Heredity and hereditary changes
- Heredity is the transfer of biological characters from one generation to another via genes.
- Gregor Johann Mendel is pioneer of the modern genetics.
- 1901- reasons behind the sudden changes were understood due to the mutational theory of Hugo de Vries.
- 1902- Walter Sutton observed the paired chromosomes in the cells of grasshopper.
- It was proved that genes are carried via chromosomes.
- 1944 - trio of scientists Oswald Avery, Mclyn McCarty and Colin McLeod proved that except viruses, all living organisms have DNA as genetic material.
- 1961 - Francois Jacob and Jack Monod proposed a model for process of protein synthesis with the help of DNA in bacterial cells.
- It helped to uncover the genetic codes hidden in DNA.
- The science of heredity is useful for
- Diagnosis, treatment and prevention of hereditary disorders
- Production of hybrid varieties of animals and plants
- In industrial processes in which microbes are used.
Transcription :
- With the help of RNA, the genes present in the form of DNA
2. Control the structure and functioning of the body.
- Information about protein synthesis is stored in the DNA.
- Synthesis of appropriate proteins are synthesized by DNA through the RNA. This is called as ‘Central Dogma’.
- mRNA is produced as per the sequence of nucleotides on DNA.
- Only one of the two strands of DNA is used in this process.
- The sequence of nucleotides in mRNA being produced is always complementary to the DNA strand used for synthesis.
- Besides, there is uracil in RNA instead of thymine of DNA. This process of RNA synthesis is called as ‘transcription’.
Triplet codon :
- The mRNA formed in nucleus comes in cytoplasm.
- It brings in the coded message from DNA.
- The message contains the codes for amino acids.
- The code for each amino acid consists of three nucleotides. It is called as ‘triplet codon’.
Dr Har Govind Khorana :
- A scientist of Indian origin.
- Made an important contribution in discovery of triplet codons for 20 amino acids.
- Nobel Prize in 1968.
Translation :
- Each mRNA is made up of thousands of triplet codons.
- As per the message on mRNA, amino acids are supplied by the tRNA.
- For this purpose, tRNA has ‘anticodon’ having complementary sequence to the codon on mRNA. This is called as ‘translation’.
Translocation :
- The amino acids brought in by tRNA are bonded together by peptide bonds with the help of rRNA.
- During this process, the ribosome keeps on moving from one end of mRNA to other end by the distance of one triplet codon. This is called as ‘translocation’.
- Such many chains come together to form complex proteins.
- These proteins control various functions in the body of living organisms and their appearance too.
Mutation :
- Living organisms can produce new individuals like themselves due to genes only.
- Some of those genes are transmitted to the next generation without any changes.
- Due to this, some of the characters of parents are transmitted to their offsprings.
- However, sometimes sudden changes occur in those genes.
- Sometimes, any nucleotide of the gene changes its position that causes a minor change which is nothing but the ‘mutation’.
- Some mutations may be minor but some may be considerable.
- Ex. Mutation may cause the genetic disorders like sickle cell anaemia.