DNA Day experts answer your questions about chromosomes

CurioCity
18 April 2013

If red blood cells do not have a nucleus, where do the chromosomes go? Are you able to do DNA analysis on red blood cells then?

DNA analysis? Not really, the only DNA in the red blood cells is the ancient 0.0002% of the genome called the mitochondrial genome (used for energy production). The DNA doesn't go anywhere...the red blood cells spawn from special mother cells that don't replicate their DNA, as would normally happen during cell division.

- Answer provided by Dr. Paul Gordon

A bacterial chromosome was made in vitro. Do you know if the bacteria survived and if so, how long?

Yes it did survive for a number of generations (if it is the experiment I'm thinking of). Plasmids, which are extrachromosomal pieces of DNA are usually made in vitro and we can use bacteria to grow up large amounts of DNA.

- Answer provided by Dr. Dennis McCormac

I was wondering which chromosome is affected in Huntington's Chorea?

Huntington's Chorea is an unusual genetic disorder caused by an excessive repetition of a segment of DNA. Chromosome 4 is affected, where a segment of DNA that is normally repeated 10-28 times is now repeated 36-120 times.

- Answer provided by Dr. Karen Bedard

Does chromosomes number noticeably affect the mass of DNA?

Certainly. The more chromosomes a cell has means more DNA. We can even see this as cells move through the cell cycle. A cell in G1 phase (before DNA replication) has half the mass of DNA that a cell has in G2 phase (after every chromosome has been duplicated, but before actual cell division).

- Answer provided by Dr. Aaron Goodarzi

Is there a specific way to group chromosome pairs in a karyotype?

This is outside of what I do routinely, but if I understand your question, the Chromosome pairs are grouped based on size, with 1 being the largest.

- Answer provided by Dr. Karen Bedard

How is it that transposons are able to jump between chromosomes? Will we one day be able to harness this movement to our advantage?

Many transposons resemble viruses and like viruses are able to use the molecular machinery of the cell to reporduce themselves and "jump" from chromosome to chromosome. At one point, we thought we might be able to use that system, like we thought we could use viruses, to insert DNA into the human genome. For example, to insert a "good" copy of a gene into someone's genome that only had a "bad" copy. The problem is that the insertion is largely random and the insertion itself causes mutation - can disrupt genes, etc. We use similar gene disruption lines in my lab. There are "better' systems out there now that will likely allow us to more specifically insert DNA into a genome, with fewer unexpected side effects. We can use this new technology now in many model systems including monkeys. Its likely that these more specific systems are the future of this kind of genetic engineering in humans.

- Answer provided by Dr. Thomas Merritt

What type of organisms have single-stranded chromosomes (only 1 chromatid)? Is there an evolutionary benefit to having double stranded chromosomes (2 chromatids)?

Stranded isn't quite the right term. All DNA (mostly) is double stranded. I think you mean pairs of chromosomes, diploid, versus single chromosomes, haploid. Bacteria tend to be haploid, eukaryotes tend to be - but not all are - diploid. Two copies of the chromosomes allows multiple alleles in a single organism - and interchange between the copies. In sexual reproduction, this exchange allows for recombination and more complex combinations of the genetic diversity that is out there. Haploid genomes - however - tend to be really fast to replicate. Fast DNA Replication means fast reproduction - and fast reproduction is the name of the game for bacteria. So - diploid - complex. Haploid - fast.

- Answer provided by Dr. Thomas Merritt

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