Animal fertilization

Animals Fertilisation

1. By : Vasquez, Biological Science Animal Fertilization

2. Fertilisation   (for animals) (also known as   conception ,  fecundation ,  syngamy  and  impregnation ) is the fusion of  gametes  to initiate the development of a new individual  organism .  In animals, the process involves the fusion of an  ovum  with a  sperm , which first creates a  zygote  and then leads to the development of an  embryo . Depending on the animal species, the process can occur within the body of the female in  internal fertilization , or outside ( external fertilization ). The cycle of fertilization and development of new individuals is called  sexual reproduction .

3. question of how the sperm and the appropriate egg find each other and the question of how only one sperm gets into the egg and delivers its contents. There are three steps to fertilisation that ensure species-specificity: Chemotaxis Sperm activation/ acrosomal reaction Sperm/egg adhesion

4. Chemo-taxis is the movement of an organism in response to a chemical stimulus .  and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. Example:  ( M ovement of sperm towards the egg during fertilization) and subsequent phases of development. Positive  chemotaxis occurs if the movement is toward a higher concentration of the chemical. N egative  chemotaxis if the movement is in the opposite direction. 

5. Bacterial chemotaxis • Counter-clockwise rotation aligns the flagella into a single rotating bundle, causing the bacterium to swim in a straight line. • Clockwise rotation breaks the flagella bundle apart such that each flagellum points in a different direction, causing the bacterium to tumble in place.

6. question of how the sperm and the appropriate egg find each other and the question of how only one sperm gets into the egg and delivers its contents. There are three steps to fertilisation that ensure species-specificity: Chemotaxis Sperm activation/ acrosomal reaction Sperm/egg adhesion

7. Acrosome reaction During  fertilization , a  sperm  must first fuse with the plasma membrane and then penetrate the female  egg  in order to fertilize it. Fusing to the egg usually causes a little problem, whereas penetrating through the egg's hard shell can present more of a problem to the sperm. Therefore sperm cells go through a process known as the  acrosome reaction  which is the reaction that occurs in the  acrosome  of the sperm as it approaches the egg. The  acrosome  is a cap-like structure over the  anterior  half of the sperm's head.

8. question of how the sperm and the appropriate egg find each other and the question of how only one sperm gets into the egg and delivers its contents. There are three steps to fertilisation that ensure species-specificity: Chemotaxis Sperm activation/ acrosomal reaction Sperm/egg adhesion

9. Sperm/egg adhesion Experiments showed that eggs from a population, remained non-adhesive in a solution chemically similar to ovarian fluid but became adhesive seconds after contact with water. Examination of the ultrastructure of the chorion showed that the morphology changed significantly after contact with water, with nodule-like protuberances attached to connective filaments on the surface present in water-hardened but not non-water hardened eggs. 

10. They are two types of Fertilization: Internal Fertilization External Fertilization

11. External Fertilization External fertilization  is a strategy of  fertilization in which a sperm cell unites with an egg cell in the open, rather than inside specialized organs within the bodies of the parents. External fertilization is limited essentially to animals living in aquatic environments. The flagellated sperm must have fluid in which to swim, and the eggs lack a protective coat or shell (so that sperm can penetrate and fertilize them), and would dry out in the air. Almost all aquatic invertebrates, most fish, and many amphibians use external fertilization.

12. External Fertilization • Outside mother • mainly in water • not accurate (because of the harsh environment) but easy and fast and lots of offspring • more eggs released

13. Internal Fertilization Most land animals, both invertebrate and vertebrate, use internal fertilization. Internal Fertilization . In mammals, reptiles and birds the gametes meet inside of the female's body. This is called internal fertilization . All land dwellers need to fertilize  this way because sperm still prefer swimming to walking . Internal fertilization protects the fertilized egg or embryo from predation and harsh environments, which results in higher survival.

14. Fertilization which takes place inside the female body is called Internal fertilization in animals is done through the following different ways. • Copulation - which involves the insertion of the penis or other  intromittent organ into the vagina (in most mammals) or to the  cloaca  in  monotremes , most reptiles, some birds, the amphibian tailed frog and some fish, the disappeared dinosaurs, as well as in other non-vertebrate animals. • Cloacal kiss - which consists in that the two animals touch their cloacae together in order to transfer the sperm of the male to the female. It is used in most birds and in thetuatara , that don't have an intromittent organ.

15. Via  spermatophore , a sperm-containing cap placed by the male in the female's cloaca . Usually, the sperm is stored in spermathecae on the roof of the cloaca until it is needed at the time of oviposition . It is used by some salamander and newt species, by the  arachnida , some insects and some  mollusks .

16.  the growing egg or offspring must be expelled. There are three general ways of doing this: ovoviparity eggs are retained in the female, but the embryo obtains its nourishment from the egg's yolk viviparous being born alive, as are most mammals, some reptiles, and a few fish (as opposed to being laid as an egg) oviparous egg-laying; depositing eggs that develop and hatch outside the body as a reproductive strategy

17. Internal fertilization is characterized by sperm fertilizing the egg within the female; the three methods include: oviparity (egg laid outside female body) ovoviparity   ( egg held within female ) viviparity (development within female followed by live birth).

18. Insect Insects in different groups, including the  Odonata  ( dragonflies  and  damselflies ) and the  Hymenoptera  ( ants ,  bees , and  wasps ) practise delayed fertilisation Anong the Odonata , females may mate with multiple males, and store sperm until the eggs are laid. The male may hover above the female during egg-laying ( oviposition ) to prevent her from mating with other males and replacing his sperm; in some groups such as the darters, the male continues to grasp the female with his claspers during egg-laying, the pair flying around in tandem. Among social Hymenoptera , honeybee  queens mate only on mating flights, in a short period lasting some days; a queen may mate with eight or more  drones . She then stores the sperm for the rest of her life, perhaps for five years or more.

19. How the sperm penetrate the egg (in animals)

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