Cellular Reproduction and Chromosomes

Cancer and Cloning

Cell Clock

• There are only two types of cells that are able to divide continuously– Spermatocytes (sperm producing cells)

• From puberty to old age, spermatocytes are produced• When it eventually becomes a sperm cell and specializes, there

are no more divisions that occur

– Cancer cells• Cancer cells grow so quickly that cell specialization does not

have time to occur. • i.e. Leukemia and white blood cells

Errors in Mitosis

• Mutations are permanent errors in the normal DNA molecule and can severely affect the mitotic process– Mutagens such as toxic compounds, radiation or

viruses can lead to mutations

• Mutations are passed on and only found in the daughter cells of the initially affected cell.

• FHIT gene affected by cigarette smoke will undergo mitosis more frequently then normal and this leads to a tumour

Errors in Mitosis

• Certain genes act like switches and can produce proteins that will turn certain processes like mitosis, on or off.

• A mutation could permanently affect one of these genes and leave a gene switched on permanently– Genes that are activated by a mutation are

called oncogenes and will often lead to tumours

Cancer

• Associated with many diseases but is based around the uncontrolled, unregulated growth of cells.

• After cells in your body specialize, they are only to divide to replace damaged cells.

• There is a balance between cell death and cell replication within the body to keep it healthy!!!

• Cancer disrupts this balance!!!

Cancer• Cells usually don’t divide on their own

– Cancer cells do!• Cancer cells can divide in culture about once every 24 hours. Not in

living organisms though (thankfully!!!)• Cancer cells do not adhere to well to other cancer cells, nor do they

stick well to normal cells.• Metastasis!!!• Cancer cells lack the ability to mature and specialize: Therefore

another threat is that cancer cells cannot carry out some of the functions of normal cells.

Causes of Cancer

• Genetics plays a relatively small role in predicting cancer (breast cancer is one of the few cases where there is documented evidence)

• Lifestyle!!!

Fertilization

• When reproduction occurs there are two ways this can occur:– Asexual Reproduction

• This involves no fertilization, as offspring is produced by a single parent and inherit all the genes and traits from the single parent

– Sexual Reproduction• This involves fertilization of a female egg from

sperm cells of a male producing offspring of many traits.

What is cloning?

• Cloning is the process of forming IDENTICAL offspring from a single cell or tissue.

• For the most part, cloning does not result in the variation of traits that would occur with the combination of male and female sex cells.

• Therefore what kind of reproduction is this?– Asexual

Genetic Engineering

• This discovery has lead to the process of Genetic Engineering!– What is genetic engineering?– The process of intentional production of new

genetic material by substituting or altering existing material.

However it does has it’s problems

– Carrots, ferns, tobacco petunias and lettuce clone well

– But grass and legume families don’t!!!!!– What has been found is that some clones turn

into roots, and others to leaves, which each uses different parts of DNA

– What has resulted in the theory that to clone plant cells well, the process of specialization/ differentiation must be delayed.

Animal Cloning

• During plant cloning experiments, Briggs and King were investigating nuclear transplants

• They extracted the nucleus from an unfertilized egg of a frog using a pipette, making the cell enucleated.

• Next the nucleus of a fertilized cell from the blastula stage and the nucleus was placed into the first cell.

• That cell began to act as a fertilized cell and the cell began to replicate.

• A nucleus that can bring a cell from egg to adult is referred to as totipotent.

Cloning from Adult Animals

• Originally, transferring nuclei from an adult cell (specialized) into an enucleated cell would not stimulate cell division– Why?

• Until recently the only way to clone was to split cells from embryos

• However, some cells would still specialize and full animals could not be cloned

Cloning

• Production of identical copies of molecules, genes, cells or even organisms.

• Ian Wilmut in 1997 = Dolly– Egg from one adult female sheep, removed

nucleus.– Took nucleus from the mammary gland cell of

another sheep and inserted it into the original.– Egg was then implanted into the uterus of a

surrogate mother sheep

Cloning

• Humans?– Any issues?

• Insulin = Gene cloning– Genes that produce insulin are introduced into the DNA of

bacterial cells. Insulin is then manufactured by the bacteria which we can harvest and use for diabetes patients.

• PCR – Polymerase Chain Reaction = Gene Cloning– A single gene, or less, can be copied– Used to amplify or create many copies of DNA

• Useful at crime scenes• Also useful to analyze ancient mummies DNA or in comparison of DNA of

extinct animals to those living today.