NEET UG Biology Molecular Basis of Inheritance

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Chapter-6. Molecular Basis of Inheritance


DNA :- Deoxy ribonucleic acid is the largest biomolecule which has polynucleotide chains with specific arrangement of nitrogen bases that posses coded information of Cryptogram of a large number of hereditary traits


1. Friedrich Miescher - isolated nucleic acid and named nuclein

2. Zacharis - Found nuclein to be restricted to chromatin

3. Alt man - named nuclein of nucleic acid

4. Fisher - discovered purine and pyrimidine bases

5. Chargoff - found purine and pyrimidine content of DNA to be equal with A = T and G = C ( = equal to )

6. Franklin - found DNA to be helix

7. Watson Crick & Wilkins - Double helical model of DNA

8. Linus Pauling - a Nobel Laurete for unravelling protein structure

Functions of DNA :-

1. Autocatalytic Function :- DNA direct its own biosynthesis at the time of DNA replication

2. HeteroCatalytic Function :- Directing Synthesis of another biochemical is called heterocatalytic function

Ex :- Synthesis of RNA over DNA template

In 1948 Beadle and Tatum proposed one-gene one engyme hypothesis which states that a gene controls metabolic machinery of the organism through synthesis of an enzyme. This laid foundation of biochemical genetics

One - Gene and one Polypeptide hypothesis was proposed by Yanofsky (1965). It states that a structural genes specifies the synthesis of a single polypeptide

Ex :- Haemoglobin is made of two α and two β chains (polypeptides) Two separate genes play vital role in synthesis of two different (α and β ) Chains.

Cistron - In biochemical genetics the term gene is replaced by cistron

Regulatory gene - Which controls the functioning of structural genes

Structural gene - Produces biochemicals required for cellular machinery

Split gene - In this coding, bases are not continuous but are interrupted by non- coding sequences

These are respectively called as exons and introns Functional m - RNA is formed by splicing removal of intron portions and fusion of coding parts / Exon portions

A Few enkaryotic genes are without intorns. They are called exonic genes ( = not split genes) /  Processed genes Ex :- histone genes, interferon genes

House - Keeping genes (or) Constitative genes:- Those genes which are always in action because

their products are always required for cellular activities

Ex :- ATPase, Enzymes of glycolysis

Non -Constitutive genes :- Genes which can be switched on or off as per requierments

Types of Non Constitutive genes :-

(i) Inducible - non - constitutive genes :- Remain repressed but are switched on in the presence of an inducer chemical

Ex :- Lac - operon 

(ii) Repressible - non Constitutive genes :- Remain active till switched off by a chemical

Ex :- Tryptophan operon

Single copy genes :- They are represented only once in the which genome

Repeated genes :-Genes having more than one copy in the same genome are called repeated genes

Ex :- histone genes

Cryptic genes :- Genes which are not expressed during the life cyle of an organism

Overlapping genes :- Reported in φ x 174 Virus Three of its genes (E, B and K) overlap others Transposons / Jumping genes :- DNA seqments Which can pass from one place to another in the genome

Transposons may take strong promoters to new sites or cause reshuffling of gene Segments Which lead to change in gene expression

Ex :- Proto oncogene  Oncogene

Tumour Suppressing genes :- Checks unrestricted cell cycles

DNA finger printing :- Dermatoglyphics : Derma - Skin, glyphein - to carve

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