question_answer

(i) How does a Mendelian disorder different from a chromosomal disorder?

(ii) Name two chromosomal disorders.

(iii) Give the name of two Mendelian disorders.

Or

(i) How is the ammo acid sequence of a polypeptide chain is related with nucleotide sequence of mRNA?

(ii) Write the characteristics of genetic code.

Answer:

(i) Differences between Mendelian and chromosomal disorders are as follows
Mendelian disorders	Chromosomal disorders
These are due to alteration in a single gene.	These are caused due to absence or excess of one or more chromosomes or abnormal arrangement of one or more chromosomes.
These disorders are transmitted to the next generations through Mendelian principles of inheritance.	These disorders are not transmitted to the next generation as the affected individual is sterile.
These abnormalities develop due to mutations. These may be recessive or dominant in nature.	These abnormalities develop due to defective synapsis and disjunction. These are always dominant in nature.
The defect can be predicted through pedigree analysis.	The defect can be known through amniocentesis.
(ii) Two chromosomal disorders are Turner's syndrome and Down's syndrome.
(iii) Two Mendelian disorders are phenylketonuria and sickle - cell anaemia.
Or
(i) The relationship between the sequence of amino acids in a polypeptide and nucleotide sequence of DNA or mRNA is called genetic code.
(ii) Characteristics of genetic codes are as follows
(a) Triplet code Three adjacent nitrogen bases constitute a codon which specifies the placement of one amino acid in a polypeptide.
(b) Start signal Polypeptide synthesis is signaled by two initiation codons, commonly AUG or methionine codon and rarely GCT or valine codon. They have dual functions.
(c) Stop signal Polypeptide chain termination is signalled by three termination codons, i.e. UAA, UAG and UGA. They do not code for any amino acid and are hence also called non - sense codons.
(d) Universal code The genetic code is applicable universally, i.e. a codon specifies the same amino acid from a virus to a tree or human being.
(e) Unambiguous codons One codon specifies only one amino acid and not any other.
(f) Commaless The genetic code is continuous and does not possess pause after the triplets. tf a nucleotide is deleted or added, the whole genetic code will be read differently.
(g) Non - overlapping code A nitrogen base is specified by only one codon.
(h) Degeneracy of code Since, there are 64 triplet codons and only 20 amino acids, the incorporation of some amino acids must be influenced by more than one codon. Some amino acids are specified by two (e.g., phenylalanine, i.e. UUU, UUC) to six (e.g., arginine, i.e. CGU, CGC, CGA, CGG, AGA, AGG) codons and are called degenerate or redundant codons.