Question

1. Explain why identical twins actually still look different (distinguishable from each other).

2. Explain the mechanism responsible for inactivating one of the X-chromosomes in every female

3. In a nutshell, explain how the central dogma of molecular biology has evolved in recent years?

Please answer each question separately and in paragraph form.

Answer 1

1. Identical twins are developed from splitting of embryo from very early stage of development. Here the genetic composition in twins is identical. However it is not similar. Additionally environment affects each genome differently. Both have random mutation by UV exposure and other environmental conditions. Genes of both individuals react differently in different environment (inside or outside of womb), hence their genes expressed differently. Which is the main reason that identical twins are still different from each other. Additionally epigenetic changes are different in both individuals. Other genetic changes like inactivation, expression of mitochondrial genes and spontaneous mutation are also differ in twins.
2. Female has two copies of X chromosomes. So it is very important to inactivate one set of gene present on one X chromosomes otherwise the genes are over-expressed. The mechanism called inactivation of X leads to regulate gene expression in female. Different epigenetic changes (methylation, ubiqutination and phosphorylation) inactivates a copy of gene. Here if we take an example of methylation, methyl group is added to the gene sequence, specifically at GC rich region hence the gene cannot expressed (cannot transcribed) . Epigenetic changes makes the X chromosomal DNA inactivated. The inactivated region is called as heterochromatin region. It is a dense and dark region.
3. The process of replication, transcription and translation is collectively called as central dogma. In the process of replication, two identical replica of a parental DNA is formed. This newly synthesised DNA under go the process of transcription, mRNA is formed from the DNA strand. This mRNA strand has all the information about which protein is being formed during translation. In the last step the amino acid chain or protein molecule is formed from this mRNA strand. The protein become functional or structural depending upon which gene is coded for which protein. After the discovery of DNA and genetic code, function of DNA become more clear. Replication models developed and how DNA is doubled in each cell is explained thoroughly. In recent years, the transcriptional process become more clear and the role of transcriptional factor in cancer lead to a new dimension in genetics.