2
$\begingroup$

It has now been established (according to the Cambridge A level text book) that

organisms form a symbiotic partnership, typically by one engulfing the other – a process known as endosymbiosis. Dramatic evolutionary changes result. The classic examples, now confirmed by later work, were the suggestions that mitochondria and chloroplasts were originally free-living bacteria (prokaryotes) which invaded the ancestors of modern eukaryotic cells (cells with nuclei).

It also states that

It was also discovered in the 1960s that mitochondria and chloroplasts contain small, circular DNA molecules, also like those found in bacteria

and lastly

The DNA and ribosomes of mitochondria and chloroplasts are still active and responsible for the coding and synthesis of certain vital proteins, but mitochondria and chloroplasts can no longer live independently.

So my question is:

Is this DNA found in the mitochondria and chloroplasts coded for in the host's (animal's or plant's) DNA.

If not are there fully formed mitochondria and/or chloroplasts in all gametes (obviously chloroplasts only in the plant gametes) which were transferred directly from the parent who had them transferred directly from their parent and so on?

If so are all the mitochondria and chloroplasts of one type identical in a organism? Are they almost identicle in families (of organisms not the classifictaion Family)?

$\endgroup$
2
$\begingroup$

Is this DNA found in the mitochondria and chloroplasts coded for in the host's (animal's or plant's) DNA.

No, the DNA contained in these organelles it not a subset of the nuclear genome. However, part of the original genome of the prokaryote has been moved to nuclear DNA. That is why, as you cited, they "can no longer live independently."

If not are there fully formed mitochondria and/or chloroplasts in all gametes (obviously chloroplasts only in the plant gametes) which were transferred directly from the parent who had them transferred directly from their parent and so on?

As the child organism would eventually need these organelles, and they can only be inherited, at least one of the gamete must contain them.

For the chloroplast, the general rule is that only one of the gamete provides it. For example, in gymnosperm it is the male gamete (pollen), in angiosperm, it is the female gamete (ovule). Either it is just not present in the other gamete, or a specific exclusion mechanism makes it mono-parentally inherited.

Mostly the same for the mitochondria, with the caveat that (motile) spermatozoa contain mitochondria for their metabolic functions (energy to move), but these are discarded when forming the zygote, and only the maternal mitochondria are inherited. (In plants, mostly maternal too with exceptions)

This does mean that there is a lineage of organelle on one of the parent's side, up to the most recent common ancestor (approximately, the first individual of the species). In humans, this translates to a presumed Mitochondrial Eve from which all human mitochondrial DNA descends from.

If so are all the mitochondria and chloroplasts of one type identical in a organism? Are they almost identicle in families (of organisms not the classifictaion Family)?

Every mitochondrion of an individual organism comes from the stock of mitochondria of the zygote, through replication. They are thus very similar, except for cell specialization (giving particular morphology to the organelles), and possible mutations. Same for the chloroplast.

Mitochondria (and chloroplasts) are basic components of the eukaryotic cell, providing essential functions which are highly conserved in a species, let alone related individuals.

However, this does not means the DNA of these organelle is the same for every individual : different sequences may give the same protein, or mutation may affect non-coding segment of the genome. This is the basis for genetic genealogy, retracing family lineage though analysis of DNA, including mitochondrial DNA.

$\endgroup$
0
$\begingroup$

No to your first question. Mitochondrial DNA (m[t]DNA) is individual to the host's DNA- it has it's own DNAs in the organelles itself. The same goes for chloroplasts. The mitochondrial DNA is officially linked to the mother's X-chromosomes, and since the sperm's mitochondria is destroyed and only the maternal egg cell is left, the mother's mtDNA is remained to pass down.

Mitochondria grow, reproduce, and replicate mtDNA by their own - this is another proof that they used to be prokaryotes, not to mention their circular DNA, double-membrance structure, etc..

I am not so sure about the third question of their evolutionary relationships between each other, but you probably have to know that chloroplasts created food by fixing carbon dioxide, while mitochondria broke down sugars to release ATP.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.