April 22, 2008

Genes and Dominance

Posted in Genetics tagged , , , , , , at 10:45 am by D. Borst

Why are some genes recessive?

So in genetics class, we learn that Mendel began the study of genetics with his study of peas. One of the notions that he developed was that of Dominant and Recessive genes. But in this age of molecular genetics, what does it mean to be dominant or recessive?

Further inquires into the topic have also led to more controversy. Some genes are “incompletely dominant” and some share “codominance.” Mendel’s Law of independent assortment turned out to not be entirely true. Some traits seemed to be inherited only from the mother.

On the other hand, the discovery that we have a diploid genotype provided a very obvious explanation for the presence of two alleles of a gene, and the nature of meiosis explains why alleles separate during the production of gametes. Today I want to focus on what factors, from a molecular biology standpoint, produce genes that act recessive and dominant. The key is the level of expression.

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April 18, 2008

Differences between the molecular biology of Prokaryotes and Eukaryotes

Posted in Microbiology tagged , , , at 10:28 pm by D. Borst

So Molecular biology is still progressing pretty slowly, and today we
just focused on basics of molecular biology, but we did cover some of
the differences between prokaryote and eukaryote genetics.

The most obvious difference between the two is that prokaryotic DNA
is generally arranged into circular structures, while eukaryotic DNA
is arranged in linear strands. Furthermore, eukaryotic genomes
contain multiple chromosomes, while prokaryotic genomes only contain
one. This difference may be a result of the massive bloat that has
occurred in eukaryotic genomes. While eukaryotic genes tend to be
longer and more complex than prokaryotic genes, they are also only a
fraction of the total length of the nucleic acid strand. Prokaryotic
genomes are up to 90% coding sequences, while coding sequences in
eukaryotic organisms is often around 3%. Furthermore, eukaryotic
genes are peppered with introns, spans of non-coding sequences within
an operon, while prokaryotic genes are generally free of such nonsense
sequences.

All of this means that eukaryotes tend to have much more DNA than
prokaryotes. One explanation of the difference in the morphology of
the DNA is simply that as the length of the nucleic acid sequence got
longer, it got too long to be effectively manipulated as a single long
loop. Read the rest of this entry »