A To Z Challenge: Y Chromosome And Your Ancestors

Human telomere structure, via Wikimedia Commons, Public Domain image

Like "W", there are no corresponding scientific fields that begin with the letter "Y". Hence, I'm posting about another specific section of study (a repeat from last year, I'll admit).

The Y chromosome is one of two sex chromosomes and contains over 59 million DNA base pairs, constituting almost 2% of total DNA in human cells. Sex chromosomes determine gender, of course--in normal cases, everyone has a pair of chromosomes, either XX (female) or XY (male). Occasionally there are cases of 48,XXYY (an extra pair of XY), 47XYY (extra Y), and 46,XX (fetus is male despite having female chromosomes due to an abnormal exchange of DNA).

A recent development involving the Y chromosome is the discovery that the most recent common ancestor of the Y chromosome--of which all current male genes are descended from--is thought to have lived 338,000 years ago. This is significantly before the oldest dated human fossils. The Y chromosome can be tracked because of the way it's transmitted, since it doesn't exchange as much genetic material with other chromosomes. Female XX sex chromosomes swap information; male XY chromosomes cannot since X and Y are limited in their compatibility.

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Sources:
http://ghr.nlm.nih.gov/chromosome/Y
http://ghr.nlm.nih.gov/handbook/basics/chromosome
http://www.genetics.edu.au/Information/Genetics-Fact-Sheets/Genes-and-Chromosomes-FS1
http://www.sciencedaily.com/releases/2013/03/130305145821.htm

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I can't believe it's the penultimate day of the A to Z Challenge. Are you looking forward to the end of the month? Will you miss the Challenge?

And what fascinates you the most about human history?


-----The Golden Eagle

A To Z Challenge: Karyology And Why Your Genes May Be Patented

Karyology is a field involving an organism's cell nucleus, particularly its chromosomes. It is a branch of cytology--the study of cell function and structure--which is in turn a branch of biology. Technically the word karyology refers only to the physical presence of the nucleus and its components, excluding the study of how chromosomes control in different parts of the body.

Chromosomes are tightly wound coils of DNA. As you've no doubt heard or read, DNA is the fundamental building block of life on Earth; it is the instruction manual that tells organisms how to grow, survive, and reproduce.

My next point is not strictly a scientific development, per se, but I thought it was an interesting (and perhaps alarming) recent event related to the field. This April, on the 15th, the US Supreme Court will hear a case about patenting genes. Myriad Genetics discovered genetic mutations on BCRA 1 and BCRA 2 genes--mutations related to breast and ovarian cancer--in the 1990s and filed for a patent on DNA with those mutated sequences. They got the patent.

The upcoming argument in the Supreme Court is over the functionality of the DNA. The DNA Myriad Genetics patented is, officially, "isolated DNA", which means it has to be a single piece of genetic material outside the rest of the chromosome for it to fall under the patent. The Supreme Court will decide whether the DNA is functionally different from that in the human body--there is a "products of nature" doctrine which states that something with no "marked difference" to something naturally occurring cannot be patented.

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Sources:
http://www.thefreedictionary.com/karyology
http://www.thefreedictionary.com/cytology
http://stalikez.info/fsm/semp/site/caryo_gb.php
http://www.news-medical.net/health/What-is-a-Chromosome.aspx
http://www.genome.gov/Glossary/index.cfm?id=33
http://www.sciencedaily.com/releases/2013/04/130412084225.htm
http://www.slate.com/articles/news_and_politics/jurisprudence/2013/04/are_your_genes_patented_the_supreme_court_will_decide_if_they_can_be.html

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Do you think genes should be patented? Or do you think patent offices should not allow specific DNA sequences to be "owned" by companies?


-----The Golden Eagle

A-Z Blogging Challenge: Y Chromosome

The Y chromosome.
Public domain image.
SOURCE.

The Y chromosome is one of two human sex-linked chromosomes.

To partly continue yesterday's post about the X chromosome (though reading that one isn't absolutely necessary, in case you're wondering), the Y chromosome, unlike the X chromosome, is associated with males, since males are XY and females are XX. The Y chromosome has around 58 million DNA base pairs (opposed to the X's 155 million), 70-200 genes, and makes up about 2% of all DNA.

95% of the Y chromosome is male-specific, although sections called the pseudoautosomal regions have identical counterparts on the X chromosome. Because of this, only pseudoautosomal regions can exchange places in a process called recombination (which occurs between all of the two X chromosomes in females) and male offspring possess an almost identical copy of their father's Y chromosome.

Conditions that can result from changes in the Y chromosome include 48,XXYY syndrome (where there is both an extra X and an extra Y chromosome in males) and 47,XYY syndrome (where there is the normal one X chromosome, but two Y chromosomes).

A graphic example of 47,XYY syndrome, with a male on the left
and female on the right, by Silver Spoon and Lucas Zienius,
CC-BY-SA-3.0. SOURCE.

As I was researching this post, I also found that there was a good deal (as in, webpage after webpage) of speculation that men would start to die out, since the Y chromosome shrank from being identical in size to the X chromosome to its current state of having fewer than 10% of the number of genes on the X.

However, this is theory has been rather debunked by the finding that no Y chromosome genes have been lost for six million years, and that the Y chromosome evolves rapidly. So, it seems half of the human race is genetically safe. (The chances that humanity will survive for another six million years might be far off, anyway.)

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Sources:
http://accessscience.com/content/Sex-linked-inheritance/617600
http://www.bbc.co.uk/news/science-environment-17127617
http://ghr.nlm.nih.gov/chromosome/Y
http://www.nature.com/nature/journal/v423/n6942/full/423810a.html
http://news.sciencemag.org/sciencenow/2010/01/13-03.html
http://psychology.about.com/od/yindex/g/def_ychromosome.htm
http://www.sciencedaily.com/releases/2012/02/120222154359.htm
http://www.thefreedictionary.com/Y-chromosome
http://www.ucl.ac.uk/tcga/ScienceSpectra-pages/SciSpect-14-98.html
http://www.wisegeek.com/what-is-a-y-chromosome.htm

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I hope I've made this part of chromosomal biology interesting for you all. Though if not, I hope you'll come back on Monday anyway in which I address a topic that's easier and allows for some great (in my opinion, at least) photographs. ;)


And since it's the second-to-last day of the Challenge: Are you looking forward to slowing down on the blogging in May, or will you just miss it? I'm a bit of both . . .


-----The Golden Eagle

A-Z Blogging Challenge: X Chromosome

The X chromosome.
Public domain image.
SOURCE.

The X chromosome is one of two human sex-linked chromosomes, the other being the Y chromosome.

The X chromosome has around 155 million DNA base pairs, or 1000-2000 genes. 1,098 of those genes code for proteins and consist of around 5% of all the DNA in human cells. The X chromosome is larger and carries more genes than the Y chromosome, which means that if a gene on the X chromosome codes for a disease, that recessive trait will apear in any male children, since there is no dominate gene to counteract it. This characteristic of the X chromosome is visible in the fact only female cats can be calico, for its the females carry the allele for color and it can only code for one color at a time.

Females get two X chromosomes and males an X and a Y; since the normal chromosome count is 46 in total, females are denoted as 46,XX and males 46XY. In all cells other than egg cells, one of the two X chromosomes is inactivated (called Lyonization) except for a small area called the pseudoautosomal region. Many of the genes in the pseudoautosomal region are necessary for human development.

A graphic of triple X syndrome, with a male on the left and female on the right, by
Silver Spoon, CC-BY-SA-3.0. SOURCE.

Problems that can arise from changes along the X chromosome include microphthalmia (deletion of some of the genetic information on the chromosome; results in failure to create the enzyme holocytochrome c-type synthase, which in turn produces cytochrome-c, which in turn is involved in oxidative phosphorylation that allows mitochondria to create ATP), triple X syndrome (also known as 47,XXX and trisomy X; caused by having three X chromsomes), and Turner syndrome (also called 45,X, it is when only one normal X chromsome is present and the second of the pair is missing or changed; occasionally, only some cells are altered, called mosaicism).

A video about genetics, which explains the role of chromosomes and DNA:

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Sources:
http://biology.about.com/od/basicgenetics/a/aa110504a.htm
http://www.bio.miami.edu/dana/dox/calico.html
http://www.brighthub.com/science/genetics/articles/35283.aspx
http://ghr.nlm.nih.gov/chromosome/X
http://medical-dictionary.thefreedictionary.com/X+chromosome
http://www.medterms.com/script/main/art.asp?articlekey=6030
http://www.nlm.nih.gov/medlineplus/ency/article/002327.htm
http://www.nytimes.com/2007/05/01/science/01angi.html
http://www.thefreedictionary.com/X+chromosome
http://www.wisegeek.com/what-is-an-x-chromosome.htm

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And if you want information about the other chromosome, stop by tomorrow--I also explain why there was speculation humanity would go extinct because of the Y chromosome. Just in case that interests you . . .

-----The Golden Eagle