49
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 ...
35
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 the images above, ...
33
It is true that the Y chromosome is shorter than the X chromosome and that there are more genes on the X chromosome.
Do men have fewer genes?
One could (mis)understand three things in the expression "number of genes".
Number of gene copies (see Copy Number Variation)
Number of genes
Number of alleles
Thanks to @GerardoFurtado for correcting my ...
31
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 ...
24
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 ...
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 ...
22
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 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 hypotheses is that though they may have a valid point, a definitive hypothesis ...
21
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 ...
20
Neandertal DNA has been completely sequenced multiple times now, using DNA from bone and tooth samples found in cool or cold environments. The first Neanderthal genome sequence was described in 2010:
A Draft Sequence of the Neandertal Genome
Since then, as well as higher-quality sequence, more genomes have been completed; at least 6 individuals have been ...
19
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 ...
19
Short answer:
Chimpanzees are indeed closer, but perhaps...too close. Almost all invasive research on non-human great apes has halted for some time over ethical concerns.
Rhesus macaques are the main non-human primate still used in research (some others are also used, like marmosets). "Pretty much the closest" is in reference to which species are available ...
16
How come most animals never seem to evolve over millennia?
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 of thousands of years. But what do you know about that (no offence here)? Have you actually reviewed many kinds of research that ...
16
I decided to summarize a competing hypothesis to make our answers more balanced. I also tried to address the question about the degree of human morphological diversity compared to other animals.
According to Woodley (2010), it is plausible that H. sapiens does not belong to one species and subspecies (i.e. is polytypic). Some of the data he uses to support ...
16
The answers here give you reference to the first draft genome. Take a look at these papers for high-quality sequences: Prufer et al., 2014 for Altai Neandertal, Meyer et al., 2012 for the Denisova individual. A third one, the Vindija Neandertal has been sequenced and the sequence is already available (though not published, yet) here. However, one thing has ...
15
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 ...
15
Good literature work here and good question +1! In short, your main mistake was that you based your calculations on a single site and not on the whole genome. More info below.
Genome-wide vs sites specific mutation rate
The statistic of $10^8$ generations that you computed is the average rate of fixation of new neutral mutations per site. As considered the ...
13
In a genome that is 3 billion base pairs, a difference of 0.5% works out to a difference of 15 million bases. When a single base change can change the amino acid sequence of a protein, that can add up to a huge amount of diversity, which is what we see over the nearly 8 billion humans on the planet, and the 99.5% sameness is why we are linked together so ...
12
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:
http://www.nature.com/scitable/topicpage/chromosomal-...
12
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 ...
12
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 ...
12
Are males taller than females?
Best data I could find come from the Statistical Abstract of the United States (1999) > Section 3. Here is a table reporting the percentage of the male and female population which height is lower than a given threshold
Note that this data collection was done among students in US universities and is therefore not ...
11
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 have 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: ...
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
Bias
When you say phenotype you mostly mean "skin color", "size of the nose", "hair color", "shape of the eyes", "height", and some others. All these traits that we manage to find to explain population structure among humans. But you forget all the rest of the phenotypic diversity. If you would choose 1000 randomly chosen traits (external morphology and ...
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 father ...
11
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 ...
10
It seems to me that many answers to this question suffer from the nasty habit of "political correctness". As a zoologist, I never heard of somebody sequencing the whole DNA of any species to decide when to use or not the term "race". If a group of animals comes from a side of a river, and the other comes from the other side, and they have one or a few ...
10
According to this powerpoint from the SIU School of Medicine:
Right handed supercoiling = negative supercoiling (underwinding)
Left handed supercoiling = positive supercoiling
And from this Boston University webpage:
If DNA is in the form of a circular molecule, or if the ends are rigidly held so that it forms a loop, then overtwisting or undertwisting ...
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