Answer:
The correct answer is b. recognizes foreign DNA sequences that have previously entered the cell and directs the Cas proteins to destroy them.
Explanation:
Clustered regularly interspaced short palindromic repeats (CRISPER) is the sequences of DNA found in the genome of prokaryotes and archaea. These sequences are added at a crisper locus in DNA by bacteria through capturing bacteriophage DNA during infection.
Then this sequence is used to detect a similar sequence of bacteriophage during subsequent infection and destroy them by Cas9 enzyme. Cas 9 enzyme uses a crisper sequence as a template to destroy similar phage DNA.
So the CRISPER Cas system provides an adaptive defense mechanism to bacteria against foreign DNA coming from bacteriophage. Therefore the correct answer is b.
Theoretically it is the Chargaff's rule which entails that the ratio of purines and pyrimidines are 1. So following that rule you can solve this question.
G (purine) = C (pyrimidine) and
A (purine) = T (pyrimidine)
So G + C would be 28% and hence
A +C would be 72% i.e. 36% each.
Please note that their are certain modified bases besides these four are also there including methyl Cytosine, Methylated Adenine. But htese modification does not violate the Chargaff's rule and they follow standard Watson Crick base pairing.
When a Stickleback fish feels threatened, it will flare out its pair of pelvic spines and three dorsal spines, making it difficult for predators to swallow them.
Explanation:
Homologous chromosomes are 2 physically different chromosomes that have the same genes but are not genetically identical. Sister chromatids are 2 copies of a single chromosome and so are genetically identical (they also are physically attached to one another).
