The heart has four chambers and four valves that regulate blood flow.
Anatomy:
Left and right atria
Left and right ventries
Mitral valve
Tricuspid valve
Aortic valve
Pulmonary valve
The rungs of the double helix in DNA are made up of nitrogenous base pairs: Adenine, Thymine, Guanine, and Cytosine. The correct answer is C.
Answer:
A. Natural killer (NK) cells are activated in response to interferons or macrophage and Major histocompatibility complex (MHC) and allows direct apoptosis of virus.
Viruses can invade NK cells by inhibiting MHC from reaching the cell surface. Using stimulating the inhibitory receptors and disrupting the activating receptors, viruses can avoid NK cells. MHC act as a ligand of inhibitory receptor, and when bind with inhibitory receptor allows damage to NK cells.
So, if i would be a virus i will use inhibitory receptors stimulation to avoid NK cells.
B. Bacteria are killed by phagocytic immune cell macrophages by engulfing them.
Bacteria avoid macrophages by escaping from phagosome before the lysosome fuses as lysosomal chemical kill the bacteria and some bacteria prevent acidification of the phagosome.
C. Parasites can avoid macrophages by modulating the host's cell cytoskeleton to block proper phagocytosis.
D. Bacteria can avoid dendritic cells by avoiding lysosomal degradation and prevent antigen presentation on MHC molecules that will modulate the entrance to DCs.
E. B cells are responsible for producing antibodies. Activation of B-cell depends on positive and negative signals transmitted through the B-cell receptor (BCR), so genetic polymorphisms and mutations affects the positive and negative signals. If mutation is done showing negative signal, B cell will not the activate and no antibodies will produce.
An allele is a variation of a gene that can be expressed as a phenotype.
Explanation:
Genes are the specific sequences of DNA that code for a particular protein in organisms. When the fertilization occurs each parent contributes one chromosome which is homologous this means that both will have genes on the particular loci. The alleles of the particular genes will come together to express the trait.
Allele is an entity of gene which determines how the gene will express the particular trait like tall, short, round, wrinkle etc. It can be said that allele determines the phenotypic trait of a particular gene.
