Contact:
sales@biotechnologyforums.com to feature here

Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Genes Determine Body Patterns
#1
Every organism has a unique body pattern. Although specialized body structures, such as arms and legs, may be similar in makeup but their shapes and details are different in different organisms. During growth of the embryo, arms and legs develop differently due to the actions of special genes, called homeotic genes.

Homeotic genes are genes that specify how structures develop in different segments of the body. Examples of such genes are Hox and ParaHox genes which are important for segmentation. These genes determining where, when, and how body segments develop in flies. Alterations or mutations in these genes may lead to changes in prototypes of body parts, sometimes causing striking effects such as legs growing in place of antennae or an extra set of wings or, in the case of plants, flowers with abnormal numbers of parts. An individual carrying an altered (mutant) version of a homeotic gene is known as a homeotic mutant.

Organisms can continue to exist and be reproductive even with homeotic gene mutations that produce differences in body shape. This means that homeotic mutations can be an effective means for evolutionary change.
For example, in a mammal, a single homeotic mutation might produce an arm that is shorter, or longer, or broader. Regardless, it will probably still look and work like an arm.

A change in body shape may sometimes lead to its advantage. For example, the mutation may allow it to capture food more effectively or be more attractive in some way. In this case, then the mutant organism may have greater reproductive fitness. And naturally the genes may be passed on to the preceding generations, which may lead to influencing the course of evolution.

These genes were studied in fruit flies having bizarre mutations. They correlated mutations in different genes with transformations in the flies' body patterns.

One example of a homeotic transformation in fruit flies - antenna to leg.
Research led by biologist Ed Lewis, studied fruit flies that had legs growing out of their heads in place of antennae! They found that a mutation in a single gene, called Antennapedia, made this phenotypical change. Scientists believe that this mutation changes not only the antennal structure, but makes that entire segment of the fruit fly's body develop as if it were a different segment.

Dr. Lewis's work depicted that antennal cells carry all of the information necessary to become leg cells. As per the general principle, every cell having its own DNA caries all the information necessary to build the entire organism.

Genes that determine body pattern have common sequence characteristics.
Researchers found while studying the DNA sequences of many genes which controls the body pattern, that each contains a similar stretch of about 180 nucleotides within its sequence. They named this stretch of genes as a homeobox, and classified all genes containing it as homeotic genes. The homeobox is only a portion of each gene. For example, if the words below were homeotic genes, the capital letters would represent the homeobox:
• togeTHEr
• THEoretical
• gaTHEring
• boTHEr

These show the gene expression seen in the fruit fly. Each of the genes in the homeotic complexes is responsible for controlling body pattern in a particular region. It is also noted that the genes in the chromosome are arranged in an order corresponding to the order they appear on the body.
Researchers were curious to know whether organisms other than fruit flies also had homeotic genes that regulated body patterning. It was found that Homeobox sequences found in most mammalian genes are very similar to those in fruit flies. These sequences have been conserved throughout evolution without much change.

Gene sequences sustained over evolutionary time are important to the basic development of even distantly related organisms. For example, flour beetles and fruit flies share a cluster of homeobox genes, called the homeotic complex or HOM-C, that are very similar in sequence and function.

Genes in different organisms that share similar sequence and function are called homologous. The insect HOM-C gene cluster also shares homology with Hox gene complexes in mammals.
Like Post Reply
  

Possibly Related Threads…
Thread
Author
  /  
Last Post



Users browsing this thread:
1 Guest(s)

Genes Determine Body Patterns00