Types of Sexual Reproduction

Vocabulary Conjugation, hermaphrodite Stamen, filament, anther, pollen Pistil, stigma, style, ovary, petals, petals, sepals, pollination external fertilization, internal fertilization

Conjugation Some organisms that reproduce asexually through binary fission can also reproduce sexually by conjugation. Conjugation occurs when two unicellular organisms transfer or exchange some of their genetic material. Some bacteria and certain Protists like Paramecium Example: bacteria like E.coli one cell copies an extra piece of DNA (called a plasmid) and donates the plasmid copy to another cell  

Autogamy “Auto” means “self” Autogamy means an organism can fertilize itself Hermaphrodites are organisms that produce both male and female sex cells within the same individual. Hermaphrodites occur in plants and some animals that are attached to one location and/or rarely come in contact with other individuals of their species. Eg many aquatic organisms (sponges and barnacles), Earthworms, flowers Although autogamy is similar to asexual reproduction, in that there is no input of genetic diversity from a partner, the recombination of chromosomes from the male and female gametes results in offspring with slightly altered genetic information, which can therefore look phenotypically different from their parents. Most plants and earthworms reproduce by autogamy. It is sometimes possible for hermaphrodites to reproduce with other hermaphrodites. In this case, genetic diversity does increase within the population.

Compare Autogamy to Asexual Reproduction No input of genetic diversity from a partner. But the recombination of chromosomes from the male and female gametes results in slightly genetically different offspring It is possible for hermaphrodites to reproduce with other hermaphrodites. In this case, genetic diversity does increase within the population.

Allogamy Allogamy is the fertilization of an egg from one individual with the sperm of another (cross-fertilization). Occurs in most complex animals and some plants Eg. Conifers such as pine and fir trees have separate male and female cones on the same plant. Poplar trees have separate sexes on separate plants.

Fertilization Fertilization is the process in which the nuclei of the male and female gametes fuse together to produce a single cell called a zygote. Sperm cells have long tails “flagella”. Egg cells are much bigger and lack flagella. What does the presence or absence of flagella say about the cells motility?

Types of Fertilization: External Fertilization gametes meet outside of the parents The female deposits unfertilized eggs and males release sperm over the eggs. Occurs in aquatic or moist environments so gametes don’t dry out. (sperm can only swim in a wet environment) Common in fish and amphibians Both gametes and developing young are vulnerable to environment and predators. Large numbers of eggs produced to ensure enough mature offspring survive. fertilization (the exceptions are aquatic mammals, sharks, and some other special types of fish). External fertilization usually occurs among organisms living in aquatic environments. Land animals generally have specialized organs for internal fertilization.

Advantages of External Fertilization: Results in the production of a large number of offspring Easier to find mates as the gametes released can drift (wind, water etc). More genetic variation

Disadvantages of External Fertilization Environmental hazards such as predators reduce the change of surviving into adulthood. Large amounts of gametes go unfertilised and wasted. Not guaranteed that sperm will come in contact with eggs Greater chance of desiccation (drying out) of gametes/zygotes.

Internal Fertilization Gametes meet inside female’s body Occurs in mammals, reptiles, birds, and some types of fish  Provides more nutrient investment into a single egg Provides a wet environment for the sperm and the egg and protection from other environmental conditions. Eg. Temperature regulation Requires specialized structures to ensure meeting of gametes Parents must care for young during gestation All land dwellers need to fertilize this way because sperm still prefer swimming Need specialized structures. Penis

Advantages: Increase chance gametes meet greater change of successful fertilisation More protection against outside environments and predators, and therefore a higher chance of surviving until birth. More selective of their mates  Less chance of desiccation of gametes

Disadvantages Harder to bring both male and female into intimate contact Limited amount of offspring being produced at any given time.  Parents must care for young through out gestation

Disadvantages of Internal Fertilization Complex courtship and mating behaviours Parents (usually female) must care for the young throughout gestation or until the eggs hatch Specialized structures are required to ensure the meeting of gametes

Disadvantages of External Fertilization Large number of gametes must be produced to ensure mature offspring survive Seasonal due to the delicate nature of the gametes Many zygotes are produced but only a few survive due to predation and environmental conditions

Check your understanding How does the process of fertilization occur? What is needed for fertilization to occur? Describe the different forms of fertilization and give an example of an organism that uses them.

Internal and External Fertilization Name an organism for each method How is internal fertilization an advantage over external? Why do you think organisms that reproduce using external fertilization release a large number of eggs and sperm?