Download lesson-2-explore-page-129-asexual-reproduction

Middle School Science
Room 212 – Miss Lida
Lesson 2 / Explore – Page 129
“Asexual Reproduction”
What is Asexual Reproduction?
 In asexual reproduction, one parent organism produces offspring without meiosis and
fertilization.
 Because the offspring inherit all of their DNA from one parent, they are genetically
identical to each other and to their parent.
Types of Asexual Reproduction
 There are many different types of organisms that reproduce by asexual reproduction.
 In addition to fungi, bacteria, protists, and plants, and animals can reproduce asexually.
Fission
 Cell division in prokaryotes that forms two genetically identical cells is known as fission.
 Fission begins when a prokaryote’s DNA molecule is copied. Each cop-y attaches to the
cell membrane. Then the cell begins to grow longer, pulling the two copies of the DNA
apart. At the same time, the cell membrane begins to pinch inward along the middle of
the cell. Finally the cell splits and forms two new identical offspring. The original cell no
longer exists.
 E.coli, a common bacterium, divides through fission.
 Some bacteria can divide every 20 minutes.
Mitotic Cell Division
 Many unicellular eukaryotes reproduce by mitotic cell division. In this type of asexual
reproduction, an organism forms two offspring through mitosis and cell division.
Budding
 In budding, a new organism grows by mitosis and cell division on the body of its parent.
The bud, or offspring, is genetically identical to its parent. When the bud becomes large
enough, it can break from the parent and live on its own. In some cases, an offspring
remains attached to its parent and starts to form a colony.
 The hydra goes through the process of budding and is an example of a multicellular
organism that can reproduce asexually.
 Unicellular eukaryotes, such as yeast, can also reproduce through budding.
Animal Regeneration
 Another type of asexual reproduction, regeneration, occurs when an offspring grows
from a piece of its parent. The ability to regenerate a new organism varies greatly
among animals.
Producing New Organisms
 Some sea stars have five arms. If separated from the parent sea star, each arm has the
potential to grow into a new organism. To regenerate a new sea star, the arm must
contain a part of the central disk of the parent. If conditions are right, one five-armed
sea star can produce as many as five new organisms.
 Sea urchins, sea cucumbers, sponges, and planarians can also reproduce through
regeneration.
Producing New Parts
 Regeneration of damaged or lost body parts is common in many animals. Newts,
tadpoles, crabs, hydra, and zebra fish are all able to regenerate body parts. Even
humans are able to regenerate some damaged body parts, such as the skin and the liver.
This type of regeneration, however, is not considered asexual reproduction. It does not
produce a new organism.
Vegetative Reproduction
 Plants can also reproduce asexually in a process similar to regeneration. Vegetative
reproduction is a form of asexual reproduction in which offspring grow from a part of a
parent plant.
 Vegetative reproduction usually involves structures such as the roots, the stems, and
the leaves of plants.
 In addition to strawberries, many other plants can reproduce by this method, including
raspberries, potatoes, and geraniums.
Cloning
 Cloning is a type of asexual reproduction performed in a laboratory that produces
identical individuals from a cell or from a cluster of cells taken from a multicellular
organism.
 Framers and scientists often use cloning to make copies of organisms or cells that have
desirable traits, such as large flowers.
Plant Cloning
 Some plants can be cloned using a method called tissue culture. Tissue culture enables
plant growers and scientists to make many copies of a plant with desirable traits, such
as sweet fruit. Also, a greater number of plants can be produced more quickly than by
vegetative reproduction.
 Tissue culture also enables plant growers to reproduce plants that might have become
infected with a disease. To clone such a plant, a scientist can use cells from a part of a
plant where they are rapidly undergoing mitosis and cell division. This part of a plant is
called a meristem. Cells in meristems are disease-free. Therefore, if a plant becomes
infected with a disease, it can be cloned using meristem cells.
Animal Cloning
 In addition to cloning plants, scientists have been able to clone many animals. Because
all of a clone’s chromosomes come from one parent (the donor of the nucleus), the
clone is a genetic copy of its parent. The first mammal cloned was a sheep named Dolly.
 Scientists are currently working to save some endangered species from extinction by
cloning.
 Although cloning is an exciting advancement in science, some people are concerned
about the high cost and the ethics of this technique.
Advantages of Asexual Reproduction
 Asexual reproduction enables organisms to reproduce without a mate.
 Asexual reproduction also enables some organisms to rapidly produce a large number of
offspring. For example, crabgrass reproduces asexually by underground stems called
stolons. This enables one plant to spread and colonize an area in a short period of time.
Disadvantages of Asexual Reproduction
 Asexual reproduction produces offspring that are genetically identical to their parent.
This results in little genetic variation within a population.
 Another disadvantage of asexual reproduction involves genetic changes, called
mutations, that can occur. If an organism has a harmful mutation in its cells, the
mutation will be passed to asexually reproduced offspring. This could affect the
offspring’s ability to survive.