Afferent nerve fibers carry signals from the somatic receptors to the posterior horn of the spinal cord or to the brainstem. So i beleive it is 4 but not too sure. Hope this helped a bit (:
Answer: i- fraternal or dyzygotic twins
ii- monozygotic twins
Explanation: dyzygotic twins develop when two separate oocyte are fertilised by two different spermatozoa. They are also referred to as nonidentical or fraternal twins. They can be of the same or different sex.
Monozygotic twins develop when one oocyte fuses with one spermatozoa and splits into two after fertilization. These twins are also known as identical twins as they will be of the same sex and have the same gene, blood groups and physical features. They may be of different sizes and often have very different personalities and characters.
DNA replication occurs in the 5 prime (5') to 3 prime (3') direction.
I'm sure you've heard this many times. I tutor in genetics, and all of my students can rattle that off. Less understand what it means.
First, understanding what 5' and 3' mean is important. DNA is composed of a ribose sugar, a phosphate group, and a base (A,T,G,C). The sugar has a phosphate group attached to its fifth carbon, and a hydroxyl group on its 3rd carbon. Nucleotides (separate components of DNA) are linked by the phosphate group and the hydroxyl group. So, every nucleotide is linked at the phosphate group and the hydroxyl group besides two - the two nucleotides at either end of the strand of DNA. The one that leaves a phosphate group exposed is called the 5' end of DNA, and the one that leaves a hydroxyl group exposed is called the 3' end of DNA.
<span>A problem with many students just memorizing that replication occurs in the 5' to 3' direction is that there are two strands of DNA involved in replication. DNA polymerase (the major enzyme responsible for replication) reads the already existing strand of DNA in the 3' to 5' direction, and creates the new strand of DNA in the 5' to 3' direction (meaning that it adds nucleotides to the 3' end of the new strand).</span>
