There is external and internal so I'll list th external. The most important is skin then mucus, sweat or secretion, hair, nails and tears which are all part of the integumentary. Some internal defenses are white blood cells and T cells.
The correct answer is Deletion.
DiGeorge syndrome, more commonly considered as 22q11.2 deletion syndrome. It refers to an ailment resulting when a small segment of chromosome 22 is missing. This deletion leads to poor development of many systems of the body.
The medical issues generally associated with 22q11.2 deletion syndrome involve poor immune system function, heart defects, a cleft palate, delayed development with emotional and behavioral issues, and issues associated with diminished levels of calcium in the blood.
<span>The total number of genes present in a population is called the gene pool. Hope this helps </span>