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Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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Pregnancy Timeline by SemestersLungs begin to produce surfactantImmune system beginningHead may position into pelvisFull TermPeriod of rapid brain growthWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madeImmune system beginningBrain convolutions beginBrain convolutions beginFetal liver is producing blood cellsSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
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Home | Pregnancy Timeline | News Alerts |News Archive Feb 27, 2015

A diagram of meiosis from Wikipedia.

 






 

 

Why some older mothers' babies have birth defects

Researchers have found a possible clue to why older mothers face a higher risk for having babies born with conditions such as Down syndrome — it's in the numbers.

A study shows that the normal process by which a parent's chromosomes are shuffled before being passed on to their eggs and sperm, appears to be less regulated in older moms. Data was collected from more than 4,000 families through a collaboration with the direct-to-consumer genetic testing company 23andMe, Inc., and published online in Nature Communications.


The research focused on meiosis, cell division in which each cell containing 46 chromosomes — made up of 23 pairs — separates to become sperm or egg. Each sperm and egg contains only 23 chromosomes, one from each of the initial 23 chromosome pairs. Before the chromosomes separate, the pairs exchange genetic material with each other — a chromosomal shuffling process known as recombination.


Recombination is vital to any species' genetic diversity. It ensures that sperm or eggs will have unique combinations of genetic traits. However, chromosome failure at the time of recombination can introduce errors such as aneuploidy (an abnormal chromosome number in either eggs or sperm) or large chromosome rearrangements. This is the first study to reveal that the spacing between chromosome recombination events on the same DNA strand become less constrained as women age.

"It's been known for many years that the rate of recombination varies across the genome, but less is known about how the rate of recombination changes with parental age," said study leader Adam Auton, Ph.D., assistant professor of genetics and of epidemiology & population health at Einstein.

The Einstein study involved genetic data gathered from more than 4,200 families (each with at least two children). Researchers closely examined episodes of recombination passed from parent to child. Examined were more than 645,000 recombination events amongst all 4,200+ families.*


Research confirmed that the number of recombination events transmitted from mother to child increased with maternal age. Additionally, they discovered that more recombination events occur in close proximity to each other in older mothers. By contrast, no such age-related effects were observed in fathers.


"We know there are cellular processes that tightly regulate the process of recombination," said Dr. Auton. "So the greater rate of recombination we observed in the chromosomes of older mothers could imply that this tight regulation becomes weaker with age. Basically, recombination appears to be a more dynamic process than we previously appreciated."


Researchers note that their findings have no clinical application as yet.


"Our study adds to the understanding of the basic biology of meiosis and how recombination shapes the evolution of the human species," said Dr. Auton. "In the long run, it may help us understand how aneuploidy or certain types of genetic mutation can occur through failures in recombination."

Abstract
Recombination plays a fundamental role in meiosis, ensuring the proper segregation of chromosomes and contributing to genetic diversity by generating novel combinations of alleles. Here, we use data derived from direct-to-consumer genetic testing to investigate patterns of recombination in over 4,200 families. Our analysis reveals a number of sex differences in the distribution of recombination. We find the fraction of male events occurring within hotspots to be 4.6% higher than for females. We confirm that the recombination rate increases with maternal age, while hotspot usage decreases, with no such effects observed in males. Finally, we show that the placement of female recombination events appears to become increasingly deregulated with maternal age, with an increasing fraction of events observed within closer proximity to each other than would be expected under simple models of crossover interference.

*Data was contributed by 23andMe customers who provided informed consent to take part in this research under a protocol approved by the AAHRPP-accredited institutional review board, Ethical and Independent Review Services.

The paper is titled "Escape from crossover interference increases with maternal age." The other authors are: Christopher L. Campbell, a Ph.D. student at Einstein; Nicholas A. Furlotte, Nick Eriksson, and David Hinds, all affiliated with 23andMe.

Nicholas A. Furlotte and David Hinds are current 23andMe employees and Nick Eriksson is a former 23andMe employee; all three have private equity interest in the company. The remaining authors declare no competing financial interests.

This study was supported in part by Albert Einstein College of Medicine, and by grants from the National Institutes of Health to Einstein (T32-GM007491) and 23andMe (2R44HG006981-02).

About Albert Einstein College of Medicine of Yeshiva University
Albert Einstein College of Medicine of Yeshiva University is one of the nation's premier centers for research, medical education and clinical investigation. During the 2013-2014 academic year, Einstein is home to 743 M.D. students, 275 Ph.D. students, 103 students in the combined M.D./Ph.D. program, and 313 postdoctoral research fellows. The College of Medicine has more than 2,000 full-time faculty members located on the main campus and at its clinical affiliates. In 2013, Einstein received more than $150 million in awards from the National Institutes of Health (NIH). This includes the funding of major research centers at Einstein in aging, intellectual development disorders, diabetes, cancer, clinical and translational research, liver disease, and AIDS. Other areas where the College of Medicine is concentrating its efforts include developmental brain research, neuroscience, cardiac disease, and initiatives to reduce and eliminate ethnic and racial health disparities. Its partnership with Montefiore Medical Center, the University Hospital and academic medical center for Einstein, advances clinical and translational research to accelerate the pace at which new discoveries become the treatments and therapies that benefit patients. Through its extensive affiliation network involving Montefiore, Jacobi Medical Center -- Einstein's founding hospital, and three other hospital systems in the Bronx, Brooklyn and on Long Island, Einstein runs one of the largest residency and fellowship training programs in the medical and dental professions in the United States. For more information, please visit www.einstein.yu.edu, read our blog, follow us on Twitter, like us on Facebook, and view us on YouTube.


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