Reproduction and development Flashcards
Parthenogenesis
an example of asexual reproduction in which an egg develops without being fertilised.
In the case of honeybees, males (drones) are fertile haploid adults that arise by parthenogenesis.
In contrast, female honeybees, including both the sterile workers and the fertile queens, are diploid adults that develop from fertilised eggs.
Protandrous
males early in dev, females later
e.g. clownfish
Protogynous
females when smaller, males when larger, can switch
e.g. Wrasse (fish)
hermaphrodites
have both male and female sex organs
Long day breeder
mating, laying egg and incubation = summer
growth of offspring = summer
Short day breeder
mating, pregnancy, delivery = spread across winter
growth of offspring = summer
Asexuality switching
- seasons
- environment
- ratio of males to females etc.
e.g. Daphnia reproduce asexually when environmental conditions are favourable and sexually during times of environmental stress.
sexual reproduction
- the fusion of haploid gametes forms a diploid cell, the zygote.
- The animal that develops from a zygote can in turn give rise to gametes by meiosis.
- The female gamete, the egg, is large and nonmotile, whereas the male gamete, the sperm, is generally much smaller and motile.
- Usually results in only one offspring
Asexual reproduction
new individuals are generated without the fusion of egg and sperm.
For most asexual animals, reproduction relies entirely on mitotic cell division, e.g., parthenogenesis.
AsR works best when the environment is stable.
More offspring are produced. (than one)
Pheromones
chemicals released by one organism that can influence the physiology and behaviour of other individuals of the same species
Fertilisation
Internal
- occurs inside the female
- development occurs inside the body
External
- A moist habitat is almost always required for external fertilisation to prevent the gametes from drying out and to allow the sperm to swim to the eggs
- development occurs outside the body
+ and - of Asexual and Sexual Reproduction
diagram ^^
marsupials and monotremes
Marsupials e.g. kangaroo - are internally fertilised but then premature embryo is born
Monotremes = echidnas have eggs that are internally fertilised and they lay
- fun fact monotremes don’t have nipples they suck milk from chest hairs
Sperm production pathway
seminiferous tubules are part of testes that produces sperm
sperm pass into the coiled duct of an epididymis.
Spermatogenesis produces 4 haploid sperm from one primordial germ cell
Oogenesis
- the development of mature oocytes (eggs)
- a prolonged process in the human female. Immature eggs form in the ovary of the female embryo but do not complete their development until years, and often decades, later.
- oogenesis produces only one functional ovum from an oogonium
- cytokinesis is unequal and almost all cytoplasm goes into one egg (three polar bodies - degenerate)
Female Reproductive System
- gonads = ovaries
- outer layer of ovary = fossicle
- each fossicle consists of an oocyte, a partially developed egg, surrounded by support cells.
- An oviduct, or uterine tube, extends from the uterus towards a funnel-like opening at each ovary.
- Upon ovulation, cilia on the epithelial lining of the oviduct help collect the egg by drawing fluid from the body cavity into the oviduct.
- Together with wavelike contractions of the oviduct, the cilia convey the egg down the duct to the uterus.
- The inner lining of the uterus, the endometrium, is richly supplied with blood vessels.
- The neck of the uterus, called the cervix, opens into the vagina.
Three sets of accessory glands
- seminal vesicles,
- prostate gland,
- bulbourethral glands
Produce secretions that combine with sperm to form semen, the fluid that is ejaculated
Male Reproductive System
- Testes (singular, testis), produce sperm in seminiferous tubules.
- In humans and many other mammals, testis temperature is maintained about 2°C below the core body temperature by the scrotum.
- From the seminiferous tubules of a testis, the sperm pass into the coiled duct of an epididymis.
- During ejaculation, the sperm are propelled from each epididymis through a muscular duct, the vas deferens.
- The ejaculatory ducts open into the urethra, the outlet tube for both the excretory system and the reproductive system.
Sex hormones
- hypothalamus secretes gonadotropinreleasing hormone (GnRH).
- This hormone directs the anterior pituitary to secrete the gonadotropins follicle-stimulating hormone (FSH) and luteinising hormone (LH)
Steroid Sex hormones
- androgens produce testosterone;
- oestrogens produce oestradiol and
progesterone
Ovarian cycle
The FSH, LH and oestrogen levels peak just before ovulation and progesterone will peak post oestrous. Levels will fall if pregnancy does not occur.
After ovulation, the oestradiol and progesterone secreted by the corpus luteum stimulate maintenance and further development of the uterine lining.
The follicular phase of the ovarian cycle is coordinated with the proliferative phase of the uterine cycle.
Pregnancy process
- The zygote begins a series of cell divisions called cleavage
- about 24 hours after fertilisation and after an additional 4 days produces a blastocyst, a sphere of cells surrounding a central cavity.
- A few days later, the embryo implants into the endometrium of the uterus.
- The condition of carrying one or more embryos in the uterus is called pregnancy, or gestation.
Fertilisation process
- sperm makes contact with egg
- Acrosome releases enzymes which break down the protective membrane
- plasma membrane of sperm and egg fuse
- sperm nucleus enters eggs
- Cortical granules fuse with egg plasma membrane which renders the vitelline layer impenetrable to more sperm.
Trophoblast
The outer layer of the blastocyst, the trophoblast, grows outwards and mingles with the endometrium, eventually helping form the placenta
