenesis are visible in a single cross section of seminiferous tubule
- Cells tend to appear in groups with same maturation stage
-
Spermatogenic cycle defined as time taken for reappearance of the same stage within a given segment of tubule (16 days)
- Diff stages in spermatogenesis are also ordered in space as well as time
- Each stage follows in an orderly sequence along the length of the tubule
- The distance between the same stage is called the spermatogenic waves