Asexual Reproduction

Is a method of reproduction with all the genetic information coming from one parent.

Some Methods of Asexual Reproduction

1.  binary fission -- involves an equal division of both the organism cytoplasm and nucleus to form two identical organisms -- the diagram of the protist at the right is example of this

2.  budding -- involves one parent dividing its nucleus (genetic material) equally, but cytoplasm unequally -- the diagram of a yeast at the right is an example of this

3.  sporulation (spore formation) -- is reproduction involving specialized single cells coming from one parent -- the diagram of mold spores being formed at

the right is an example of this

• Asexual reproduction is sometimes called cloning.  

• Cloning is the production of identical genetic copies.  

• All forms of asexual reproduction are variations of the cell division process of mitosis.

•Mitosis is associated with asexual reproduction, as well as growth and repair in sexually reproducing organisms.

Mitosis

Mitosis is the method used for cell division and reproduction in cells not involved in sexual reproduction.   

This process starts with one replication (copying of the chromosome material) and one division of the chromosome material.  

This results in the chromosome numbers in the two cells produced being the same as in the parent cell.  

An Overview of the Process of Mitosis

2 Key Results of Mitosis

1. The same chromosome number is retained from generation to generation.2. Each daughter cell receives an exact copy of the chromosomes of the parent cell.  (clones)

Sexual Reproduction

•The process of sexual reproduction involves two parents. •Both parents normally contribute one gamete or sex cell to the process.  • This process assures that the genetic information given to the offspring will be obtained equally from each parent.  •The female gamete is called the egg or the ovum and the male gamete is called a sperm. These gametes are formed in specialized reproductive structures called gonads.   The sperm is much smaller than the egg, but is capable of moving on its own power using

a whip-like tail called a flagellum.

Sperm and Egg(fertilization)

The sperm and egg unite in a process called fertilization.   This process forms a single celled structure called a zygote which contains the complete genetic information to develop into a complete new organism having characteristics of both parents.

Process of Fertilization

This zygote will then divide by mitosis and form the specialized cells, tissues, and organs of the organism.   This development of specialized structures from the zygote is called differentiation.

Meiosis

•The process of meiosis produces gametes or sex cells.   •The process of meiosis halves the chromosome number from the original parent cell in the four cells it forms.   It does this by having two cell divisions forming four cells, where mitosis has only one cell division forming two cells.   •Both processes start out with one doubling or replication of the chromosome material.  

Process of Meiosis

Another important way that meiosis differs from mitosis is the exchange of chromosome pieces which occurs in the first division of this process.   This exchange of chromosome pieces is called crossing over.  

Crossing Over and Genetic Recombination

Development

Initial Development and Differentiation

•The processes of gamete production, fertilization, and development follow an orderly sequence of events.• Zygotes contain all the information necessary for growth, development, and eventual reproduction of the organism. •The zygote, which is a fertilized egg consisting of one cell, will begin to divide rapidly by mitosis forming the early developing human embryo. • Fertilization and the initial stages of this mitotic cell division occur in the oviduct. • The early embryo is migrates down the fallopian tube and completes most of its development in the wall of the uterus.

            Fertilization and Initial Development of the Embryo

•The placenta is a combination of maternal and fetal tissue which allows for the exchange of materials with the fetus and mother.   Needed materials such as food and oxygen diffuse through the placenta to the fetus, while wastes from the fetus diffuse to the mother.   •The umbilical cord is a fetal structure containing blood vessels which allows materials to be carried between the fetus and placenta in both directions.  • The amniotic fluid surrounds the fetus and helps to provide a shock absorber to protect the fetus against mechanical injury in the event the mother is shaken or injured in some manner.

                    Fetal Development in the Uterus

The embryo will eventually develop into a three cell layered structure.   This structure is called a gastrula and will eventually differentiate to form the specialized cells.  Differentiation means that the cells will develop specific jobs and develop into specific tissues in the maturing organism.  

Fetal Development

•Development is a highly regulated process •After this small cluster of cells called the gastrula forms in humans, tissues begin to form. In humans, the embryonic development of essential organs occurs in early stages of pregnancy. • During the first three months of human development, organs begin to form.  The human embryo is usually referred to as a fetus when human like features become visible in its structure.    •All organs and body features are developed by the end of the sixth month.   During the last three months of pregnancy, organs and features develop well enough to function after birth.

 Human Development at 6 weeks Human Development at 4 months

The embryo (or fetus) may encounter risks from faults in its genes and from its mother's exposure to environmental factors such as inadequate diet, use of alcohol,

tobacco, drugs, other toxins, or infections.   .