Section 5.4: Asexual Reproduction

Biology

Types of Reproduction

• Sexual Reproduction• Joining of gametes (sperm and eggs), one

from each parent• Genetically unique offspring

• Asexual Reproduction• Creation of offspring from a single parent• Genetically identical to each other and the

parent organism

Binary Fission

• Way that prokaryotes reproduce

• Asexual reproduction of single-celled organisms

• Very similar to mitosis, with similar results

• Formation of two daughter cells that are identical to the parent cell

Steps of Binary Fission

• DNA is duplicated and chromosomes are attached to the cell membrane

• Bacteria cell grows and elongates

• When cell is approximately twice its normal size it undergoes cytokinesis

• New cell is laid down between the two sets of DNA and two daughter cells are formed

Advantages to Asexual Reproduction

• More efficient

• Decreased genetic variation if cells are suited to the environment they are currently residing in

Disadvantages toAsexual Reproduction

• No genetic variation can be bad if cell is living in an environment that changes routinely• An entire generation or population can die off

• Decreased genetic variation also decreases the likelihood that one or more offspring will survive should conditions change

Asexual Versus SexualReproduction

• Sexual reproduction requires a lot of energy• Attract a mate and all of the behaviors and

signals required for that

• Sexual reproduction also decreases the number of members within the population that can produce offspring

• Asexual reproduction can produce more offspring, quicker, with less cost• But is it really less cost if the diversity is

decreased?

Eukaryotes Reproducing Through Mitosis

• Eukaryotes can reproduce asexually through mitosis

• Common in simple plants and animals

• Three Types:• Budding• Fragmentation• Vegetative Reproduction

Budding

• Small projection grows from parent organism• This will be come a new

individual

• May live independently or as an attached colony

• Example:• Yeast

Fragmentation

• Parent organism splits into pieces which can all grow into new organisms

• Examples:• Sea Stars

• Flatworms

Vegetative Reproduction

• Modification of stem and underground structures of parent organism

• Offspring stay connected to parent organism through structures called runners

• Examples:• Strawberries

• Potatoes

Doing It All

• Some organisms can reproduce both asexually and sexually

• Generally depends upon the current conditions

• Sea Anemone• Binary Fission• Budding• Fragmentation• Sexually with eggs and sperm

Section 5.5: Multicellular Life

Biology

Multicellular Organisms

• Cells need to work together to form larger, more complex structures

• Tissues: groups of cells that work together to perform a similar function

• Organs: groups of tissues that work together to perform a specific function or related functions

• Organ Systems: Organs that carry out similar functions

• All organ systems work together to help the organism maintain homeostasis

Cell Differentiation

• Multicellular life requires that there are many cells performing specific functions• But you start as a fertilized egg, essentially

one cell• How do you get to be whole person?

• Cell differentiation: The process by which unspecialized cells develop into their mature forms and function

Cell Differentiation

• All cells contain all of your DNA

• But only some of that DNA is used

• Certain cell types use specific genes within the DNA, and turn off the rest

• A cell’s location within an embryo determines how it will differentiate• Inner, middle, and outer layers of an embryo

become different tissues and organs

Stem Cells

• Unique type of body cell that have the ability to:• Divide and renew themselves for long periods

of time• Remain undifferentiated in form• Develop into a variety of specialized cell types

• Can divide into:• 2 new stem cells• 1 new stem cell and 1 specialized cell

Stem Cell Classification

• Types of stem cell are categorized according to their potential to develop into different cell types

• Totipotent: Can grow into any cell type• Only fertilized eggs and first few divisions

• Pluripotent: Can grow into any cell type except for totipotent

• Multipotent: Grow into cell type that are of a closely related family

Stem Cell Classification

• May also be classified by their origin

• Adult Stem Cells

• Embryonic Stem Cells

Adult Stem Cells

• Undifferentiated cells located among the specialized cells of many organs and tissues• Also found in umbilical cord blood

• Can be taken from patient, grown in culture, and put back into the patient• No rejection by patient’s immune system

• Few in number, hard to isolate, and tricky to grow

• Can contain DNA abnormalities

• Previously thought that only multipotent• Research has shown that the addition of specific

molecules at the right time might be able to make these cell pluripotent

Embryonic Stem Cells

• Taken from donated embryos left over from in vitro fertilization• Three to five day old embryo

• True pluripotent cells that can turn into any of the 200 different cell types of the body

• Can be rejected by patient’s immune system, or grow a tumor

• Ethical questions surrounding the destruction of the embryo to harvest

Use of Stem Cells

• Used to treat patients with leukemia and lymphoma

• Current research in use of stem cells for diabetes

• Growth of new organs from stem cells, or repair of damaged sections of an organ with specialized stem cells

• Stem cells are also useful when testing new compounds, as the cells can be grown into any tissue, without having that tissue come from or be attached to a currently living human

Review Questions

• Page 150• # 2, 3, and 5

• Page 155• #1-5

• Answer all questions in complete sentences.