Gametogenesis Flashcards
How is genetic variation introduced into meiosis?
- Crossing over.
- Independent assortment at Metaphase 1 and 2.
- Random segregation (alleles randomly distributed among the four gametes produced).
Describe the different types of spermatogonia in the testes.
Ad: These are a reserve stock and do not contribute to active spermatogenesis.
Ap: These are active stock and produce (from puberty onward) type B spermatogonia which give rise to primary spermatocytes and thus the process of spermatogenesis)
What is the difference between spermatogenesis and spermiogenesis?
Spermatogenesis is effectively the meiosis process giving spermatids.
Spermiogenesis is the process, supported by the sertoli cells, where the spermatids differentiate into spermatozoa.
What would you see if you took a cross section through a seminiferous tubule, thinking in the context of the stages of spermatid maturation?
Generally, cells appear in groups with other cells in the same stage of maturation. Not all stages of maturation would be represented at that level.
What is a spermatogenic cycle?
The time it takes - usually 16 days - for the same stage of maturation to re-appear within a given segment of the tubule.
What makes a spermatogenic cycle different from a spermatogenic wave?
Cycle is time between the same stage of development, wave is the distance from one set of cells in stage x and another also in stage x.
What term can we give the release of spermatids into the seminiferous tubule lumen?
Spermiation
Describe the course of a re-modeling spermatid as it passes into the epididymis. Where along this process does maturation complete?
Seminiferous tubules -> rete testis ->ductili efferentes -> epididymis. Maturation completes in the epididymis.
Describe the origins (and % constitution) of the constituents of semen?
2mL per ejaculate produced:
70% seminal vesicles (amino acids, citrate, clotting factors, fructose).
25% prostate: zinc and proteolytic enzymes.
2-5% sperm from testes.
Cowper’s Gland Mucus: Alkaline. Less than 1%.
What is sperm capacitation?
When sperm is released in the ejaculate its cap is covered with glycoproteins and cholesterol. Once the sperm is within the female reproductive tract a signalling pathway is initiated allowing sperm to undergo the acrosome reaction following binding to the zona pellucida.
How do oocyte numbers change in the lifetime of a female.
They peak at about 7 million mid-gestation. After this, atresia occurs leading to the death of many oogonia and primary oocytes. Most oogonia are gone by 7 months and the 2 million surviving cells are primary oocytes surrounded by follicular cells. These are now primordial follicles. Atresia continues throughout childhood until the adult state is reached.
Explain the stages that the follicle goes through every months in the time between menarche and menopause.
Pre-antral phase: flat follicular cells become cuboidal and then become stratified (many layers). These are the granulosa cells. A primary follicle occurs.
Antral stage: a fluid filled area, called the antrum, begins to develop between follicular cells. Development of theca interna/externa begins. Only one matures and continues on from here.
