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Genetically predisposed circadian rhythm and time of death
Living creatures adjust their biological activities according to the local environmental factors. Thanks to those factors, animals could determine perfect time to eat, sleep, mate, migrate… Pattern of behavior is changing during the day, week or season. Day light is the most important factor that affects biological activity on a daily basis. Established rhythm of behavior is known as circadian rhythm and it is driven by circadian clock. This “clock” is endogenous and it is unique for each individual. People are usually classified as early birds or night owls. No matter which category you belong, latest discoveries reveal genetic background behind this phenomenon.

Suprachiasmatic nucleus is located in the hypothalamus. This organ receives information about day light from retina via tight neuronal connection (retinohypothalamic track). After day light information is processed, it will be sent to a pineal gland that is responsible for melatonin production. Melatonin is hormone essential for sleeping. Level of melatonin is highest in the night and lowest in the morning. This hormone is important marker for sleep-wake rhythm screening. Electric light in the evening can affect normal circadian rhythm by delaying sleeping phase. Every man has its own rhythm and not all people demand 7 hours of sleep to achieve body refreshment and prepare themselves for the up-coming daily activities. Sleep duration is dropping down with age and old people usually sleep just few hours per day.

Scientists from the Neurological department of the University of Toronto investigated sleeping patterns of older people and discovered connection between genotypes and circadian rhythm. It was shown that genotype could even predispose time of person’s death. Original idea of the study was to investigate potential triggers of Alzheimer’s and Parkinson’s disease in the certain age group. Since all patients were genotyped, Dr. Lim (leader of the project) decided to expand study goals and explore connection between sleep-wake patterns and specific genotypes. This was large study conducted on the 1200 individuals having 65 years or more. It lasted over a decade and participants donated their brains for further post mortem analysis. Period 1 and Period 2 genes are well known genes, recognized as important for light entrapment and establishment of normal sleep-wake rhythm. When those genes were altered in experiment with mice, animals couldn’t respond normally to the light changes and sleeping pattern was disrupted. In this study, single nucleotide, located near Period 1 gene, showed slight alteration that correlated with differences in sleep-wake pattern observed between study participants. Adenosine (nucleotide) was found in 60% participants at the mention location while guanine was found in the remaining 40% cases. Since DNA is double helix, chances that adenine will be seen in other chain was 36% (resulting in A-A genotype), chances that guanine will be seen at exact same spot in the other chain was 16% (resulting in G-G genotype) and finally there was 48% chance of having a mixture of adenine and guanine (resulting in A-G genotype). Three described genotypes showed different sleeping patterns. A-A genotype wakes up one hour before G-G genotype and waking time of the A-G is in the middle of the A-A and G-G genotypes. Expression of the Period 1 gene is lower in the individual with G-G genotype during the day when the gene is normally expressed. Since every biological activity is driven by circadian rhythm, Dr. Lim wanted to discover if genes affecting sleep-wake pattern could also affect the time of death. Patients enrolled in the study participated over 15 years and a lot of them died during the study due to natural causes. Closer analysis of brain tissue and genetic material showed direct correlation between most likely time of a death (part of a day) and genotype. Participants with A-A and A-G genotypes passed away around 11 o’clock in the morning and participants with G-G genotype passed away around 6 o’clock in the evening. For the first time, one study showed that circadian rhythm could affect not just the time people will wake up or go to sleep, but the time when they will die.

Further experiments and even more information on this subject would be helpful for people working in shifts, changing time-zone often (and dealing with jet lag) or having trouble with daily tasks organization.
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What is that A-A genotype ?,usually A pairs with G nucleotide..Can any one explain that

Then how it was proved that Individuals with A-A genotype dead in morning and G-G in evening?

Like to read little detail..plz can u help me with the link!
Bv ram- I'm student for all those who teaches me
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(12-01-2012, 08:50 PM)bvs science freak Wrote: What is that A-A genotype ?,usually A pairs with G nucleotide..Can any one explain that

A-A genotype doesn't mean bond between two adenosine nucleotides. It means that two adenosine nucleotides in the single DNA chain are placed next to each other. Same is with G-G genotype. They form complementary bonds with their usual nucleotide pairs (A-T, and G-C) in other chain.

Then how it was proved that Individuals with A-A genotype dead in morning and G-G in evening?

Simply, by calculating (statistically) the number of people having one or another type of genotypes and the time of death - they concluded that people with A-A genotype have more chance to die in the morning, and G-G in the evening.

Like to read little detail..plz can u help me with the link!
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