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#1
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Questions about alleles and genes
Give that alleles are different codings of the same gene - does that
mean the different alleles are the same length? It must also be true - right? - that different alleles encode for different proteins (else there would be no difference in their manifestation.) Assuming two samples of DNA could've - but not necessarily - come from different species, if at a particular locus the DNA is different, how does one know if the difference distinguishs different alleles or different genes? . Thanks. |
#2
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Questions about alleles and genes
In message .com,
Raphanus writes Give that alleles are different codings of the same gene - does that mean the different alleles are the same length? It must also be true - right? - that different alleles encode for different proteins (else there would be no difference in their manifestation.) Different alleles are often, but not universally, of the same length. In some cases they are distinguished by one or more base pair substitutions. In others they are distinguished by the insertion or deletion of lengths of DNA. Alleles don't always code for proteins - apart from ribosomal and transfer RNA genes there are also bits of DNA which represent regulatory sequences rather than protein, and other odds and ends. It is possible for one allele to represent the absence of the gene; in the case it obviously doesn't code for a program. In other cases the protein product may be the same, but modifications to regulation have changed the amount produced. Assuming two samples of DNA could've - but not necessarily - come from different species, if at a particular locus the DNA is different, how does one know if the difference distinguishs different alleles or different genes? . With difficulty. If the genes are orthologous and functional then the amount of difference between the genes (for that particular locus) is a strong hint as to whether they come from the same or different species. However the existence of paralogs and pseudogenes means that this assumption cannot be relied on. [Orthologs are the "same" gene in different lineages; paralogs are genes which descend from different branches of a gene duplication event. For example haemoglobin alpha and haemoglobin beta are paralogs; human haemoglobin alpha and chimpanzee haemoglobin alpha are orthologs (and, IIRC, in this case, identical).] Thanks. -- Stewart Robert Hinsley |
#3
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Questions about alleles and genes
Stewart Robert Hinsley wrote: In message .com, Raphanus writes Different alleles are often, but not universally, of the same length. In some cases they are distinguished by one or more base pair substitutions. In others they are distinguished by the insertion or deletion of lengths of DNA. OK. Now in a heterozygous gene the two alleles would have to be of the same length - right? Otherwise there would be a "kink" in one strand of the DNA spiral (?). I appreciate your answers. They give me much to "chew on." |
#4
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Questions about alleles and genes
Stewart Robert Hinsley wrote: Different alleles are often, but not universally, of the same length. In some cases they are distinguished by one or more base pair substitutions. In others they are distinguished by the insertion or deletion of lengths of DNA. "Raphanus" schreef OK. Now in a heterozygous gene the two alleles would have to be of the same length - right? *** Why? * * * Otherwise there would be a "kink" in one strand of the DNA spiral (?). *** Why? * * * |
#5
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Questions about alleles and genes
In message .com,
Raphanus writes Stewart Robert Hinsley wrote: In message .com, Raphanus writes Different alleles are often, but not universally, of the same length. In some cases they are distinguished by one or more base pair substitutions. In others they are distinguished by the insertion or deletion of lengths of DNA. OK. Now in a heterozygous gene the two alleles would have to be of the same length - right? No. Otherwise there would be a "kink" in one strand of the DNA spiral (?). No. I think you're confusing diploid genomes with double helices. The two alleles in a diploid genome are on different chromosomes (DNA molecules plus associated proteins). Sometimes there are multiple copies of a gene on a single chromosome (for example the ribosomal RNA arrays), but they're not in the same position on opposite strands. One strand has coding (or junk) DNA, and the other has complementary DNA. (Different genes can be on different strands.) To a first approximation both strands are the same length; in particular a deletion or insertion occurs on both strands. The function of the complementary DNA is to act as a template for replication of the coding DNA. I appreciate your answers. They give me much to "chew on." -- Stewart Robert Hinsley |
#6
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Questions about alleles and genes
Do not the ends of the paired alleles have to coincide? Or can one
complete strand of DNA within a chromosome be longer than the other? P van Rijckevorsel wrote: Stewart Robert Hinsley wrote: Different alleles are often, but not universally, of the same length. In some cases they are distinguished by one or more base pair substitutions. In others they are distinguished by the insertion or deletion of lengths of DNA. "Raphanus" schreef OK. Now in a heterozygous gene the two alleles would have to be of the same length - right? *** Why? * * * Otherwise there would be a "kink" in one strand of the DNA spiral (?). *** Why? * * * |
#7
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Questions about alleles and genes
Stewart Robert Hinsley wrote: No. I think you're confusing diploid genomes with double helices. You're right. Sorry about that. |
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