Reproduction Flashcards
What are the types of asexual reproduction?
- budding
- parthenogenesis
- regeneration
What is regeneration
- Repair of damage to body
- a form of reproduction in some species
- involves mitosis and differentiation
What is budding?
- similar process to regeneration
- occurs without damage
- may give rise to individuals or colonies
What is parthenogenesis?
- development of egg without fertilisation
- new individual may be haploid or diploid
- invertebrates and few vertebrates
What does sexual reproduction involve?
- Gametogenesis - making sex cells/gametes
- spawning or mating
- fertilisation - getting sex cells to fuse
What is gametogenesis?
• germ cells need to proliferate (
finite time for females, indefinite time for males)
• germ cells need to undergo meiosis in order to exchange genetic material and to half their chromosome complement
What are the different stages of a sperm cell during spermatogenesis?
• spermatogonium divides mitotically
• MEIOSIS - prophase; primary spermatocyte
• after 1st division - primary spermatocyte
• secondary spermatocyte
DIFFERENTIATION
• spermatid
• spermatozoa
What is the site of spermatogenesis?
Seminiferous tubules in the testis
Describe the development of oocyets
- oogonia proliferate through mitosis
- but when they enter into primary oocytes they immediately enter prophase 1 of meiosis
- the primary oocyte stays in this phase until the female animal becomes sexually mature
- second meiotic division only occurs after fertilisation
What is the difference between oogonia and oocytes?
Primordial germ cells migrate to the forming gonad and becomes oogonia.
After a period of mitotic proliferation oogonia differentiate into primary oocytes.
What happens in the first division of meiosis?
In the first division, the homologous chromosomes separate into 2 daughter nuclei.
• cytoplasm divides asymmetrically - one is a small polar body and the other is large cell (containing all developmental potential)
What happens in the second division of meiosis?
Two sister chromatids of each chromosome separate to form 2 haploid cells
• once again, the cytoplasm divides asymmetrically to form another small polar body and the mature ovum.
Summarise gametogenesis in males
- each spermatogonium gives rise to four haploid sperm
- mitosis ceases in the embryo
- meiosis begins at puberty through to end of life
Summarise gametogenesis in females
- each oogonium undergoes mitosis forming primary oocytes
- meiosis begins in the embryo but stays in prophase 1 until puberty
- oocyte remains at metaphase 2 until fertilisation occurs where second division occurs
- otherwise ovulation occurs
What does internal and external fertilisation require?
External - aquatic habitat
Internal - mating
What are the 2 categories of animals with internal fertilisation?
Oviparous - egg bearing
viviparous - live bearing
What is oviparous?
- Egg bearing
* development occurs outside the mother’s body
What is viviparous?
- live bearing
* development occurs inside the mother’s body
What specific organelles does the mother and father provide?
- Sperm provides the centriole
* All of the mitochondria provided by the mother
What is an acrosome?
- cap at the front of the sperm that stores protein
* this is the part that first contacts the egg
What is the zona pellucida?
- the thick outer coating covering the egg
* it is a layer of carbohydrate-covered proteins that surrounds the plasma membrane
What is the function of the zona pellucida?
- protects the egg
* responsible for mediating the initial meeting of the sperm and the egg
Where are cortical granules found and what is their function?
- cortical granules are filled with enzyme and line the inside of the cell membrane
- help make sure that only one sperm can fertilise the egg
What are the differences between the egg and the sperm right before fertilisation?
• sperm has completed meiosis
• egg has not completed meiosis - the chromatids are still attached
- once fertilisation has occurred
• size: sperm is 10,000 times bigger than the sperm
Describe the steps involved in fertilisation
- sperm bind to the zona pellucida
- enzymes of the acrosome are freed and begin to digest the zona pellucida
- sperm tunnels toward the egg’s plasma membrane and 2 membranes fuse allowing sperm to release genetic material into the egg (fertilisation has occurred)
- this triggers a release of calcium ions which cause cortical granules to release their contents and digest the zona pellucida making it unable to bind more sperm
How does the egg cell ensure that only one sperm enters the egg?
- the sperm enters and releases its genetic material into the egg
- sperm activation factors trigger cortical granules to fuse with membrane
- causes a release of calcium ions derived from the egg cell
- cortical granules duse with membrane and enzymes released digest the zona pellucida
- sperm can no longer bind
