Chromosomal theory of inheritance

Following this synthesis of ideas, experimental verification of the chromosomal theory of inheritance by Thomas Hunt Morganand his colleagues, led to discovering the basis for the variationthat sexual reproduction produced. Morgan worked with the tiny fruit files,Drosophila melanogaster which werefound very suitable for such studies. They could be grown onsimple synthetic medium in the laboratory. They complete their lifecycle in about two weeks, and a single mating could produce a largenumber of progeny flies. Also, there was a clear differentiation of thesexes – the male and female flies are easily distinguisable. Also, it has many types of hereditary variations that can be seen with low power microscopes.

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Phyllotaxy

Phyllotaxy is the pattern of arrangement of leaves on the stem or branch. This is usually of three types – alternate, opposite and whorled . In alternate type of phyllotaxy, a single leaf arises at each node in alternate manner, as in china rose, mustard and sun flower plants. In opposite type, a pair of leaves arise at each node and lie opposite to each other as in Calotropis and guava plants. If more than two leaves arise at a node and form a whorl, it is called whorled, as in Alstonia.

Emasculation and Bagging

If the female flower is bisexual , removal of anthers from the flower bud before the anther dehisce using a pair of forceps this is called emasculation . Emasculated flowers have to be covered with a bag of suitable size made of butter paper to prevent contamination of its stigma with unwanted pollen . this process is called bagging

The salient features of genetic code

The salient features of genetic code (i)The codon is triplet. 61 codons code for amino acids and 3 codons donot code for any amino acids, hence they function as stop codons. (ii)One codon codes for only one amino acid, hence, it is unambiguous and specific (iii)Some amino acids are coded by more than one codon, hencethe code is. degenerate (iv)The codon is read in mRNA in a contiguous fashion. There areno punctuations. (v)The code is nearly universal:for example, from bacteria to human UUU would code for Phenylalanine (phe). Some exceptions to thisrule have been found in mitochondrial codons, and in someprotozoans. (vi)AUG has dual functions. It codes for Methionine (met) , and it also act as initiator codon

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