Hot answers tagged

29

Firstly, it's not true that you can't tell racial background from DNA. You most certainly can; it's quite possible to give fairly accurate phenotypic reconstruction of the features we choose as racial markers from DNA samples alone and also possible to identify real geographic ancestral populations from suitable markers. The reason that human races aren't ...


27

Well, that's just it, we don't actually have much phenotypic variation. For example, compare this: to this: or this: Or this: to this: This is phenotypic variation: And of course, you can't beat the birds of paradise when it comes to variation (though, strictly speaking, these are different species): So, as I hope is clear from ...


24

The uniqueness of irises and fingerprints are, as you said, limited to the number of possible permutations of irises and fingerprints. A similar problem exists in computer science, and is known as a hash collision. Given sufficient samples, there will always be a collision for a hash of finite size. However, the sample space is sufficiently large for iris ...


17

The first modern humans evolved about 200.000 years ago in Africa. When they lost their body hair (or at least most of it), they needed some other protection of their skin from the sun - otherwise they are prone to develop melanoma. Melanin is such a protection, and the rate of melanoma is much lower in dark skinned people. There is also a nice correlation ...


15

Actually it is a very important question for laboratory animals (and, I imagine, endangered species) and was calculated to be 25 couples. With any number of animals (including humans), there is always some inbreeding happening, but you can reduce it with the number of breeding pairs and careful pairing. When you get to 25 pairs (50 animals) and have ...


12

Bone Marrow transplants are extensively matched in order to prevent rejection. Current matching methodology is HLA matching: Stanford Children's Hospital Guidelines How are a donor and recipient matched? Matching involves typing human leukocyte antigen (HLA) tissue. The antigens on the surface of these special white blood cells determine the genetic ...


12

According to wikipedia, "comparisons between known skin pigmentation genes in chimpanzees and modern Africans show that dark skin evolved along with the loss of body hair about 1.2 million years ago and is the ancestral state of all humans." This is several million years after after the time estimated for the last common human-chimpanzee ancestor, but at ...


12

This is an interesting question, and there are a number hypotheses available to explain this phenomenon. The short answer (as far as I can say this after my literature search) is that we don't know the answer for sure. The long version follows below. The main problem with all these hypothesis is that they have some valid point, but a definitive hasn't been ...


12

Note: This is based on literature searches I've done a while ago out of general curiosity. I'm in no way an expert on human reproduction. First, I'm not sure if you are asking about evolutionary reasons or the developmental causes for for a difference in sex ratio. Here, I will focus on the developmental causes. There is much evidence for a male bias in ...


11

I thought it was just that the other aneuploidies were fatal. They occur as often but miscarry earlier in the term therefore you don't see them. So basically there are only three that are viable 21,18 and the sex chromosome with a number of combinations: XO, XXY, XYY and XXX. More information here: ...


11

"Blame" is a strong word. The human Y chromosome has only a few dozen protein-coding genes. One of the most important, for males anyway, is SRY, the sex-determining region. This is a transcription factor that is responsible for modulating the expression of other genes; those genes need not be on the Y chromosome. SOX9 for example is itself a ...


11

...would then be his offspring at risk? Why? No. Generally speaking, fathers do not pass on their mtDNA (Mitochondrial DNA). Why? Because the mitochondria present in oocytes (egg cell) is the mother's, as every oocyte directly inherits the mother's mitochondria when they are made in the reproductive organs. The mitochondria that the sperm from the ...


10

People can grow taller than their parents. Anecdotally: I'm 185 cm, my parents are 155 cm and 178 cm. Joakim Noah, an NBA basketball player is 211 cm, his dad was 193 cm and mother was 175 cm... how? Genetics and environment play a role in determining height. First of all, a more nutritious environment during development can lead to increased height, this ...


10

A gene being dominant does not necessarily imply the gene is also common. An easy counterexample is Huntington's disease. The gene is dominant, and only one mutant allele of huntingtin would result in development of the disease. However, the allele prevalence of the mutant is low in the general population. In the absence of a selective advantage of green ...


9

The concept of a human/chimp hybrid is called a humanzee. No humanzees have ever been recorded despite the fact that sexual intercourse between humans and chimps has been recorded on several occasions. This suggests that male-human/female-chimpanzee is not capable of producing viable offspring, at the very least. As to why, several reasons will contribute: ...


9

The maternal and fetal blood circulation systems are completely separate. The embryo's blood cells start developing at around week 5 gestational age (3 weeks after conception), the same way any other tissue is developed by the fetus itself. By around week 7 gestational age, a circulatory system has developed and the heart has started beating. All nutrition ...


8

This difference would have the greatest impact on treatment for cancer, in which a treatment protocol is based on genes deleted, amplified, altered in the tumor vs the reference genome for that patient. In terms of health risks based on SNP genotypes, the data are far from complete. Sure, some level of risk can be assigned to a variant (SNP), say at certain ...


8

I very much agree with bitwise's answer. I just want to point out that even in terms of nucleotide sequence there are some extremely conserved genes. The most highly conserved are ribosomal RNA genes. The image below shows the conservation of 16S rRNAs from archaea, bacteria, and eukaryotes (eukaryotes do not have 16S in their cellular genome but the gene ...


8

Hair color is not so simple as that. Most traits, especially those as complex as color, are controlled by many alleles at many loci. That's why there are different kinds of brown, blond, and red hair in the population. There is no "hair color gene." A fascinating paper came out a few years ago, identifying dozens of SNPs playing a role in hair and eye ...


8

"How come most animals never seem to evolve over millenia?" The word "seem" in your question should not be disregarded. You seem to assume that cockroaches (or most animals as you say) did not change much the last tens or hundreds thousands of years. But what do you know about that? Have you actually reviewed many research that estimate the rate of ...


8

There are many different variants of O (all loss-of-function) indicating that this mutation has arisen many times in the human population. The prevalence of O is indeed taken as evidence of balancing selection. Various pathogens use the A or B antigens as receptors. The cited paper presents evidence about the phylogeny of the ABO gene in human populations ...


8

When you bend your fingers, they all arrive at the same height. I would tend to think that their lengths differ when you keep them straight because they need to have similar length when you bend them. And I guess that there is some optimal length (when bended) for fingers to grasp things. It is nothing but a quick hypothesis. But it sounds quite plausible ...


8

Presumably this means that at least some grey haired humans have noticeable reproductive advantage, or maybe they had it in the recent past. No it doesn't. Natural selection is not that strong, it doesn't optimize every single possible physical trait towards maximum reproducing. And as others have mentioned, having lots of grey hair usually ...


8

If you with 'humans' refer to our genus Homo (which is often the case), we do have multiple species, see wikipedia for an overview. The difference to many other organism groups is just that all species except Homo sapiens are extinct. Also, taxonomic ranks below the species level - such as breed, subspecies, population and race - are very poorly definined ...


7

Gene frequencies (frequencies of each allele at a given loci) in populations are affected by many things divided in to systematic and dispersive processes. Systematic process (migration, mutation, selection) affect gene frequencies in an often quite predictable manner and strength. Dispersive process (Random drift, differentiation between sub-populations, ...


7

Depends on what you mean by unchanged. If you mean a gene that maintained the same nucleotide sequence, then the answer is no. If you meant a gene that descends from a very ancient gene, i.e. one can find orthologs in very distant species, then the answer is yes. Many of the basic molecular systems are relatively conserved, including several metabolic paths ...


7

That would be hard to say because really beneficial mutations become well distributed through the genome. Basically the differences between us and chimpanzees are a catalog of all the beneficial (or completely neutral) mutations since the ~4.7 M years since we diverged from each other. Separating them from changes which have no special effect would be ...


7

The processes that control the germline of metazoans (multicellular animals) are highly regulated compared to single cell bacteria and eukaryotes as well as plants. At this point there are no clear stories of gene transfer into a complex animal, though there are some for plants: "animals and fungi seem to be largely unaffected, with a few exceptions, ...



Only top voted, non community-wiki answers of a minimum length are eligible