Sexual and Asexual Reproduction

Outcomes 2.11 Using examples from living organisms discuss the importance of asexual and sexual reproduction to their growth and survival. 5.1 Contrast the advantages and disadvantages of asexual reproduction with those of sexual reproduction. 5.2 Compare external fertilization with internal fertilization. 5.3 Describe fertilization in the earthworm. 5.4 Compare the amniotic egg of reptiles and birds with the structures which form in the uterus of a pregnant mammal.

Asexual reproduction An organism capable of asexual reproduction is able to produce offspring in the absence of a mate. In asexual reproduction, the offspring is a clone of the parent and therefore results in low genetic variation in the species as a whole.

Asexual Reproduction: Copies And Clones Modes of Asexual Reproduction: Budding – a new individual develops from an outgrowth on the body of an organism Ex. Hydra – a simple multicellular animal related to the jellyfish. When growing conditions are favorable, hydra grow one or more extensions on the sides of their bodies. When they are sufficiently large, the buds detach and begin to live freely as new, genetically identical individuals. Roots or shoots – a plant will send out a new root or shoot that develops into a new plant Ex. Strawberry Fragmentation – all species of fungi are thought to be capable of this. A part of the growing mass of fungi breaks off and continues to grow independently

Advantages and Disadvantages Advantages 1. Large numbers of offspring are reproduced very quickly from only one parent when conditions are favourable.  2. Large colonies can form that can out-complete other organisms for nutrients and water.  3. Large number of organisms mean that species may survive when conditions or the number of predators change.  4. Energy is not required to find a mate 

Advantages and Disadvantages Disadvantages  1. Offspring are genetic clones. A negative mutation can make asexually produced organisms susceptible to disease and can destroy large numbers of offspring.  2. Some methods of asexual reproduction produce offspring that are close together and complete for food and space.  3. Unfavourable conditions such as extreme temperatures can wipe out entire colonies.

Sexual Reproduction: Adding Variety Each parent contributes a copy of half its genetic information. This process of combining genetic information from two individual results in offspring that differ genetically from their parents and from each other Sexual reproduction involves two key processes. The formation of the haploid sex cells or gametes, which contain genetic information from the parents Fertilization where the two sex cells join to produce a zygote – the first cell of a new individual

Advantages and Disadvantages Advantages 1. Sexual reproduction is a process that involves organisms that are of the same kind and results to the formation of gametes. 2. When the gametes fuse together, it can completely mixed and combine all the genetic material of both organisms. 3. The combination of the genes helps the organisms to evolve and adapt in a healthier way in order to produce healthy type of species. 4. The combination of the genes assures that there would be a lesser chance for the newly formed organisms to acquire diseases and other defects while on the formation and developing process.

Advantages and Disadvantages Disadvantages 1. This sexual reproduction process will just be evident if both the gametes of two organisms will be fused together. When gametes of the organism will not be fused, it is an indication that sexual reproduction will not take place. 2. There is only limited number of organisms that are capable of undergoing the gestation process and most are the female species or organisms. 3. Organisms are not guaranteed that right after the mating process they will completely produced new organisms since there is no assurance that both the gametes of the two organisms will fuse completely together during the mating process. 4. Sexual reproduction takes longer than before they are able to produce new organisms, which is called the offspring.

External Fertilization 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. However, shedding eggs and sperm into the water is an uncertain method of fertilization: many of the sperm never locate an egg, and many eggs are never fertilized, even if both types of gametes are shed at the same time and in the same place, as is usually the case. Consequently, animals using external fertilization generally release vast numbers of eggs and sperm at one time.

Internal Fertilization Most land animals, both invertebrate and vertebrate, use internal fertilization. In effect, the sperm cells are provided with the sort of fluid environment that is no longer available to them outside the animals’ bodies. The sperm can remain aquatic, swimming through the film of fluid present on the walls of the female reproductive tract. Once fertilized, the egg is either enclosed in a protective shell and released by the female, or held within the females’ body until the embryonic stages of development have been completed. Internal fertilization requires close physiological and behavioral synchronization of the sexes, which involves extensive hormonal control

Types of Internal Fertilization Oviparous – Lay egg outside of the body Reptiles and Class Aves (birds) and some mammals use what is called an Amniotic Egg. Allows for reproduction and development of the egg away from water Much larger, self contained with a leathery, calcified shell There are four membranes used for nourishment and protection: Amnion – fluid filled sac which cushions and protects the embryo. It also allows for exchanged of CO2 and O2 through the shell Yolk Sac – contains stored food Allantois – Holds wastes produced by embryo Chorion – lines inside of cell and encloses the other three membranes Ovoviviparous – live off of yolk supply, but develops in a pouch on the mother’s back, some snakes develop this way. Viviparous – Development within the womb Placenta – developed to help exchange materials between mother and young Present only during pregnancy from both maternal and fetal tissues Born after a period of time, can be single or multiple

Compare and Contrast Oviparous Viviparous

External vs. Internal Fertilization External – egg cells are laid, male moves over and fertilizes. Frogs and fish have females that lay their eggs in the water, the male swims over and fertilizes, the sperm needs the water to swim to the egg Internal – Sperm put into the body, egg is fertilized inside the body. Does not mean that embryo develops within the body, but fertilization takes place inside.

Earthworm Fertilization One of the most interesting aspects of earthworms is their sexuality. Earthworms are simultaneous hermaphrodites, meaning worms have both male and female reproductive organs. During sexual intercourse among earthworms, both sets of sex organs are used by both worms. If all goes well, the eggs of both of the mates become fertilized. You can imagine this is a highly efficient way of ensuring the survival of the species Earthworms can also reproduce themselves if need be. They can regenerate new segments if they lose a few. Most earthworms are better at regenerating tails than heads, but some can. They don't reproduce asexually, however; only half (and likely the head half) of an earthworm split in two will regenerate into a full worm once again