Giardia intestinalis is an intestinal parasite of humans and other mammals that causes intestinal ailments in most people who ingest the cysts. Upon ingestion, each cyst releases two motile cells, called "trophozoites". These attach to the small intestine's lining via a ventral adhesive disk. The trophozoites anaerobically metabolise glucose from the host's intestinal contents to produce ATP. Reproduction is completely asexual, occurring by longitudinal binary fission of trophozoites, with each daughter cell receiving two haploid nuclei (n = 5). A trophozoite will often encyst as it passes into the large intestine by secreting around itself a case that is resistant to cold, heat, and dehydration. Infection usually occurs by drinking untreated water that contains cysts.
-If the mitosomes of Giardia contain no DNA, yet are descendants of what were once free-living organisms, then where are we likely to find the genes that encode their structures, and what accounts for their current location there?
A) plasmids; conjugation
B) plasmids; transformation
C) nucleus; horizontal gene transfer
D) nucleus; S phase

Question

Quizplus · Accepted Answer

Since the mitochondrial structure mitosome does not contain DNA, their genes that encode structures could be found in the nucleus through horizontal gene transfer. Mitosomes are believed to originate from free-living ancestors, which had genes that encoded the structures. Horizontal gene transfer could explain why the genes for mitosomes are now present in the nucleus of Giardia intestinalis.

Giardia Intestinalis Is an Intestinal Parasite of Humans and Other