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Genetics

Learn the toughest concepts covered in biology with step-by-step video tutorials and practice problems by world-class tutors

3. Extensions to Mendelian Inheritance
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Organelle DNA Characteristics

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Hi in this video I'm gonna be talking about Oregon L. D. N. A. So mitochondria and chloroplasts are two organelles and they both contain their own DNA. And so sometimes you'll see these written as in T. D. N. A. And this is for the mitochondria and sometimes you'll see C. P. D. N. A. Written for the chlor A. Class. Now cells are classified based on the number of DNA sources they contain not. They contains. So hetero plas Mc cells contain DNA. In the nucleus and from organ I'll sources like the mido or the chloral homo plasma cells contain only DNA from one source. So it could be from the nucleus. Most likely though it's pro chorionic cells and they instead contain DNA just from their nuclear Oid. Now the endosymbiont theory explains partly why certain organelles like mitochondria and chloroplasts would have their own D. N. A. And so this is um it explains how they evolved. So it's states that mitochondria and chloroplasts were once free living bacteria with their own D. N. A. Their own replication system. They were just pro periodic selves just like living by themselves and eventually they were engulfed. Either they entered or the eukaryotic cells just sort of ate it a little. But either way they somehow got inside a eukaryotic cell and once they were in there they weren't degraded they weren't eaten. They just sort of stayed they stayed around kept evolving. And so today the mitochondria and chloroplasts could never be free living mitochondria don't live without a cell but they do still have remnants of that ability of pro periodic celery bacteria because they have their own D. N. A. And so this is kind of explains how to these two random organelles have D. N. A. In them. Now, mutations in the organ L. D. N. A. Can cause some serious medical defects. So one that you might hear is this long word that is summarized in M. E. R. R. F. And it causes deafness, seizures and other issues. And it's a mutation in the mitochondria in human. So here's an example of the endosymbiont theory. You can see here that here's a set well and here's a bacteria that is being engulfed by the cell. Eventually it just like stays inside and evolves into the mitochondria which is how we know today. And because of this pathway this is why mitochondria and chloroplasts have D. N. A. While other organelles do not now the D. N. A. Typically found in organelles is small and circular which is to be expected because that's very similar to pro carry on D. N. A. Which is where they originally came from. So human mitochondrial D. N. A. Has certain properties. It has a heavy chain which has more guanine nucleotides in it and a light chain which has more side isI nucleotides in it. And it's called heavy and light based on actual weight. And the code on code which if you remember that's the three nucleotides that encode for an amino acid code on code is pretty much universal across all organisms, with the exception of the mitochondria and chloroplasts. So for instance, there's only a few cases of this, it's mostly universal but it's really not entirely. So a G. A. Is three nucleotides. It's a code on and normally codes for our ginny, But in fruit fly or Drosophila Leah Mitochondria, it codes for Syrian instead. So the code our code is not universal in mitochondria quarter plus. It's mostly but not 100%. That's kind of an overview of mitochondria and chloroplast. D. N. A. Let's now turn the page.
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Organelle Inheritance

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Okay because the mitochondria and D. N. A. Have the mitochondria and chloroplasts have D. N. A. That's separate from the nucleus inheritance of the organ L. D. N. A. Is different from the nuclear D. N. A. The nuclear DNA each daughter cell gets half right. It's replicated. Each daughter cell gets half. But mitochondrial and chloroplast instead undergo una parental inheritance. And this is when progeny inherent DNA solely from one parent. So mitochondrial DNA. So my mitochondrial D. N. A. Your mitochondrial DNA comes maternally. So my mitochondrial D. N. A. Is the exact same mitochondrial DNA my mother has and I got none of it from my father and the same goes from all of you. This is D. N. A. That you only get from your mother in the case of mitochondrial DNA and humans. So what it would look like is if you have a mutant female and a wild type female mated mutant female mated with a wild type males all the progeny would be mutant. Because if the mutant is in the mitochondria then it's going to be passed all offspring. Whereas a wild type female and a mutant male again having the mutation in the mitochondria, the progeny are all going to be wild type because you get that D. N. A. Only from one parent. And in the case of humans it's from the mother. Now there is this other term that you need to know about called cytoplasmic segregation. And this is when two organelles a portion themselves or divide themselves into different daughter selves. So for instance if you have two organelles. So two types of mitochondria, one mutant and one normal, then the mutant, all the mutant mitochondria will go into one daughter cell and all the wild type mitochondria will go into a separate daughter cell. And this is actually unusual, right? Because it's not that sells just have one mitochondria. They can have hundreds and sometimes even thousands of mitochondria and chloroplasts. And um they divide themselves completely like by themselves cytoplasmic segregation. So what this results in is uh it's called variation and plants. If you don't know what variation means, it just kind of means multiple colors. I'll show you an example of it a second. And then there's also another example of this that you may read about or hear about. And that's called the pokey diaspora fungi. And the pokey mutants grow slower and they grow slower because of mutation in their mitochondria. And they do some great divisions with them and figure out, you know, that it's being inherited through the mother and their cytoplasmic segregation now because of cytoplasmic segregation, an affected female that maybe has mutant and wild type mitochondria can sometimes produce healthy offspring because the wild type will actually segregate itself into a gamut and then that will go on to produce the offspring that's healthy. But this is very rare, right? Because what I said before is, you know, parental inheritance, that means that if you have a mute, if your mom has a mutation in the mitochondria, that's going to be passed to all offspring. The only case that it doesn't happen is if she has a combination of mutant and while type and then sometimes this wild type mitochondria will go into the gametes and those will be used to produce the offspring. So that's how unaffected female female with mutations in mitochondrial could produce healthy offspring if she has both healthy and mutant a mitochondria. So here's an example of irrigation. And what I mean by the irrigation is you can see there most of this plant is green but there are let me not use the green one to do that. But there are spots here where you can see it's white. Now the reason it's why is because there are mutations in the in the chloroplasts. And this is preventing the proper production of chlorophyll and chlorophyll makes plants green. Now because this is a mutation in the chloroplasts under When a plant is reproducing and it's growing all these cells that undergo cytoplasmic segregation. The healthy chloroplasts go and they create these green parts. Then the mutated chloroplasts sort of you know segregate together into their own daughter cells and will produce these white regions here because the white regions are representative of the mutant chloroplast and the green are the ones representing the non mutant ones. So this is an example of cytoplasmic segregation because this is one organism that has some mutant chloroplasts and some healthy and the healthy ones create the green parts of the plant, and the mutated ones are divided into their own daughter selves, and they create the white parts of the plant. So with that let's not move on.
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