Researchers have found the cause of vision impairment due to ageing as the accumulation of “epigenetic noise” that disrupts gene expression patterns leading to changes in inherent DNA function

Genetics is an all-time favourite of UPSC. Every year you can find a question in prelims. Try this one from CSP 2020:

 

Q.Consider the following statements:

1. Genetic changes can be introduced in the cells that produce eggs or sperms of a prospective parent
2. A person’s genome can be edited before birth at the early embryonic stage.
3. Human-induced pluripotent stem cells can be injected into the embryo of a pig.

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 and 3 only

(c) 2 only

(d) 1, 2 and 3

What is Epigenetics?

• Epigenetics is the study of how your behaviours and environment can cause changes that affect the way your genes work.
• Unlike genetic changes, epigenetic changes are reversible and do not change your DNA sequence, but they can change how your body reads a DNA sequence.
• Environmental stimuli can cause genes to be turned off or turned on.
• This determines a cell’s specialization (e.g., skin cell, blood cell, hair cell, liver cells, etc.) as a fetus develops into a baby through gene expression (active) or silencing (dormant); and nurture.
• This normal epigenetic control on our genes can get altered during normal ageing, stress and disease conditions.

Cellular regulators

• The functioning of cells and tissues in our body are controlled by thousands of proteins that regulate various cellular functions.
• These proteins are in turn encoded by the respective genes which are a part of our genome or the cellular DNA.
• Any minor or major changes to our inherited DNA (addition or mutation) can result in altered protein production, which in turn leads to defective cellular functions.
• This forms the basis for many heritable genetic disorders affecting mankind.

A trigger for various inactivities

• Apart from DNA or protein sequence level alterations, there are other biochemical changes that influence and dictate if a gene should be active or inactive in a given cell type.
• For example, the gene that encodes for the insulin protein is present in the exact form, in every cell of the body.
• However, it is allowed to express only in the insulin-secreting beta cells of the pancreas and is kept inactive in the rest of the cells of the body.
• This phenomenon is tightly regulated by a combination of regulatory proteins that changes the expressivity of the gene.
• Also, the histone proteins that bind the DNA and help to compactly wrap it inside the chromosomes can undergo chemical modifications such as methylations and acetylations on different lysine amino acids within the protein.
• These modifications both on the DNA and its associated proteins alter the chromosomal conformations and regulate gene expression.
• These changes can either unwind the DNA and allow gene expression or can compact the DNA and render the genes in the region inactive or silent.

Epigenetics and the human eye

• The human (and mammalian) eye is a remarkable organ in the course of evolution which has allowed us to “see” the external world clearly and in colour.
• Earlier forms, such as microbes and plants, reacted to light in other ways (for absorption and use, such as photosynthesis).
• The front part of the human eye (cornea, lens and the vitreous humour gel) is transparent, colourless and helps focus the incoming light into the retina, helping us see colour.
• It is the retina that sends the message to the brain.
• Its main component, called the retinal ganglion cells (RGC) are the ones that help in this process of sending the message in the form of electrical signals, called neurons or nerve cells.
• Thus, RGCs are the ones that convert optics into electronics.

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