All living things are composed of small functional units called cells. A single cell is composed of many organelles, out of which the most prominent one is the nucleus. It occupies around 10% of the total cell volume. This nucleus is covered by a nuclear membrane and comprises many components. The vital components include chromatin, nucleoplasm and nucleolus. Chromatin is a structural complex of proteins and DNA. A small portion of the DNA is what forms the gene.
What is Chromatin?
In the early days, the brightly staining objects that appeared in the cell’s nucleus were referred to as “stuff of hereditary”. These coloured bodies were studied further in the 1980s and 1990s with the help of new technological advancements. This coloured hereditary stuff was linear in appearance and showed different parts. They exist in either less condensed form (euchromatin) or more condensed form (heterochromatin). In either case, the condensed form of a chromatin fibre is termed a chromosome. It plays an important role in inheritance. The chromosomes are paired structures that are present as 23 pairs in humans. All 46 (23 pairs) are unique structures composed of tightly packed DNA and histone proteins.
Chromosomal Abnormalities
Usually, the chromosomal structures are distributed to each daughter cell during cell division in a very precise process. Sometimes, this precise process is also prone to error. An incorrect amount of hereditary material carried by the conceptus distorts and disturbs the normal growth pattern. Instead of the normal two, there can be three particular chromosomes (trisomy) or just one chromosome (monosomy). The abnormalities can also be due to structural imbalances like the deletion, translocation, inversion or duplication of the chromosomal structure. Furthermore, a correct amount and structure do not necessarily ensure that the phenotype will be normal. Inappropriate activation or inactivation of a genome segment can also cause abnormalities.
Examples
- Down’s syndrome – Trisomy of the 21st chromosome
- Edward’s syndrome – Trisomy of the 18th chromosome
- Patau syndrome – Trisomy of the 13th chromosome
- Klinefelter syndrome – Additional X chromosome in males
- Turner syndrome – Completely or partially missing X chromosome in females (Monosomy)
- Cri du chat syndrome – Partial monosomy of the 5th chromosome
These are some examples of chromosomal abnormalities that affect humans. These abnormalities can be confirmed or detected with the help of various genetic advancements. Genetic tests are available for several genetic conditions like Tay-Sachs, Down’s syndrome and sickle cell anaemia.
The Need for Genetic Counselling
Genetic counselling has provided significant benefits to human society. A genetic counsellor will inform the concerned individuals about the nature of the mutant condition that concerns them. If the mutation is inherited in a particular fashion, then the probability of the affected offspring can be calculated. The final decision to take a risk is entirely the responsibility of the individual involved; the counsellor cannot make it. Due to this, hereditary chromosomal disorders in humans can be prevented at a very early stage. Thus genetic counselling is vital for three main purposes:
- Diagnosing genetic conditions
- Determining the amount of genetic risk
- Helps to plan medical treatments
Geneticists usually make a family chart (pedigree chart) to scrutinise the mating and investigate genetic disorders in the lineage. Using family pedigree analysis, a genetic counsellor can provide parents with the necessary information they need to make about the risks of genetic diseases in their offspring. Some refined techniques such as fetoscopy and amniocentesis can provide this information at the early stages of pregnancy. Genetic counsellors will also provide strategies to promote mental health.
