What Are The Differences Between The Dna Sequences Of Two Alleles Of A Gene
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8.1 years ago
jack ▴ 490

Hi,

in diploid organisms like human, they have two sets from every chromosomes.as I figure out the sequence of these two sets are similar. (for example sequence of two chr1). but what are the differences between sequence of a gene in Alleles form like AA, Aa, aa ? are the difference in the promoters or in the coding regions ?

genome genomics genetics bioinformatician • 28k views
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They can differ anywhere. Or are you asking how to annotate differences with whether they're in coding/promoter/etc. regions?

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Yes, and I want to figure out for example how much is the diffrences between A and a .

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"how much is the differences between A and a" isn't a coherent question.

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They can differ in just one base (e.g. A->T at certain position) as well as on multiple locations. You may not only observe single nucleotide variants, but also insertions or deletions or other rearrangement. How much they will differ is gene-specific.

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8.1 years ago

If a gene has two alleles, these alleles will be different at the nucleotide level. This difference can be some form of sequence or structural variation. For example 'AA' means homozygous alleles and if you are talking in context of genes then both the chromosomes will have identical nucleotide copy of a gene. 'Aa' means heterozygous alleles. 'A' and 'a' correspond to the same gene but their nucleotide content differ with each other by one or many sequence variants (SNPs, Indels). For example, 'A' can be 1000 bp gene and 'a' can be 1200 bp gene with extra 200 bp of some kind of repeat. These differences can occur in both coding and non-coding regions. For example, promoter etc. Also, not all the times different alleles will result into difference at the phenotypic level.

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great explanation ! :-) . thanks

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8.1 years ago

Are you in high school?

You should keep in mind that the high school Mendelian paradigm you learn, where a noticeable difference in phenotype can be explained by looking at a single gene, with two alleles in a given population, where one allele is totally dominant to the other...that model is just a model, and while it explains some scenarios in biology well, the vast majority of phenotype-genotype interactions that people study are much more complex than that.

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yes, ok, so how is it so work ? I mean if the Mendelian paradigm is not completely correct, what's make an allele dominant to other one?

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Mendelian paradigms are correct for explaining some things. Like tongue rolling. Just not a lot. Even eye color is more complicated than blue/brown, right?

In most cases, two alleles can't be properly classified as 'dominant' or 'recessive' to each other. The alleles causing A and B blood types aren't classically dominant or recessive with respect to each other, right?

There are 30,000 genes in the human genome. There are a lot of alleles observed in the whole human population. If high school has led you to think that all those possible alleles, and phenotyping possibilities can be explained with simple Punnett squares, because those are the only kinds of homework problems that can be assigned and solved, well, that's just not so. That paradigm is not generalizable to every single biological scenario, so when you ask in a general way to explain the differences between alleles, there is no general answer that can be given.

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Isn't 30k too much.. or are you counting isoforoms as well?

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