Genetic code - Principle, Features & Discovery | Biology Blog

                                        Genetic Code

Any biochemical process is ended up by the arbitration of the enzymes. These enzymes are consist of proteins. Every protein is cover of at least 20 amino acids, whereas the DNA is made up of only four nucleotides. The four nitrogenous bases of DNA will tell you all  20 amino acid sequences. All the genetic information for a character is coded in the nucleotide of DNA called  Codon.

The sequence of nucleotide or nitrogenous bases in mRNA molecules which locked the information for protein synthesis and called as Genetic Code.

 Discovery -  In 1968 Nirenberg, Khorana &Holley have discovered genetic code. Nirenberg also received a noble prize for success in genetic code.

  The problem in Genetic code - The major issue of genetic code was to resolve the perfect number of nucleotides in a codon that codes for a single amino acid.

Singlet Code - Since there are only four nitrogenous bases in mRNA ( A, U, G, C ) for 20 amino acids, a combination of only one or two nitrogenous bases can not provide sufficient code words for 20 amino acids. Therefore, the nucleotide to act as genetic codes must act in multiple units. If nucleotide act in units of two possible dinucleotide blending will be 4 * 4 = 16 but these are not sufficient to account for 20 amino acids. e.g.,A,U,G,C .

Doublet Codes - Despite having two nitrogenous bases that form amino acids, the four codons ( AA, AU, AG, AC) are formed which codes only 16 amino acids ( 4 * 4= 16 ).

Triplet Code – In 1954  Gamow told about codon that the three-nucleotide of mRNA together form a codon. It is called Triplet Codon. If the nucleotide is then assumed to be arranged in units of three, the possible trinucleotide blending will be 4 *4*4 =64. These 64 codons are enough for 20 amino acids.

Properties Of Genetic Code -

• Codes or Triplet – A codon of the modern genetic code comprise of three nitrogenous bases of mRNA in specific sequences.
  
  
• Codes are comma-less – There is no comma between the adjacent codons.
  
• Codes are non – overlapping – Codons are non-overlapping, which means the base in the m RNA is not used for different codons.
  
  
• The code is non-ambiguous: Non-ambiguous code means that a particular codon will always code for the same amino acid. In the case of ambiguous code, the same codon could code two or more than two different amino acids.
  
  
• Some codes act as start codons: AUG codon is the start or initiation codon In rare cases, GUG also serves as the initiation codon.
  
  
• Some codes act as stop codons: Three codons UAG, UAA, and UGA are the chain stop or termination codons. They do not code for any of the amino acids. These codons are not read by any tRNA molecules.
  
  
• The code is universal: The same genetic code is said to be present in all the kinds of living organisms including viruses and bacteria.
  
  
• The code has polarity: The code is always read in a fixed direction, i.e., in the 5’→3′ direction. In other words, the codon has a polarity.

Also check- DNA Fingerprinting in Forensic Science 

Mendelian Genetics : Biology Blog

                                    Mendelian Genetics

Genetics is the branch of biology dealing in inheritance and variation of characters generation to generation.         

Gregor Johann Mendel -" The Father Of genetics "was born in 1822 in Heinzendorf, which was a part of Czechoslovakia. He was the inventor of Mendel's law,  a naturalist, a priest who began his genetic experiments on garden pea in 1856 in the garden at the monastery.

Selection of pea plant:  There are some reasons for choosing garden pea (Pisum sativum) for experiments by Mendel like –

1. Pea has many separate contrasting characters.
2. The life span of the pea plant is very short.
3. Flowers show self-pollination.
4. It is easy to artificially cross-pollinate the pea flowers, therefore, the hybrids produced were fertile.

Mendel’s Experiments

• Gregor Johann Mendel - the father of genetics proposed some laws of inheritance.
•          He used garden pea as his sample.
•          Large sampling size gave reliability to his unshakable data.
•          Garden pea plants possessed certain completely opposite traits. Example − tall and dwarf plants

         He worked on the following seven traits of garden pea: 

Working method:

Mendel’s achievement was due to his accurate planning and course of action  –

• He studied only one character at a time.
• He used all available techniques to avoid cross-pollination by undesirable pollen grains.
• He applied mathematics and statistics to analyze the results obtained by him.

Mendel’s Laws of Inheritance

Based on his experiments, Mendel proposed three laws or principles of inheritance:

• Law of Dominance
  
  
• Law of Segregation
  
  
• Law of Independent Assortment

·         Law of Dominance

Recessive alleles will always be hidden by dominant alleles. Therefore, a cross made between a homozygous dominant and a homozygous recessive consequently dominant phenotype expressed.

Law of Segregation

·         When  the two alleles of a pair segregate or separate during gamete formation such that a gamete receives only one of the two factors.

·         In homozygous parents, all gametes produced are similar; while in heterozygous parents, two kinds of gametes are produced in equal proportions.  

 Law of Independent assortment-

·         The law of independent assortment states that when the inheritance of two or more genes occur at one time, their distribution in the gametes and in the progeny of subsequent generations are independent of each other.  To prove this, he did a dihybrid cross. In the dihybrid cross, we consider two characters. (e.g., seed color and seed shape)

·         Yellow color and round shape is dominant over green color and wrinkled shape.

Incomplete Dominance

·         In incomplete dominance, F1 generation has the phenotype that does not resemble either of the two parents but is a mixture of the two.

·         Example − Flower color in dog flower (snapdragon), where:

·         RR − Red flowers

·         rr − White flowers

·         Rr − Pink flowers  

·         Here, the genotypic ratio remains the same as in Mendelian crosses, but phenotypic ratio changes since complete dominance is not shown by R (hence, incomplete dominance).

·         Phenotypic Ratio − 1:2:1 that denotes Red: Pink: White

·         Genotypic Ratio − 1:2:1 that denotes RR: Rr: rr

Multiple Allelism / Codominance:
When a gene exists in more than two allelic forms, it shows the phenomenon of multiple allelism.  A well-known example is the inheritance of A, B, and O blood groups in human beings.  The gene for blood group occurs in three allelic forms  IA, IB and i.  A person carries any two of these alleles.  The gene IA produces glycoprotein (sugar) A and the blood group is A.  The gene IB produces glycoprotein B and the blood group is B.  The gene ‘i’ is unable to produce any glycoprotein and so the person homozygous for it, has O group blood. The genes IA and  IB are dominant over ‘i’.   When IA and  IB are present together, both are equally dominant and produce glycoproteins A and B and the blood group is AB.  They are called codominant alleles.  

Epistasis – Epistasis describes the situation in which a gene masks the genotypic effect of another gene. 

complementary gene

one of two or more genes that when present together produce effects qualitatively distinct from the separate effect of any one of them.  

Supplementary genes

one gene producing a characteristic and the second as only being able to ‘supplement’ this characteristic. 

Polygenic Trait

Polygenic traits are controlled by two or more than two genes (usually by many different genes) at different loci on different  chromosomes. For example, there are two major eye color genes, but at least 14 other genes that play roles in determining a person’s exact eye color.

Pleiotropy - a gene that affects more than one phenotype. Pleiotropic alleles are responsible for  the multiple symptoms of hereditary diseases  such as  cystic fibrosis, sickle cell anemia . 

Lethal gene - a gene that is capable of causing the death of an organism, usually during the development of the embryo. For Example sickle cell anemia disease.

           

 Please Do this worksheet yourself for gaining more confidence  -       

Top 6 Biology Books For 11th

                                   Top  6 Books For Biology 

Hello freinds,     

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Biology Book  Class 11th  

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Top 10 BSc / MSc Biology Books

                              Top 10  BSc & MSc  Biology Books 

Hello friends ,  here I am suggesting you some top books for biology which help you to clear all concepts and ensure you to get success . I am providing you link of books also which you can  purchase on flipkart .

BSc /MSc Biology Book 1 

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What The Doctor Say About Cord Blood Banking

                                  Cord Blood Banking 

 A few years back,    the doctor throws away  the cord  after the delivery of a baby from the  body  of  the mother by means of waste material but now it is known to be a useful source of  blood stem cell . Cord blood is used to treat many genetic and other  disorder of the baby as well as whole family .

The delivering baby contains blood in umbilical cord and placenta .  This blood is rich in  the haematopoietic cell , the cell  can able to turn into any type of blood cell weather it would be red cell ,white cell or platelets .  These  haematopoietic cells are sorted out from the blood of the cord and able to produce blood cell throughout the life of a person .

Now a days every hospital of India ask the future parents for preserving  cord blood  for further use in treating leukemia , genetic disorder ad blood cell -  related diseases of his family .

Setps-

Stem Cell Banking/ Cryoviva Preservation In India

                                        Stem Cell Banking 

All the organism on the earth is produced by a single cell only, the fertilized egg. Eventually,  the cell differentiates or undifferentiated to produce unicellular and multicellular organism respectively. Unicellular organism dies early because there are no possibilities to replace the dead or damaging cell and this is the plus point in a  multicellular organism that all dead, diseased and damaged cell cab be replaced medically.   Research has proved that in human,  it is possible to replace the damaged cell or diseased cell with the help of stem cell treatment.

What is Stem cell -  stem cell is a single hollow cell which has an ability to differentiate further to develop in a  functional organ or tissues of the body ( pluripotent )  like muscle cells, blood cells, etc.  As soon as the time flows multiple of the disease can be treated with the help of stem cells.

Type Of Stem Cell -  There are following type of stem cell used medically -

•                                        Embryonic Stem Cell
•                                        Adult Stem Cell
•                                        Induced Pluripotent   Stem Cell
•                                         Cord Blood Stem Cell 

Embryonic Stem Cell -  This one of the best stem cells comes from a human embryo of under five days of age.  The cell is of pluripotent nature that can be differentiated to turn into any type of cells of the body.   The technique to gain this type of cell is in vitro fertilization i.e.,  a  human embryo could be grown under artificial condition by taking the male and female gamete.

Adult Stem Cell -  Adult stem cells can be taken from either child or adult from a particular organ which further differentiates to develop into a cell of the same tissues or organs.  Like Haematopoietic cells which can able to develop any type of blood cell  - red blood cells, white blood cells, and platelets or plasma cells.
Doctors used the hematopoietic cells or bone marrow cells for a very long time to treat blood-related disorders.

Induced Pluripotent cells -  Doctors are trying to change by means of the artificial method the adult stem cell into the pluripotent cell so that it can function in the same way as the embryonic stem cell does.
If this becomes a success then a person's skin cell can able to transplant to replace the damaging cell. This is the subject of an intern study.

Cord Blood Stem Cell -  After delivery, the blood from the umbilical cord are taken out by the doctor's to get umbilical cord stem cell which is used to treat a various genetic disorder of the family going since a long time.
Although We study more about this topic in my next blog where I will describe the further scope and how it can be done.

Stem Cell Banking - After the recovery of stem cells, the cells are taken out by stem cell banks for further preservation. Here I am describing you step by step that how the stem cell can be preserved  -

1. Firstly, the stem cell is taken out of the body.
2. after that further, their microbiological test or examination is conducted to remove further impurities.
3. If the examination is successful then the cell is mixed with the cry protectant.
4. The final process is to enclosed stem cells into a cryo - bag for future use.
5. For this stem cell bank will charge you some money which you have to deposit yearly. 

What are the Important features of Sycon

                                             Sycon 

Sycon is following the phylum Porifera. They are generally marine in nature and also spongy.   Due to sponginess, they are always attached from the base to the substratum like rocks, glass, coral,  on Mollusc shell. Sycon is generally small just like grain and too soft. Sometimes they are found on the sump . They are also known by many names like pineapple, Q tip sponges, etc. 

Feature -

• They are generally marine animals.
• They are diploblastic in nature.
• The body is covered by two-layer; outer layer is Pinacoderm and the inner one is Choanoderm.
• Sycon having syconoid type of canal system.
• Sponges are radially symmetrical.
• Sponges follow asexual and sexual both types of reproduction.
• Sponges are hermaphrodite .
• Spicules are found on its body surface.
• Sycon does not have any nervous system present on its body, only some neurosensory cells are present.
• the small pore is present on their whole body known as Ostia.
• They respire and excrete through the process of diffusion.  

Also Read- Canal System Of Sycon