12.3A Reproduction Flashcards
What is the significance of Gametogenesis process?
Gametogenesis is important because it is the process that produces functional gametes (egg and sperm cell) either through meiosis from a diploid cell or mitosis from a haploid cell (plants).
These gametes are important because this allows *geneticaly-varied organisms- (offspring) to be formed.
Gametogenesis
a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes by meiosis
Spermatogenesis
a production of mature sperm (spermatozoa) in the seminiferous tubules of the testes
Phases:
- multiplication
- growth
- maturation
spermatogonia ⟶ primary spermatocyte ⟶ secondary spermatocyte ⟶ spermatid ⟶ spermatozoan
Ooggenesis
is development of mature oocytes (eggs) and can take many years
ooginium ⟶primary oocyte ⟶(stops at prophase I)⟶ secondary oocyte (after puberty) ⟶ secondary oocyte (one a month) ⟶ ovum (after ovulation)
Spermatogenesis
Process:
- occurs entirely in TESTES
- EQUAL division of cells
- is involved in gamete production
Gametes:
- 4 gametes produced
- sperm SMALLER than spermatocytes
Timing:
- UNINTERRUPED process
- begins at PUBERTY
- CONTINUOUS
- LIFE-LONG (but reduces with age)
Oogenesis
Process:
- occurs mostly in OVARIES
- UNEQUAL division of cytoplasm
- is NOT involved in gamete production
Gametes:
- 1 gamete produced (and 2-3 polar bodies)
- ova LARGER than oocytes
Timing:
- in ARRESTED stages
- begins in foetus (PRE-NATAL)
- MOTHLY from puberty (menstrual cycle)
- terminates with MENOPAUSE
In Vitro Fertilization (IVF)
is the process of fertilization by extracting eggs, retrieving a sperm sample, and then manually combining an egg and sperm in a laboratory dish. The embryo(s) is then transferred to the uterus.
Intracytoplasmic sperm injection (ICSI)
sperm are injected directly into an egg in a type of IVF
Why is IVF used?
- Blocked or damaged fallopian tubes
- Male factor infertility including decreased sperm count or **sperm motility*
- Women with ovulation disorders, premature ovarian failure, uterine fibroids
- Women who have had their fallopian tubes removed
- Individuals with a genetic disorder
- Unexplained infertility
- Bacterial infection
IVF step by step
1) Testing & Ovarian stimulation:
- hormone (FSH) injection to stimulate egg production
- examine ovaries via transvaginal ultrasound
- blood test for hormone levels (oestrogen & progresterone)
2) Egg retrieval:
- by using utrasound & hollow needle
3) Sperm sample retrieval
4) Fertilization:
- insemination: mixing in a lab dish
- OR ICSI: a single sperm is injected directly into the egg
5) Embryo transfer:
- after 3-5 days embryos are transferred into the uterus via catheter or small tube
6) Pregnancy test
extracting eggs ⟶ retrieving a sperm ⟶ combining them ⟶ embryo transfer
Arguments FOR IVF
- otherwise childless couples able to have a child
- allows people surviving cancer treatmentsto have children later, using gametes harvested prior to radiation or chemotherapy treatments.
- screening and selection of embryos allows to avoid an inherited diseases
- offspring produced by IVF are much longed-for children who are more certain to be loved and cared for
- IVF as a treat to a medical problem of infertility
Arguments AGAINST IVF
- spread of infertility due to inherited defects or diseases
- destruction of excess embryo, potential human lives
- descrimination: selection of embryo(s) to live discarding others
- multiple pregnancies (increased risk to the mother’s health, premature birth and babies with cerebral palsy.)
- increase of older parents as they choose to delay having a family
- There is an excess of unwanted children, cared for in orphanages or in foster homes. These children may have benefited from adoption by couples, children or otherwise, keen to be caring ‘parents‘.
