 Gamete  A sperm or egg cell, containing half the usual number of chromosomes of an organism which is found only in the reproductive organs of an organism.  Fertilization  Part of the process of sexual reproduction in which a male reproductive cell and a female reproductive cell combine to make a new cell that can develop into a new organism.  Zygote  A fertilized egg formed by the union of an egg cell and a sperm cell; a zygote can develop into a mature individual.

 All living things can produce offspring.  Reproduction ensures that future generations will live. Without reproduction, life on Earth could not continue.  There are two main types of sexual reproduction:  Asexual reproduction  Sexual reproduction

 Is completed without a partner; only one parent produces offspring.  In most cases, the offspring are genetically identical to the parent which occurs because the offspring gets DNA only from one parent.

 Organisms with a simple structure or complex structures can reproduce asexually.  Examples; Simple structure – bacteria Complex structure – plants and invertebrates  Vertebrates cannot reproduce asexually (one species of lizard are the exception).

 Binary Fission  This process follows the same steps as cell division.  Examples; Single-celled organisms such as bacteria and protists.

 Budding  In this process, the parent grows a small bud or branch on its own body.  When the bud is large enough to live on its own, it separates from the parent and forms a new individual.  Examples; Aquatic invertebrates such as sponges and jellyfish Some yeast

 Fragmentation  This process occurs when pieces of a parent organism that have broken off can produce a new organism.  It is common among planarians; a group of flatworms that live in ponds and streams.  Examples; Planarian flatworms Some plants Fungi

 Parthenogenesis  In this process, female produce eggs that develop without being fertilized.  It is the only type of asexual reproduction that produces offspring with genetic variation.  Examples; Honeybees (use both sexual reproduction and parthenogenesis)

 Advantages:  Is simpler, more efficient – no need to find mates  One individual can produce large numbers of offspring quickly  Disadvantages:  Little to no genetic variation, so population may not survive environmental changes

 Requires two individuals to come together to exchange DNA and reproduce.  Some organisms such as bacteria do not have true males and females.  There are distinct differences between sexual partners in these organisms.  Example;  Bacteria have donor and receiver cells.  The donor cell contributes DNA to the receiver cell.

 In most animals that produce sexually;  A sperm from a male joins with an egg from a female.  During fertilization, these gametes come together to form a zygote.  The zygote develops into an individual.  The DNA is a combination of the DNA from the parents.  Depending on the species, eggs are fertilized in one of two ways; External fertilization Internal fertilization

 External Fertilization  Most animals that live or reproduce in water fertilize eggs outside of the female’s body.  How it works; Female lays her eggs in the water. The make then releases his sperm nearby. The sperm then swims to the eggs and fertilizes them.  Examples; Fish Amphibians

 Internal Fertilization  The eggs of humans and may other animals are fertilized in the mother’s body.  In some species such as birds and reptiles, fertilized eggs are laid in a nest.

 The offspring of most mammals develop inside the mother’s body after fertilization. The developing animal receives nutrients from the mother’s body as it grows. Even after birth, parents may need to feed, protect and teach their young certain skills before they can survive on their own. In some species, the parent- offspring relationship lasts months or years.

 Self-Fertilization  Organisms with both male and female sexual organs can produce sperm cells that fertilize their own eggs.  Plants that can do this are called self-pollinators. Examples; Tomatoes, peas and sunflowers.  Although fertilization occurs on the same plant, it is not asexual. This is because the zygote receives half of its DNA from the sperm cell and half from the egg cell.

 Conjugation  In this process, the donor cell attaches a special bridge-like structure to a receiver cell.  The bridge connecting two individual cells is called a pilus.  DNA passes through the pilus to the receiver cell where it joins the cell’s own DNA.  This DNA exchange introduces new forms of genes to the receiver’s DNA.  After the exchange is complete, the receiver cell reproduces asexually through binary fission.  Examples; Bacteria and protists species

 Advantages:  Increases genetic variation in offspring which helps a species survive changed in the environment  Disadvantages:  More complex  Takes time, energy, resources to find mates and produce offspring  Fewer offspring

 Many types of organisms can reproduce both sexually and asexually.  The ability to reproduce both ways gives organisms an advantage under many circumstances.  Examples;  Bacteria  Fungi  Many plants