3) Determination

The cells in early mammalian egg are similar in shapes and processes. They are said to be totipotent, which means that all genes of their genome can be potentially expressed. Each of those cells can form a new organism, being separated from other. During farther development egg cells loose totipotention through cell-cells interactions and their developmental fate becomes DETERMINED. Determination must be distinguished from differentiation, because cells can be determined to form the tissue before they are actually differentiated in that tissue.

Molecular mechanisms of gene regulation are also mechanisms of determination. Certain genes can be activated to make the cell determined for current development pathway. Cells in which a set of regulatory

genes have been activated may not actually undergo differentiation

until some time later, when other factors interact

with the regulatory protein and cause it to activate still

other genes.

Its intrinsic, that The commitment of particular cells to certain

developmental fates is fully reversible. This fact allows scientists to create clones.

4) Programmed cell death

Not every cell that is produced during development is destined

to survive. For example, the cells between your fingers

and toes die; if they did not, you would have paddles

rather than digits. Unlike

accidental cell deaths due to injury, these cell deaths are

planned for and indeed required for proper development.

Cells programmed

to die shrivel and shrink in a process called apoptosis.

and their remains are taken up by surrounding cells.

Gene Control of Apoptosis

This sort of developmentally regulated cell suicide occurs

when a “death program” is activated. All animal cells appear

to possess such programs. In the nematode worm, for

example, the same 131 cells always die during development

in a predictable and reproducible pattern of apoptosis.

18 Altering the Genetic Message

In general, the genetic message can be altered in two

broad ways: mutation and recombination.

a) Mutation is a change in base DNA sequence of genes. Some mutations

alter the identity of a particular nucleotide, while

others remove or add nucleotides to a gene.

The cells of eukaryotes contain enormous amounts of DNA, many billions of nucleotides. It's clear that even the most perfect replication system cannot allow cells to avoid replication mistakes. There are different types of mistakes, such as deletion, insertion, base substitution and changes in gene position.

Mutational process is very improtant, because changes in dna sequence create new genes, alleles and chromosomes. Evolution can be viewed as the selection of particular

combinations of alleles from a pool of alternatives. The

rate of evolution is ultimately limited by the rate at which

these alternatives are generated. Genetic change through

mutation and recombination provides the raw material for

evolution. Genetic changes in somatic cells do not pass on to offspring,

and so have less evolutionary consequence than

germ-line change. However, changes in the genes of somatic

cells can have an important immediate impact, particularly

if the gene affects development or is involved with

regulation of cell proliferation.

Mutations are not only a result of replication mistakes, but an impact of aggressive enviroment.

The major sources of physical damage to DNA are

ionizing radiation, which breaks the DNA strands;

ultraviolet radiation, which creates nucleotide crosslinks

whose removal often leads to errors in base

selection; and chemicals that modify DNA bases and

alter their base-pairing behavior. Unrepaired

spontaneous errors in DNA replication occur rarely.

b) Mutation is a change in the content of an organism’s genetic

message, but it is not the only source of genetic diversity.

Diversity is also generated when existing elements of the

genetic message move around within the genome.

A change in the position of a portion of the genetic message is referred

to as recombination. Some recombination events move a

gene to a different chromosome; others alter the location

of only part of a gene.

genetic recombination can occur by two

mechanisms" gene transfer and reciprocal recombination

In gene transfer, one chromosome

or genome donates a segment to another chromosome

or genome.

Reciprocal recombination is when

two chromosomes trade segments. It is

exemplified by the crossing over that

occurs between homologous chromosomes

during meiosis.

Becuse of recombination, bacteria in population can get useful genes from another, viruses are allowed to insert their genome into cell dna. Crossingover allows organisms to produce a huge variety of gametes.

19 Gene Technology

Biotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts.

Biotechnology also utilizes these products for manufacturing purpose.

In medicine, modern biotechnology finds promising applications in such areas as pharmacogenomics

Pharmacogenomics results in the following benefits:

Development of tailor-made medicines. Using pharmacogenomics, pharmaceutical companies can create drugs based on the proteins, enzymes and RNA molecules that are associated with specific genes and diseases. These tailor-made drugs promise not only to maximize therapeutic effects but also to decrease damage to nearby healthy cells.

1) More accurate methods of determining appropriate drug dosages. Knowing a patient’s genetics will enable doctors to determine how well his/ her body can process and metabolize a medicine. This will maximize the value of the medicine and decrease the likelihood of overdose.

2) Improvements in the drug discovery and approval process. The discovery of potential therapies will be made easier using genome targets. Genes have been associated with numerous diseases and disorders. With modern biotechnology, these genes can be used as targets for the development of effective new therapies, which could significantly shorten the drug discovery process.

3) Better vaccines. Safer vaccines can be designed and produced by organisms transformed by means of genetic engineering. These vaccines will elicit the immune response without the attendant risks of infection. They will be inexpensive, stable, easy to store, and capable of being engineered to carry several strains of pathogen at once.

The second branch of industry, where people use biotech., is agriculture. Genetical altering of crops can increase yield, nutritional qualities and reduce vulnerability to enviromental stresses. The process of spoilage can also be slowed down through biotechnology.