Reproductive Patterns Sexual vs. Asexual Internal and External Fertilization and development Types of Reproduction There are two main types of reproduction: sexual and asexual. Asexual reproduction: The process by which offspring are formed WITHOUT the FUSION of an egg and sperm. Only ONE individual is involved in the process. There are many different forms such as: BUDDING, BINARY FISSION and FRAGMENTATION. Organisms that reproduce asexually do NOT have a gender or sex organs. For example: There are NOT male and female bacteria….just bacteria. Asexual reproduction has several advantages: 1. SESSILE animals (animals that CANNOT move) can reproduce without finding a mate. 2. Allows the production of MANY offspring in a short period of time because all individuals in a population reproduce. Drawback of asexual reproduction: All of the offspring are CLONES (identical in DNA), so if conditions change and they are no longer well adapted to their environment, there is a good chance that all or most will die. Types of Asexual Reproduction: Budding: occurs when a new individual develops on the SIDE of the parent. The OFFSPRING may stay attached or FALL off to begin an independent life. Types of Asexual Reproduction: -Binary Fission: involves the separation of a parent into TWO or more individuals of approximately the same SIZE. Types of Asexual Reproduction: Fragmentation or Regeneration: the SPLITTING apart of an organism into several pieces. Each piece re-grows (regenerates) the missing parts and develops into a new INDIVIDUAL. Starfish Regeneration Sexual reproduction: The process by which offspring are formed by the fusion of egg and sperm to form a diploid (contains TWO copies of each chromosome) ZYGOTE. FERTILIZATION = fusion of egg and sperm Offspring receive HALF of their DNA from each parent. Offspring are GENETICALLY DIVERSE> This type of reproduction increases the genetic diversity of the species. It is ADVANTAGEOUS in environments that are under constant stress. Drawbacks of sexual reproduction: Have to find a PARTNER Have to wait until sexual MATURITY Not all members of the population REPRODUCE Major Mechanisms of Fertilization: External Fertilization: Eggs are shed into the ENVIRONMENT and fertilized by the male. Occurs in moist habitats where development can occur without the fear of DRYING OUT. The process can occur without CONTACT between the parents. Chemical signals coordinate the process insuring the gametes are not WASTED. Major Mechanisms of Fertilization: Internal Fertilization: Occurs when sperm are deposited in or near the FEMALE reproductive tract and fertilization occurs INSIDE the female body. Requires a more SOPHISTICATED reproductive system and cooperative mating behaviors. Embryo Development Embryos can develop INTERNALLY or EXTERNALLY. Internal development means that the embryos develop INSIDE the body of the mother. In order for internal development to occur, there had to have been INTERNAL fertilization. Animals that follow this development pattern are referred to as having “LIVE YOUNG”. Embryos may also develop externally, or OUTSIDE the body of the mother. External development may happen after either INTERNAL or EXTERNAL fertilization. Embryo Protection Externally produced embryos are protected in several ways: They may be covered with a JELLY LAYER which allows for free gas exchange with the environment and provide the embryo with moisture. LARGE numbers of zygotes are produced to insure that some reach maturity. (100’s, 1,000’s, maybe even millions) Internally produced embryos: May be protected by an egg shell, as in reptiles and birds. Some are LEATHERY and some are HARD. PLACENTAL mammals retain their offspring in a special structure called the uterus. Internally protected zygotes have a HIGHER rate of survival, and therefore, less ZYGOTES are produced.