Answer:
Watson and Crick proposed the double helical model of DNA.
Explanation:
- This model says that DNA exist as double helix. It has two polynucelotide strands running in opposite direction i.e the strands are anti-parallel.
- Each polynucleotide strand is made up of several nucleotide liknked together by phophodiester bonds.
- The two strands are not coiled upon each other but the double strand is coiled upon itself around a common axis like the spiral stair case. Here base pairs forms the stairs and backbone of two strands form railing. Back bone contains sugar and phosphate.
- The base pairing is specific, adenine always pairs with thymine and guanine always pairs with cytosine. Thus if we see any base pair, it consists of one purine and one pyrimidine.
- The two strands of DNA thus show complementary base pairing.
- The strands are held together because of hydrogen bonding between the bases in opposite strand.
- One full helical turn involves ten base pairs and the base pairs are stacked 3.4 A apart.
- This form is called as B-form of DNA.
A salmon can live out of water for 2 hours
In Spirogyra and allied forms the chloroplast<span> grows as the cell grows, and only divides when this divides.</span><span>
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Answer;
Two recessive alleles are the number of alleles that a person must have to have albinism.
Explanation;
When a trait is recessive, such as albinism, an individual must have two copies of a recessive allele to express that particular trait. Recessive alleles are denoted by a lowercase letter , such as b versus B. Only individuals with a bb genotye will express a recessive trait, hence, the offspring must receive one recessive trait from each parent to exhibit the recessive trait.
