Gameteogenesis Flashcards
What is gameteogenesis?
The production of gametes (sex cells), generated by meiosis
What is spermatogenesis?
The process of haploid sperm production by the testis, it is a continuous process, with millions of new sperm created each day
What is Oogenesis?
The process of haploid female oocyte production in the ovary, this is a long process where eggs form in the embryo and do not complete full development until years later
Describe the 5 key steps in forming sperm cells (spermatogenesis)
- Spermatagonial stem cells undergo mitosis to become spermatagonium existing in the seminiferous tube
- Spermatagonium undergo mitosis in order to become primary spermatocytes
- Primary spermatocytes undergo meiosis I in order to become secondary spermatocytes (haploid)
- Secondary spermatocytes undergo meiosis II in order to generate 4 early spermatids (haploid)
- Early spermatids differentiate and elongate into sperm cells. The sertoli cells in the testis provides nutrients
How are the testis organised?
- In the testi tubules, germ cells are undergoing spermatogenesis and are supported by the surrounding somatic cells
- These are called sertoli cells
What are sertolli cells?
Somatic cells that supply key signals to support and nurse the germ cells
Define:
- Oogonium
- Oocyte
- Ovum
oogonium= diploid precursor cell that gives rise to the oocyte
oocyte= haploid
ovum= mature haploid oocyte ready for fertilisation (release from the ovary)
Describe the five key steps in Oogenesis
- Human oogonia divide by mitosis while females are still an embryo, and then halts once reaching prophase I, meiosis I
- Approximately 1 million oocytes are then present at birth but do not develop further at the moment
- At puberty, Follicle stimulating hormone (FSH) causes follicles to mature (one each month). This happens by continuing meiosis and halting at metaphase II.
- If the egg is penetrated by sperm then meiosis II will resume
- Corpus letum then secretes specific hormones to prepare the body for pregnancy
What is similar between male and female gametogenesis?
- Both involve meiosis
- Involve extensive morphological differentiation
- Do not survive for long if fertilisation does not occur
What is different between male and female gametogenesis?
- Spermatogenesis produces 4 equivalent gametes through meiotic divisions
- Oogenesis is asymetrical, only 1 egg is formed together along with 3 polar bodies
- Oogenesis is arrested at one or more stages whereas spermatogenesis is rapid and uninterrupted
Can an embryo be fully maternal or paternal?
No. Because of genomic imprinting (some genes are switched off according to parent of origin), both a male and female pronuclei is needed to produce an embryo
What are the 4 main steps of fertilisation?
- The sperm penetrates follicle cells and the zona pellucida (glycoprotein layer surrounding the egg)
- The sperm binds to the ovum, causing an acrosomal reaction where the enzymes in the head of the sperm are digested
- A cortical reaction takes place where granules inactivate other sperm receptors on the egg’s surface to prevent multiple fertilisation)
- A diploid zygote forms from the union of a haploid sperm and haploid egg cell
How does IVF take place?
Hormonal stimulation results in egg maturation
active sperm are added
early cleavage occurs in vitro
embryos are frozen/implanted
What is the most significant cause of human fertility?
- Defective sperm function
What is ICSI?
- Intracytoplasmic sperm injection
= a specialised form of IVF that is used for the treatment of severe cases of male factor infertility
ICSI involves the injection of a single sperm directly into a mature female egg
