Cytogenetics and Cancer Research

The Human Genome Project (HGP) was an international effort and collaborative research program to map and understand the entire human genome. This is a dream project for me to look through of it. I decide to write a review on it in Cytogenetics and Cancer Research blog so that more people can access to this tremendous project.
 

What is human genome?

Human genome is the complete set of DNA (deoxyribonucleic acid) in human body. The DNA contained within each of body cells. The DNA carries the signals to build and maintain the body cells to function so that the heart will keep pumping, brain will keep thinking and bones will keep growing.
 

Overview and History of Human Genome Project

The Human Genome Project was the natural culmination of the history of genetic research. Alfred Sturtevant, an undergraduate student in Thomas Hunt Morgan’s laboratory, found that he could map the locations of fruit fly (Drosophila melanogaster) genes whose mutations the Morgan laboratory was tracking over generations. This is the tremendous start of gene mapping and finally leads to the human genome sequencing project.
 
When the Human Genome Project started in 1990, the researchers had set a goal to complete the project within 15 years but completed it in 2003, with two years to spare. During that time, many volunteers gave blood to provide their DNA as a contribution for the HGP. However, the labels on the blood tubes were intentionally removed to protect the privacy of the donors. Therefore, the final human genome sequence which has been published in 2003 is a combination of many of the donors’ DNA. The researchers had found that 99.9% of everyone’s DNA sequence is exactly the same. However, there are still some tiny fractions of genome that varies among humans. These variations are very important and make all humans unique in physical appearance like colour of eyes and even influence the risk of disease and the response to drugs. Even so, the genome is just one part of the amazing puzzle of human. Lifestyle and environmental factors do influence humans’ health condition too.
 

Contributions of Human Genome Project

By knowing this, the successful of HGP to sequence human genome has made the job of finding genes that cause some genetic diseases easier. The researchers hope that they can find out the genetic basis of other diseases such as heart disease, diabetes and even mental illness so that the drugs and treatments that specifically target these diseases can be designed properly. For example, there are some genes that involved in cancer had already been identified and make the treatment designed much easier.

What have been done in Human Genome Project?

In Human Genome Project, the researchers have deciphered the human genome in three major ways:
 
i. The sequence of all DNA bases in human genome.
 
ii. Maps that show the locations of genes for major sections of human chromosomes.
 
iii. Linkage maps which inherited traits especially those for genetic disease can be tracked over generations.
 
There are about 20,500 human genes revealed in Human Genome Project. This finding appeared to be significantly fewer than previous estimates, which ranged from 50,000 genes to 140,000. This final human genome sequence has given the world a resource of detailed information about the structure, organization and function of the complete set of human genes. This can be considered as the basic set of inheritable information for the development and function of a human being.
 
According to Francis Collins, the director of National Human Genome Research Institute (NHGRI), the genome could be imagine as a book with multiple uses. He said: “It’s a history book – a narrative of the journey of our species through time. It’s a shop manual, with an incredibly detailed blueprint for building every human cell. And it’s a transformative textbook of medicine, with insights that will give health care providers immense new powers to treat, prevent and cure disease.”
 
The Human Genome Project had created many tools that can be used in characterize the genomes of other organisms used extensively in biological research. For examples, mice, fruit flies and flatworms are the model organism that can be used to identify the sequence or function of a homologous (similar) gene in human beings.
 
In conclusion, the Human Genome Project might appear as a perfect project at the first glance. Most probably is the genome was successfully sequenced and the involvement of the government in the project. Yet, the ultimate success of HGP still remains unclear.
 
Reference: National Human Genome Research Institute
 

Is Human Genome Project really beneficial to humans? Leave your precious opinion to start the discussion.

Prader-Willi syndrome or PWS syndrome is thought to be one of the most common genetic disorders. Prader-Willi syndrome and Angelman syndrome were the first examples in humans of genomic imprinting in Cytogenetics. Angelman syndrome has an entirely different clinical condition with PWS syndrome. I will explain about the Angelman syndrome in my future post.
 
What is genomic imprinting? Imprinting is a type of marking process that has a memory. Genomic imprinting is where a segment of DNA is marked or imprinted during gametogenesis. This mark will be retained and recognized throughout the life of the individual. Maternal and paternal inherited alleles will be marked differently and are expressed differently in the offsprings. Therefore, the offspring with the same genetic material will have different appearances. The individual with Prader-Willi syndrome is because the loss of paternally inherited region 15q11 – q13 of chromosome 15. Simple to say, the PWS individual does not inherit the region 15q11 – q13 of chromosome 15 from his/her father but only from mother.

Prader-Willi syndrome is the most common genetic cause of marked obesity in humans according to Cytogenetics. It is a complex disorder with cardinal features of
 
i)    Infantile hypotonia (low muscle tone)
 
ii)   Mild growth retardation
 
iii)  Frequent occurrence of breech presentation (baby enters the birth canal with the buttocks or feet first)
 
iv)  Small hands and feet with gracile and tapering fingers
 
v)   Microcephaly (smaller head)
 
vi)  Almond-shaped eyes
 
vii) Mental deficiency (average IQ of 65)
 
viii) Short stature and so on.
 
From the age of about one and half years onward, hyperphagia becomes a serious problem, leading to gross obesity. Due to hyperphagia and gross obesity, diabetes often sets in during adolescence or later. Epilepsy is found in a minority of cases. Mental development is characterised by moderate to severe retardation with tendency to behaviour disorders, especially reactive to food deprivation. Patients with this syndrome may need specialists for assessment and treatment of their behavioural and learning problems, at the beginning of childhood. Prader-Willi syndrome is present in all races and ethnic groups and most cases are sporadic.
 
In conclusion, Prader-willi syndrome is a genetic disorder that needs treatment and assessment to overcome the learning problem and obesity problem of the patients. I will write a series of Prader-Willi syndrome in this Cytogenetics and Cancer Research blog in order to give people a clear mind about this syndrome. Stay tuned!