I have two questions really if you don’t mind.
[QUOTE=solkoe]
I have two questions really if you don’t mind.
In fruit flies, eggs are filled with lots of maternal mRNAs. These mRNAs can be translated into protein without the need for gene transcription. Whether this occurs in human embryos, I haven’t the foggiest idea. Good question though, I am curious as to what the answer is.
[QUOTE=solkoe]
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A haploid cell has a full complement of genes. It has one full set of chromosomes, which contain all the genes necessary for life. (That is, if the sex chromosome included is an X; the Y is incomplete. Similar considerations may apply for other sex determination systems.) Most body cells are diploid, which means they have a double set of chromosomes, and two copies of each gene. One copy is redundant, which can be valuable in case one happens to be a detrimental recessive.
There are many fully functional organisms that are haploid. One example are drones (male bees), which are hatched from unfertilized eggs and have only a single set of chromosomes. The same is true of other males of the order Hymenoptera (bees, wasps, and ants).
Most fungi and some algae and higher plants are also haploid for much of their life cycles.
Regarding cells without nuclei, mammalian red blood cells lack them. Human red blood cells have a life span of about four months.
[QUOTE=Colibri]
Regarding cells without nuclei, mammalian red blood cells lack them. Human red blood cells have a life span of about four months.
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Well, you beat me to it, but I might as well add something. Human red blood cells (erythrocytes) don’t have any nuclei once they reach maturity; but they do have one while still developing from a stem cell in your bone marrow. Here’s a picture of one still with a nucleus. In normal development the red blood cell will eventually purge it though, because it’s not needed to carry and transport oxygen (as well as the other blood gasses).
I understand that haploid cells have one of each gene but some of these genes will be recessive and therefore will not produce functional proteins. That means the cell will die, right?
By the way, what percentage of our genes are recessive?
But red blood cells do contain DNA do they not? Is it that they do not contain a nucleus or that they do not contain a nuclear membrane?
[QUOTE=solkoe]
I understand that haploid cells have one of each gene but some of these genes will be recessive and therefore will not produce functional proteins. That means the cell will die, right?
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Recessive doesn’t mean that gene doesn’t code for a functional protein, it simply means that the protein coded for has its effects swamped by any present dominant gene. Sometimes that is due to no functional protein being encoded, usually it’s purely relative. People with sickle cell still manufacture haemoglobin, it’s just a different form of haemoglobin.
In additon in the vast majority of cases where no protein is encoded the effect is entirely neutral. People with attached earlobes may lack a very specific protein, but the effect of that loss is totally neutral over the entire lifespan.
Added to that the vast majority of proteins are of no use whatsoever to a single cell. Proteins related to toenail structure or tooth size don’t matter one bit to a single cell so it doesn’t matter whether they are recessive or dominant or missing altogether.
Only mitochondrial DNA in mammals.
They dont conatin a nucleus.
The confusion Solkoe exhibited may lie in the fact that most deleterious genes are recessive, since a deleterious dominant is much more rapidly selected against, while a deleterious recessive may be masked for several generations before it happens to match with another recessive and become expressed. However, the converse is not true: most recessive genes are not deleterious. And, of course, whether deleterious or not,they generally code for something – just not what might be useful that their dominant counterpart will.
I’m way outside any of my areas of expertise in this next, but IIRC, what the infant girl has at birth is not a full complement of ova per se, but a full complement of the diploid cells (called something like megaloocytes, IIRC) that will each divide into one ovum and three polar bodies (with the rarissima exception of “polar twins”).
The crux of the question is if protiens necesary for the survival of a cell are synthesized within the nucleous. I would guess not, but I am outside my field.
[QUOTE=solkoe]
I have two questions really if you don’t mind.
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IIRC, eggs cells are diploid until just before ovulation. That’s when they split, forming two haploid cells. Then, whichever one matures the best is the one that’s released.
Here’s what I got so far. Correct me if I’m wrong.
The confusion Solkoe exhibited may lie in the fact that most deleterious genes are recessive, since a deleterious dominant is much more rapidly selected against, while a deleterious recessive may be masked for several generations before it happens to match with another recessive and become expressed. However, the converse is not true: most recessive genes are not deleterious. And, of course, whether deleterious or not,they generally code for something -- just not what might be useful that their dominant counterpart will.
I will assume that deletrious mean that it kills the cell.
Am I right is saying that most recessive genes are not deletrious because they are masked by a dominant gene.
I will assume that deletrious mean that it kills the cell.
Am I right is saying that most recessive genes are not deletrious because they are masked by a dominant gene?
Most recessive genes are not deletrious.
[QUOTE=solkoe]
4) Recessive genes don’t necessarily mean a non functioning protein. They could produce an altered version of the original protein. To me this is the same thing.
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If that’s the same thing then you don’t understand the process.
A recessive gene is not non-functioning. It may or may not be differently functioning. For example the gene for haemoglobin in people with thallasemia or sickle cell is actually more fucntional then the original form in the sense that it carries oxygen in addition to acting as a self destruct signal for infected blood cells. There is nothing rmeotely non-functional about such proteins, rather they ave different levels of functionality.
Nor does a recessive gene inevitably produce an altered version of the protein. n many cases the dominant allele is the novel mutation, while the recessive form is the original. For example polydactyly, ie having more than six fingers per hand, is a dominant trait. Having merely 5 fingers is recessive. Nonetheless the recessive trait is the original condition in mammals, while the dominant triat is the novel mutation.
I don’t know what percentage of recessive genes are novel mutations and which are primitive conditions but there is no reason to assume that all, or even a majority, of recessive genes produces altered proteins. It may be that a majority of dominant genes produce novel proteins and a majority of recessive genes produce primitive proteins.
A gross oversimplification. Meiosis is a four part process. The cell divides its nucleus to double its chromosome count first, so it is effectively tetraploid. Then divides its cytoplasm four times to split the DNA into 4 nuclei with half the original complement, ie a haploid nucleus.
That explanation is itself a gross oversimplification, but better than your understanding ATM
The first stage of meiosis in placental mammals takes place well before birth. At birth the ova contain cells that have already entered the first stage of meisos to produce a “tetrapoid” cell, and have partially entered the second stage where the nucleus is split for the first time.
It is no way true to say that the porcess of meiosis takes place as an adult. The process starts before birth and completes some 12- 40 years later.
[QUOTE=solkoe]
I will assume that deletrious mean that it kills the cell. Am I right is saying that most recessive genes are not deletrious because they are masked by a dominant gene.
[/QUOTE]
No, you are simply wrong in assuming that most recessive genes are deletrious. Deleterious genes tend to get weeded out of populations very fast, even when recessive. Most recessive genes are beneficial or neutral, just as most dominant genes are.
So I just started reading “Biology of Belief” by Bruce Lipton, PhD. And there on page 65: “Following enucleation, many cells can survive for up to two or more months without genes.”
(Why is removing the nucleus called “enucleation” and not “denucleation”?)
Anyway. Lipton was a serious medical researcher at one time and then had a Revelation and is writing fringe stuff now. I am so far disappointed in the book and may not finish it. But it at least had a relevant statement.
The cell can function for quite some time but as damage occurs, it’s inability to repair itself becomes a problem.
Thanks Blake
Let me try again
Here’s my take.
Lets say gene A codes for insulin. Everyone has two copies of this gene. A altered version of this gene exists that is mutated and produces an altered version of insulin. This proteins shape is not right and it does not fit into its cell receptor. A person inherits two copies of this gene and is born diabetic.
The same can be said for a myriad of other genes such as those that code collagen, trypsin, myosin or any one of thousands of necessary proteins. Two bad genes and you’re toast. This is the reason that over 50% of all pregnancies end in miscarriage.
You have mentioned several excellent exceptions to this but you have not convinced that the scenary I state above is not the norm.
[QUOTE=ftg]
So I just started reading “Biology of Belief” by Bruce Lipton, PhD. And there on page 65: “Following enucleation, many cells can survive for up to two or more months without genes.”
(Why is removing the nucleus called “enucleation” and not “denucleation”?)
Anyway. Lipton was a serious medical researcher at one time and then had a Revelation and is writing fringe stuff now. I am so far disappointed in the book and may not finish it. But it at least had a relevant statement.
The cell can function for quite some time but as damage occurs, it’s inability to repair itself becomes a problem.
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I wonder if these cells are being kept under refridgerated conditions or not. It seems a bit long. I guess a cell has enough synthesized material to keep itself going for a while.
[QUOTE=solkoe]
Close enough for now.
Yes.
Mostly. Occasionally a divergent gene will produce no protein at all.
The sickle cell example I have mentioned twice already is a very obvious example.
That can happen, or the mutated version may be a better fit than the orighional. Or it may be a slightly worse fit but still function ar reduced efficiency. Or it may function at redcued effciency for blood sugar control but also provide total immunity to heart attacks. People who inherit two copies of such genes won’t be born diabetic, they will be born mildly diabetic, or will have no symptoms but need to produce more of the protein and have other massive benefits.
No. The reason most pregnacies end in miscarriage has nothing whatsoever to do with genetics.
I never said it was the norm, I said I don’t know and there is no reaosn to believe it is the case. Neither do you. The real question you need to ask is why you believe that most recessive egnes are detrimental and novel? What evidence do you have to support his statement? Based purely on logic I would assume that this is not the case. The vast majority of alleles are not detrimental, so that alone suggets strongly that most recesive allelles aren’t detrimental.
I have presented my logic as to why I think recessive genes are detrimental.
In general, recessive genes are mutated. They may produce more useful forms of a protein but usually the mutation is detrimental. Nature selects the good over the bad and, in the end, we have evolution.
I understand that from an evolutionary standpoint, recessive genes are essential because they are the engine for change. I also understand that dominant genes can be detrimental. I understand by the idea that, by far, most recessive alleles are negative, until shown otherwise.
You seem to agree that most pregnancies result in miscarriage but you do not agree that it is due to genetices. I’m dying to get this story because I feel that I have been teaching the wrong info for so many years.
[QUOTE=Blake]
The sickle cell example I have mentioned twice already is a very obvious example.
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Sickle cell is not a recessive gene as the heterozygous condition leads to a different phenotype (malaria resistance) than either homozygous condition.
I think the simple answer to the question is that sperm and eggs don’t need every gene to work in order to do their job. A sperm does not need a functional insulin gene, or neurotransmitter-making gene in order to swim into the fallopian tubes and fertilize an egg.