- Slides: 36
Asexual vs Sexual Reproduction
• http: //educationportal. com/academy/lesson/asexual-versussexual-reproduction. html#lesson
Reproduction: The Continuity of Life Reproduction Sexual Reproduction Asexual Reproduction
Question • How might the asexual reproduction of genetically identical plants be useful to humans? • Answer We could theoretically grow a particular plant in abundance • How could it prove harmful to our food supply? • Answer: if condition change a significant portion of our food supply could be adversely affected.
Asexual Reproduction: Identical Offspring • Budding • Regeneration • Parthenogenesis … Cloning? ? ? Genetically
Binary fission is similar in function to mitosis. • Asexual reproduction is the creation of offspring from a single parent. – Binary fission produces two daughter cells genetically identical to the parent cell – Binary fission occurs in prokaryotes. DNA duplicates cell begins to divide daughter cells
Budding… • New Organisms Arise as an Outgrowth from the Parent Organism • Seen Mostly in Marine Animals – Examples Include; Sponges, Corals and Jellyfish… Coral Polyp Photo courtesy Jeffrey N. Jeffords http: //oceanworld. tamu. edu/students/coral 1. htm
Some eukaryotes reproduce through mitosis. • Budding forms a new organism from a small projection growing on the surface of the parent. Hydra bud Yeast
• Yeast cell cycle including budding: • http: //brodylab. eng. uci. edu/cgibin/jpbrody/animation/files/13977277560. html
Can I have some spore? • Spore Formation – spores = small specialized cells that contain a nucleus and cytoplasm surrounded by a thick outside wall which protects the spore. Under the right conditions the spore can rise to a new organism. Found in bacteria, molds, yeast, mushrooms, mosses, ferns and some protozoans.
Regeneration… • This refers to the ability of some animals to re-grow severed parts. • Some of these animals can also grow new organisms from the severed pieces (Segmented Worms and Sea Stars)
VEGETATIVE REPRODUCTION • Fragmentation is the splitting of the parent into pieces that each grow into a new organism. • Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant.
• Bulb = Short underground stem surrounded by thick leaves. Contain stored food. As the plant grows it produces new bulbs which will grow into new plants. Tulips, onions, and lilies.
• Corms = Similar to bulbs but do not contain leaves, just undergroun d stems. Water chestnuts.
• Tuber = enlarged part of an underground stem that contains stored food. Potatoes are tubers. “Eyes” = tiny buds that can form a new potato plant. How you plant potatoes. Great potato famine.
• Runner or stolon = horizontal stem above the ground with buds. If a bud touches the ground it will form roots and stems and start a new plant. Strawberries.
• Rhizome = horizontal stem that grows underground. Thick and contains stored food. Upper portion form nodes which will form buds which will form new plants. Lower portion forms roots. Ferns, cattails, and water lilies.
ARTIFICIAL VEGATATIVE REPRODUCTION Watch out for those old ladies. • Cutting = use a portion of a developed plant to make a new plant. Roses, ivy, and grapevines are reproduced in this way.
• Layering = a stem is bent so that it is covered with soil. Once the branch forms roots it is disconnected from the original plant. • Raspberries and roses.
• Grafting = Bud or stem of one plant is permanently attached to the stem or trunk of a very similar plant. The cambium layers grow together and form a single plant. Apple trees.
Why Bother? ? • Advantages to artificial vegetative propagation: 1. Plants that grow from seed are not always exactly the same as their parents. 2. Takes less time to artificially propagate. 3. Can create seedless fruits. 4. Grafting can be used to generate higher levels of fruit and nut production.
Parthenogenesis… • Offspring can arise from unfertilized eggs. • Includes some Fish, Reptiles, Amphibians and Aphids. • Most of these species can switch between Sexual and Asexual Reproduction. http: //aolsearch. aol. com/aol/image. Details? invo cation. Type=image. Results&query=photos+of+pa rthenogenic+species&img http: //www. duke. edu/%7 Ejsr 6/H awaiipics/Rhampho. jpg (depending on conditions) http: //spot. colorado. edu/~noyesr/TEACHING/480 0%20 Fall%202002. %20 Biology%20 and%20 Evolutio n%20 of%20 Sex/Gynogenesis. Poecilia. pdf www. ag. ndsu. nodak. edu
WHY? ? ? • Why would these organisms prefer asexual reproduction in stable conditions and sexual reproduction in more uncertain or less favorable conditions?
Imagine… • Imagine that a particular organism within a species lacks a certain gene (or ability to express a certain gene) necessary to break down a specific type of food, yet others of the same species within the population are able to break down that food. • What happens if the uncertain or less favorable conditions lead to that being the primary food source?
Death… • The parent organism and all of their offspring produced through parthenogenesis would die! • But, with the genetic diversity that comes from sexual reproduction the possibility of the offspring surviving is enhanced.
• Environment determines what form of reproduction is most advantageous. – Asexual reproduction is an advantage in consistently favorable conditions. – Sexual reproduction is an advantage in changing conditions.
Stem Cells—multicelluar life
Multicellular organisms depend on interactions among different cell types. • Tissues are groups of cells that perform a similar function. • Organs are groups of tissues that perform a specific or related function. stem • Organ systems are groups of organs that carry out similar functions. vascular leaf shoot system SYSTEMS CELL TISSUE ORGAN lateral roots primary root system tissue
Specialized cells perform specific functions. • Cells develop into their mature forms through the process of cell differentiation. • Cells differ because different combinations of genes are expressed. • A cell’s location in an embryo helps determine how it will differentiate. Outer: skin cells Middle: bone cells Inner: intestines
Question • Why is regulation of the differentiation process during the early stages of development so critical? • The early stages lead to the development of progressively more specialized tissues and organs. Distribution of cell differentiation in the early stages could cause severe abnormalities in an organism’s body structure.
Stem cells are unique body cells. • Stem cells have the ability to – divide and renew themselves – remain undifferentiated in form – develop into a variety of specialized cell types
Stem cell video • http: //www. youtube. com/watch? v=t. Pul. EAry. P O 0
• Stem cells are classified into three types. – totipotent, or growing into any other cell type – pluripotent, or growing into any cell type but a totipotent cell – multipotent, or growing into cells of a closely related cell family
• Stem cells come from adults and embryos. – Adult stem cells can be hard to isolate and grow. – The use of adult stem cells may prevent transplant rejection. – The use of embryonic stem cells raises ethical issues – Embryonic stem cells are pluripotent and can be grown indefinitely in culture. First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell mass. These cells are then removed and grown with nutrients. Scientists try to control how the cells specialize by adding or removing certain molecules.
• The use of stem cells offers many currently realized and potential benefits. – Stem cells are used to treat leukemia and lymphoma. – Stem cells may cure disease or replace damaged organs. – Stem cells may revolutionize the drug development process.