L16: Development of multicellular organisms Flashcards
(43 cards)
What cells are egg & sperm derived from?
Germ cells
What happens to germ-cell formation during Day 6.25 (pre-gastrulation)?
Primordial germ cells is seen in proximal epiblast pre-gastrulation, where germ layers form
What happens to germ-cell formation during Day 7.25 (during gastrulation)?
During gastrulation, the PGC move to the posterior side of the embryo
What happens to germ-cell formation during Day 8.5 (post-gastrulation)?
PGC migrate back to embryo
Why does PGC express a different combination of genes to somatic cells?
Needed for cell migration & adhesion
Define gonads
Glands that produce hormones involved in reproduction
Process of PGC reaching to differentiate into eggs or sperm?
PGC enter hindgut endoderm & migrate via dorsal mesentery to reach the genital ridges
Why does PGC remain in initial location?
Exclude them from process of laying down body plan and selecting the healthiest
How is the migration path of PGC controlled ?
Chemical signals in the environment
Define meiosis
Gametes with half the number of chromosomes are produced, zygote will have correct number of chromosomes
How many rounds of cell division needs to occur in meiosis to produce 4 haploid cell from 2 diploid cell?
2
2 cell divisions of meiosis?
1) Chromosomes replicated before 1st cell divison so number is halfed
2) Prophase: replicated homologous chromosomes pair up to undergo recombination
Define diploid
One set of chromosomes
Define haploid
2 sets of chromosomes
Define oogenesis
Formation of female gametes
Define spermatogenesis
Formation of male gametes
Pre development of primary oocyte
Stages of oogenesis
1) PGC stays in posterior end of embryo
2) Migrate back inside
3) Enter ovaries
4) Primary oocytes developed
When does 1st meiotic divison occur in oogenesis?
Not completed until after the ovulation in the adult
When does 2nd meiotic divison occur in oogenesis?
After fertilisation
What happens during oogensis after the PGC enters the ovary?
1) Oogonia divide within the ovary and divide into primary oocytes
2) They enter meiosis in embryo but arrested in prophase of 1st meiotic division until ovulation of the adult
3) After ovulation, the secondary oocyte is developed
4) 2nd meiotic division is completed after the secondary oocyte undergoes fertilisation
Pre birth
Stages of spermatogenesis
1) PGC goes back into embryo & enter testes
2) Arrest in G1 stage (early stages of mitotic cell cycle)
3) Resume after birth
What happens during spermatogenesis after birth?
1) After birth, stem cells are produced by mitosis
2) In a sexually mature animal, spermtogonial stem cells give rise to differentiating spermatocytes
Hypothesis to explain mammalian fetal ovarian germline death
1) Failure of meiotic recombination
2) Apoptosis (cell death)
Structure of the sperm
Head:
- Acrosome
- Nucleus
Midpiece:
- Centrosome
- Mitochondria
Tail:
- Plasma membrane
- Flagellum
