<p>6th grade girl keeps asking me this question: genetically, who is closer, siblings, or parent and child? And this one: genetically, who is closer to you, your child or your parent? </p>
<p>I gave her an answer, but now I'm thinking I told her the wrong thing. Can any of you smart parents help me out?</p>
<p>This may be moved to the Cafe, I suppose, but I thought I'd try it here.The Cafe just makes me nervous, as does posting on any of the student threads (though I do it from time to time).</p>
<p>They are the same!
siblings have 50% of their genes in common and parent/child have 50% of their genes in common
aunts uncles nieces nephews and grandparents would have 25% common genes
first cousins would have 12.5% genes in common</p>
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genetically, who is closer, siblings, or parent and child? And this one: genetically, who is closer to you, your child or your parent?
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<p>My answer would be, siblings are closer to each other because they both have genes from the same pool, ie 50% from the father, 50% from the mother. The extreme obvious case would be identical twins. They are obviously closer genetically to each other than one parent is to either. Second question, I would answer your child and your parent are both equally close to you genetically. </p>
<p>My answers = my guesses... I am not a geneticist.</p>
<p>genes are a little more complex than that.
Example I have red hair.
Neither my parents or my sibs had red hair, my great grandfather did.
Brown is dominant over blonde, blonde dominant over red.
My dad had brown hair ( apparently a brown gene and red gene)
My mom had blond hair ( a blond gene and a red gene)
( little more complex than that but you get idea)
The only way red hair could be expressed is if I received the red gene from both parents. My siblings have blond hair.
My sister whose husband has red hair, has 2 kids with red hair.
My brother whose 1st wife had blond hair, has two kids with blond hair.
His 2nd wife has brown hair and he has one with brown hair as well.
My husband has blond hair, and he has one sib with blond hair, and one with brown.
Our kids both have blond hair, the only gene I can give them is red, the only gene my husband can give them is blond, blond is dominant, but they could theoretically have kids with red hair if they married someone with red hair, or brown ( with recessive red gene)</p>
<p>Siblings can have all their genes in common, or none of their genes in common. Or anything in between. </p>
<p>Parents always have 50% of their genes in common with their children.</p>
<p>To clarify on siblings: every time an egg or sperm is made, the genes from that parent sort 50-50 and only half are used from each parent. Thus, a parent who is Aa could contribute an "A" to an egg one time and a "a" the next time, with the other parent doing the same with his contribution to the two sperm.</p>
<p>Thus, the two kids could be AA and aa and share no genes, while each parent shares 50% with the kids.</p>
<p>This continues with every one of the 30,000 genes we each have.</p>
<p>Keep in mind that only dominant or mixed-dominance genes are expressed in the phenotype (what you actually see). Siblings may appear to have the same genes (both have brown hair) while one carries a recessive gene and the other doesn't.</p>
<p>Some interesting traits that are determined by genes are: which thumb you put on top when you fold your hands; which way your hair twists at the back of your head; whether you can curl your tongue.</p>
<p>Thanks dmd77 for that very clear explanation. That is what I ended up thinking (eventually, and not in a very clear way) after I told my daughter something else. I was thinking at first that siblings were likely to have less than 50% of their genes in common, making the parent and child more genetically similar, but after a while (a LONG while--good thing this wasn't an exam!) it dawned on me that the siblings could have more than 50% in common (didn't even think about the identical twins, which makes that pretty obvious), so wanted to check that somehow, and of course, I knew the people on this forum would know. At first I thought she was just curious, but she said something that makes me think she is simply looking for proof that she and one of her brothers in particular have absolutely nothing in common. Sibling rivalry at its best (worst?).</p>
<p>i was just thinking about this the other day. my little cousin that lives with me looks JUST like a little version of me - every time i take her somewhere people think she's my daughter! my own sister deosn't even look like me. i was trying to figure this out, and if the genes go the way i'm thinking, i could have 50 percent from my mom and 50 percent from my dad , my little cousin could have 50 percent from her mom and fifty percent from her dad... and since our moms come from the same parents.. (they look similar to each other, and i look similar to them) ... so does that explain why we look so much alike?
(this may be completely off, i got a C in biology ;) )</p>
<p>Speaking as a professional biologist I can promise you that the correct answer is siblings. Human siblings are always more closely related than parents/children. An easy illustration of this is the fact that organ transplants between siblings will "take" much more frequently and with fewer complications than with parent/child transplants.</p>
<p>dmd77's illustration about how siblings can share all or none of the allo-genes (genes that vary within a given species) is correct, but only in theory. In reality it never happens that way in humans - it's always somewhere in between. Due to genetic recombination mechanisms such as independant assortment of chromosomes and crossing-over between paired chromosomes, combined with the large number of genes in question, ensures that human siblings always share >50% of their allo-genes.</p>
<p>I think I read very recently about a family where the older child has a disease, and the parents had a second child in order to "harvest" things like bone marrow for the first child... Unfortunately, I don't even remember enough details to google it.</p>
<p>Tks coureur. I can't say I understand your explanation, but I'll take your word for it. All I can say is, if they have so much in common, why don't they get along better!</p>
<p>so coureur, how many allo-genes do we share with our parents? Could you share very few allo-genes with one parent? This may be a weird q, but I thought I had read years ago in National Geographic that you could share more genes with a grandparent than a certain parent...</p>
<p>The vast majority of your genes you share in common with your parents, your siblings, and everyone else on CC. Those are the genes that define you as a human being.</p>
<p>Of the small minority of genes that vary within a given species (the allo-genes), you get 50% from each parent. Actually, you do get a handful more from your mother than your father in the form of the mitochondrial DNA, but for all practical purposes it's 50% from each parent. You get 25% of your allo-genes from each of your grandparents. In a normal outbread human population it is not possible to be more closely related to a grandparent than to a parent. </p>
<p>In inbred mice and rat strains the animals can be equally related to their parents and grandparents, since the entire population is genetically identical, but that does not apply to humans.</p>
<p>We needed to be tested for bone marrow/stem cell transplant possibilities and number of years ago. For transplant purposes, the immune system need to be the closest match as it is the watchdog for the body in keeping intruders out. A mismatch in such a transplant brings about a reaction called graft vs host which can be fatal and is very nasty. This is when the graft (the immune system) which is transplanted rejects the host (the body) and is the opposite of what happens in organ transplants where it is the body that tries to reject the transplanted organ. </p>
<p>Each of us, H and I were half matches to our son in need. But only one out of the 4 natural siblings was a full match to him. So in that particular case, my D and that son were full matches, and therefore closer genetically to each other than my H or I. The other two brothers were not a match. This is the same DNA testing that is done to identify people, I understand. So two brothers with the same HLA type (that is the term they used) could be genetically indistinguishable--the same with any full bone marrow transplant match, related or not, though sex and blood type also are factors there--because my D and S are not of the same sex or blood type, they were easily distinguishable even though they have identical HLA types and considered "perfect" matches. </p>
<p>So it is possible to be siblings and not have any similarity in HLA types since each parent has two types and you inherit one allele from each parent and there are 6 alleles in pairs. And parents can be closer matches to a child than the siblings, especially if the two parents have some of the same alleles. I have seen parents who were 5 point matches to their kids and it is possible for them to be perfect matches as well. There is still even a bit more to it than that , but that is essentially the way we define genetic or DNA matches.</p>
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<p>And parents can be closer matches to a child than the siblings, especially if the two parents have some of the same alleles.<<</p>
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<p>Jamimom,</p>
<p>This is true, but you should not infer the overall degree of genetic relatedness between siblings and/or parents from better or worse matches of the HLA type. The HLA type only describes the match at one small set of genes (albeit a very important set for transplantation purposes). The same random assortment of genes that occurs for the HLA genes happens a thousand times over for all the other allo-genes. Stated another way, thanks to all these other genes that they share, two brothers who are a complete HLA mismatch are STILL more closely related to each other than they are to either of their parents. And conversely, two completely unrelated individuals, even of differing races, can by chance be a total match at the HLA locus.</p>
<p>Agreed, Coureur. The HLA locus is not the whole picture, though the chances of two completely unrelated individuals of differing races having a perfect match are very small as HLA types are racially andn ethnically governed. You can pretty much come up with a racial id with HLA typing. That is why when they do bone marrow drives they often focus them on the ethnic group of the recipient. </p>
<p>The whole question of genetic exactness is interesting. When I saw the pictures of the cloned cats, the most striking thing immediately noticeable was that they did not look alike! Cloned but not identical? With sheep since they all looked the same you did not see that possibility but with cats with more variance, it comes up. And my kids who are the HLA matches do not look alike at all. One dark, one blonde. Not much rememblence in facial features either, nor in build.</p>
<p>I saw your previous post and I was wondering if you could answer some questions about bone marrow donating for me (or even direct me to a website where I could find more info.) </p>
<p>How would someone go about donating?
Can a non-family member donate, or even be a match for a recipient?
Are there expensive testing or medical costs for the donor?
Where would someone go to donate?</p>
<p>Exact HLA matches between unrelated individuals of different races are rarer than exact matches within a race, but by no means are they unheard of. The research I do at work involves knowing the HLA types of the cells being used, so nearly everyone in the building (~100 people) including me has been HLA typed as potential blood donors for the experiments, and we have some exact matches in the building including at least one cross-racial one. This is due to the fact that some alleles are common in several races. E.g. HLA-A02 the signature allele for caucasians (found in about 40%) is also fairly common in Asians and Africans (~ 15-20%). So if you've got a haplotype consisting of these common cross-over alleles, an exact cross-racial match is a decent possibility.</p>
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<p>And my kids who are the HLA matches do not look alike at all. One dark, one blonde. Not much rememblence in facial features either, nor in build.<<</p>
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<p>Yup, exactly my point. The HLA is just one locus out of thousands of genes and matching or not says almost nothing about how closely-related you are. Unless they are adopted, your kids are all equally closely related to each other regardless of whether their HLAs match. Same with your kids who are blond or not. Two blonds who are siblings are just as closely related to their brown-haired brother as they are to each other (unless we are talking identical twins).</p>