Lily asked in Science & MathematicsBiology · 10 months ago

# How could the human genome be sequenced if some of our genes differ (like eye color)?

dumb question but I would really like to know the answer

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• 10 months ago

We can't pinpoint what's "different" about your particular genetic sequences until we know what "normal" looks like. We do this by sequencing tons and tons and tons of peoples' genomes and comparing them. If 999/1000 people have an A in a particular spot and you have a G, we can feel pretty confident that A is the "normal" sequence.

By doing this many times, we've built up what we call a reference genome, which doesn't match any one individual's sequence. Instead, at every position, the reference genome has the most commonly found base present. By comparing (aligning) an individual's genome to the reference genome of choice, we can identify every difference (variant) that the individual carries.

For obvious reasons, the more genomes we can use to build our reference, and the more genetic diversity we can include, the better. This is why projects like the NIH's All of Us and Iceland's deCODE are still collecting more and more.

• Anonymous
10 months ago

You are correct. Yes, eye colour is one example and don't forget male/female differences!

A genome sequence is unique to each individual (ignoring identical twins/triplets/etc.)

It is therefore technically incorrect to say *the* human genome has been sequenced. We should say *a* (or some number of) human genome(s) has/have been sequenced.

There is about a 0.1% difference between individuals' genomes (a few million base-pairs).

But saying "the human genome has been sequenced" is just an informal way of saying we know the DNA sequences for all the key attributes of a human being (plus some extra sequences for a particular individual).

• 10 months ago

Initial sequencing was done "shotgun" on samples from the "haploid reference genome."

The haploid reference genome wasn't actually from a single person.

Since then, other samples have been sequenced. Most famously, James D. Watson's genome has been sequenced. If you look around, you might find a copy of that work, and/or comparisons between his genome and the haploid reference genome.

• Anonymous
10 months ago

The genome of a single person was originally sequenced, and researchers know fully that not every person's DNA sequence will be exactly the same. it is a starting point. The sequenced genome can serve as a reference, so that other people's different genes can be compared to it.

Eye color is not a single gene. If is a combination of different factors. Blue eyes is the result of a lack of pigments inside the eye. The eyes of all people have the same molecules and these molecules scatter blue light, in much the same way that the sky looks blue because the air molecules scatter blue light. The eyes of most people around the world are brown because they have the pigment eumelanin inside the eyes, which absorbs all kinds of light, including blue. Blue eyed people have a defective version of the gene(s) that is responsible for making eumelanin. Without eumelanin, the scatterd blue light is not absorbed, and can be seen by other people. Since it takes several steps to make eumelanin, and each step requires a different enzyme, it means there are several different genes that can result in blue eyes if any one of them is defective. One person with blue eyes may therefore have a different defective gene than another person with blue eyes. Blue eyes are rare among non-Europeans, but it is known and these people may have a different reason, a different defective gene, than Europeans who have blue eyes. Hazel eyed people do not have eumelanin in their eyes, but they do have a large amount of phaemelanin in their eyes. Pheomelanin looks yellow in low concentration but red in high concentration. People with no eumelanin but a small amount of phaemelanin inside the eye will have green eyes because yellow + blue = green. In contrast blue-eyed folks have neither eumelanin nor phaeomelanin inside their eyes.