Welcome to The Visible Embryo

Home- - -History-- -Bibliography- -Pregnancy Timeline- --Prescription Drugs in Pregnancy- -- Pregnancy Calculator- --Female Reproductive System- News Alerts -Contact


Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

The Visible Embryo provides visual references for changes in fetal development throughout pregnancy and can be navigated via fetal development or maternal changes.

The National Institutes of Child Health and Human Development awarded Phase I and Phase II Small Business Innovative Research Grants to develop The Visible Embryo in 1993 as a first generation internet teaching tool consolidating human embryology teaching for first year medical students.

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.


WHO International Clinical Trials Registry Platform
The World Health Organization (WHO) has created a new Web site to help researchers, doctors and patients obtain reliable information on high-quality clinical trials. Now you can go to one website and search all registers to identify clinical trial research underway around the world!



Home

History

Bibliography

Pregnancy Timeline

Prescription Drug Effects on Pregnancy

Pregnancy Calculator

Female Reproductive System

Contact The Visible Embryo

News Archive
Disclaimer: The Visible Embryo web site is provided for your general information only. The information contained on this site should not be treated as a substitute for medical, legal or other professional advice. Neither is The Visible Embryo responsible or liable for the contents of any websites of third parties which are listed on this site.
Content protected under a Creative Commons License.

No dirivative works may be made or used for commercial purposes.

Return To Top Of Page
Pregnancy Timeline by SemestersFemale Reproductive SystemFertilizationThe Appearance of SomitesFirst TrimesterSecond TrimesterThird TrimesterFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory 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 HemispheresEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterDevelopmental Timeline
Click weeks 0 - 40 and follow fetal growth
Search artcles published since 2007

December 20, 2012--------News Archive Return to: News Alerts


Surprisingly, many mammals do not produce equal
numbers of male and female offspring.






WHO Child Growth Charts

       

Survival of the Females

It is well known that many mammals adjust the ratio of male and female young to the surrounding conditions at the time of conception – but now growth factors including insulin like growth factor (IGF)-1 has been shown to promote embryonic development by decreasing apoptosis and increasing cell proliferation

A recent study in the group of Christine Aurich at the University of Veterinary Medicine, Vienna has provided important information on how the survival of female embryos may be enhanced under conditions that would otherwise tend to favour the birth of males.

The work is published in the journal Theriogenology.

Because of the process involved in the formation of sperm cells, there should be an equal chance that a mammalian egg will be fertilized by “male” sperm, carrying a Y chromosome, as by a “female” sperm, carrying an X chromosome. The symmetry of the system ensures that roughly the same number of males and females are born, which is clearly helpful for the species’ long-term survival.

Surprisingly, though, many mammals do not produce equal numbers of male and female offspring.

The discrepancy could theoretically be explained by the differential efficiencies of male and female sperm (Y chromosomes are smaller than X chromosomes so perhaps male sperm can swim faster?) or by different rates of survival of male and female foetuses in the uterus. Indeed, it does seem as though male embryos are better able to survive under conditions of high energy intake. But why?


Jana Beckelmann in Christine Aurich’s laboratory at the
University of Veterinary Medicine, Vienna now presents
provocative evidence that a particular protein,
insulin-like growth factor-1 or IGF1, might be involved.

After examining about 30 embryos, Beckelmann noticed
that in early pregnancy (between eight and twelve days
after fertilization) the level of messenger RNA encoding
IGF1 was approximately twice as high in
female embryos as in male embryos.

The difference could relate to the fact that female embryos
have two X chromosomes, which together might produce
more factor required for the expression of the IGF1gene
than the single X chromosome in males can generate.

Beckelmann was also able to confirm that the IGF1
protein was present in the embryos, confirming that the
messenger RNA is actually being translated into protein.


IGF1 is known to have important functions in growth and to inhibit apoptosis, or programmed cell death. As IGF1 treatment of cattle embryos produced in vivo improves their survival, it is likely that the factor has positive effects on the development of the early embryo in the horse. So why should female embryos contain more of the factor than males?

Losses in early pregnancy are unusually high in the horse and it is believed that female embryos are especially prone to spontaneous abortion. Male embryos are known to be better able to survive under high glucose concentrations, so well-nourished mares preferentially give birth to male foals.


“We think the higher IGF1 concentrations in female
embryos might represent a mechanism ensuring the
survival of female embryos under conditions that
would otherwise strongly favour males.”

Jana Beckelmann

If this is so, the ratio of the sexes in horses
is the result of a subtle interplay between
environmental and internal factors,
including insulin-like growth factor-1.


The paper "Sex-dependent insulin like growth factor-1 expression in preattachment equine embryos" by Jana Beckelmann, Sven Budik, Magdalena Helmreich, Franziska Palm, Ingrid Walter and Christine Aurich in the journal "Theriogenology" is available online and will appear in print in the issue of January 1, 2013 (Volume 79, Issue 1, 1 January 2013, pp. 193-199).

Original article: http://www.vetmeduni.ac.at/en/research/research-output/press-releases/foals-sex/