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Genetics is the study of heredity which is a biological process where a parent passes certain genes onto their children or offspring. This traditional theory is now being challenged by a new area of study focusing on epigenetics. Epigenetics is rapidly increasing within society today providing people with the opportunity to understand things that previously were not recognised.
Deoxyribonucleic acid, commonly known as DNA, is the genetic material in humans and almost all other organisms. DNA information is collected as a code consisting of four chemical bases: adenine (A), guanine (G), cytosine (C) and thymine (T).
Human DNA consists of 3 billion bases with more than 99 percent being the same in all people (Genetics Home Reference, 2019).
The Genetic Code is the set of regulations by which living cells translate data stored in genetic material (sequences of DNA or RNA) into proteins (sequences of amino acids). This genetic code defines a mapping between trinucleotide sequences called codons and amino acids. Transcription, during which a nucleotide sequence is copied from DNA to RNA, is the first step in decoding genetic messages.
The next step involves joining amino acids together to form a protein. The order in which amino acids are combined determines a proteins shape, characteristics and function. However, cells sometimes make mistakes when copying their genetic information and cause mutations. Mutations can be meaningless or influence how proteins are produced and genes expressed (Genetic Code, 2019).
Protein synthesis is one of the most basic biological procedures by which particular proteins are built by individual cells.
Both DNA (deoxyribonucleic acid) and ribonucleic acid (RNA) are engaged in the process. Transcription is the first process in protein synthesis, as seen in figure…. The data encoded in the DNA is transferred to an RNA molecule during transcription as a template is used as one strand of the DNA double helix. The molecule of RNA is sent to the cytoplasm, which helps bring together all the elements needed for the actual protein synthesis – amino acids, ribosomes, RNAs, etc. The second step of protein synthesis is translation which involves the production of proteins, as seen in figure…. Three different types of RNA molecules are involved in the translation process; messenger RNA, different ribosome RNA and multiple transport RNA. In the cytoplasm the mRNA binds with ribosomes, which are the exact sites of protein synthesis (Protein Synthesis, 2019). A mutation is a shift in DNA sequence, either because of errors when copying the DNA or because of environmental variables such as UV light and cigarette smoke.
Sometimes mutations can take place during DNA replication if there are mistakes which are not adjusted. Certain factors such as smoking, sunlight and radiation are key contributors to mutations due to contact with these environmental aspects. If mutations have a positive influence, then there is an opportunity that they will be inherited. For instance, a mutation in the gene that instructs the formation of a protein called haemoglobin causes the disease sickle cell anaemia. Cancer is one of the most common human genetic diseases caused by mutations. In some instances, defective, cancer-causing genes can occur from birth, increasing a person’s risk of getting cancer (Mutation, 2019). A 2017 research released in the journal Science discovered that two-thirds of cancer mutations in cells account for random errors in DNA, not heredity or environmental variables (Rettner, 2019). Epigenetics is the study of heritable gene expression modifications (active versus inactive genes) that do not involve modifications in the underlying DNA sequence – a phenotype change without genotype change – which in turn impact how cells read the genes.
Epigenetic mechanisms are vital to regulate gene expression and architecture of chromatin in mammalian cells, and not surprisingly they play critical roles in both normal heart and heart disease growth. The three mechanisms include DNA methylation, histone modifications, and noncoding ribonucleic acid regulation. Tobacco smoke is proven to directly affect the epigenetic modifications connected with DNA and histone proteins, along with pressure, alcohol, pollution and drugs. This creates a direct effect on gene expression profiles and is therefore linked with a number of multifactorial illnesses, including asthma and cancer, being predisposed. Epigenetic modifications can be inherited from generation to generation so anything that a person is subjected to during their lifetime could have a detrimental effect on their children and grandchildren’s health, also known as transgenerational inheritance. This is hence why parental smoking was correlated with an enhanced danger of hepatoblastoma and childhood leukaemia in children during the preconception period and pregnancy. This highlights the importance of the preconception period during development and how harmful exposures can affect both the growth and development of the foetus and the postnatal health of the child (‘Epigenetics, smoking and public health’, 2019).
The second case study focused on Monozygotic twins and the effects epigenetics can have on them. Identical twins (also known as monozygotic twins) come from a single egg dividing into two and sharing 100 percent of their genes (Hayasaki, 2019). Traditionally, Monozygotic (MZ) twins are considered genetically identical, so any phenotypic variations within MZ twins are traditionally ascribed to environmental factors. High monozygotic twin discordance levels for prevalent disease indicate the potential for involvement of unexplained environmental or epigenetic variables. Recent genome-wide epigenetic trials in monozygotic disease-discordant twins emphasize this design’s ability to effectively recognize epigenetic modifications connected with complex traits (ncbi, 2019). For example, a recent study was undertaken focusing on monozygotic twins Monica and Erika. Doctors discovered a tumour in Monica’s breast however found no signs of any issues with Erika which was very surprising as they also discovered breast cancer in the twins’ mother. Neither twin tested positive for BRCA gene mutations, which account for most breast cancer cases.
The question is how does one twin get breast cancer and the other twin has not a sign of anything wrong when both of their bodies contain the same roughly 20,000 genes? It can be seen that microscopic variations of identical genes can be expressed differently therefore a person’s health, personality or even appearance can differ. Table A in figure…., demonstrates two representative examples of monozygosity determination using microsatellite markers whilst Table B expressed the quantification of X chromosome difference between twin A and B. Graph C shows the comparison of epigenetic values between the siblings of each 3 and 50 year old twin pair. Overall, the study revealed that the patterns of epigenetic modifications in MZ twin pairs diverge as they become older. Differences in epigenetic patterns could be expressed by the impact of both external and internal factors in genetically identical people. Smoking, physical activity or diet, among others, are external indicators suggested to have a long-term effect on epigenetic changes. MZ twins are an ideal illustration of how genetically identical people can display variations and thus provide a distinctive model for studying the contribution/ role of epigenetic modifications in phenotype development (PNAS, 2019).
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