Skip to main content

Symmetry


Animals can be categorised on the basis of theirsymmetry. Sponges are mostly asymmetrical,i.e., any plane that passes through the centredoes not divide them into equal halves. Whenany plane passing through the central axis ofthe body divides the organism into two identicalhalves, it is  called radial symmetry.Coelenterates, ctenophores and echinoderms have this kind of body plan Animals like annelids, arthropods, etc., where the body can be divided into identical left and right halves in only one plane, exhibit bilateral symmetry
Labels:

Comments

Post a Comment

Popular posts from this blog

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.
Post a Comment
Read more

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 
9 comments
Read more

Salient Features of Human Genome

Some of the salient observations drawn from human genome project areas follows: (i)The human genome contains 3164.7 million nucleotide bases. (ii)The average gene consists of 3000 bases, but sizes vary greatly, withthe largest known human gene being dystrophin at 2.4 million bases. (iii)The total number of genes is estimated at 30,000–much lower than previous estimates of 80,000 to 1,40,000 genes. Almost all(99.9 per cent) nucleotide bases are exactly the same in all people. (iv)The functions are unknown for over 50 per cent of discovered genes. (v)Less than 2 per cent of the genome codes for proteins. (vi)Repeated sequences make up very large portion of the humangenome. (vii)Repetitive sequences are stretches of DNA sequences that arerepeated many times, sometimes hundred to thousand times. They are thought to have no direct coding functions, but they shed light on chromosome structure, dynamics and evolution. (viii)Chromosome 1 has most genes (2968), and the Y has t...
1 comment
Read more