The salient features of double helix structure of DNA are as follows:
- There are two polynucleotide chains in a double stranded DNA.
- The backbone is constituted by sugar phosphate.
- The two strands possess anti-parallel polarity, means one chain has polarity 5’-3’ and the other has 3’-5’.
- The two strands of DNA are joined together by hydrogen bonds between purines and pyrimidines.
- Adenine always pairs with Thymine by two hydrogen bonds and Guanine always pairs with Cytosine by three hydrogen bonds.
- The two chains are coiled around each other where the pitch of the helix is 3.4 nm and distance between two base pairs is 3.4 A° (as in case of B-DNA)
- The backbone of DNA double helix is formed by sugars and phosphates where bases are projecting inwards.
incomplete dominance means that when an individual inherits two different dominant alleles from its parents, both alleles are expressed in the phenotype of the offspring, but the each allele affects the other and modifies the phenotype that would be expected from one of these alleles alone. The classic textbook example is that crossing white and red snapdragons results in pink flowers in the F1 generation.If you cross two pink (heterozygous) ones, though, the alleles can segregate into different gametes and you can expect a 1:2:1 ratio of red:pink:white in the F2 generation.
