In your grandmother’s womb: The egg that made you.

29 Sep

The cell you came from was once inside of your mother’s fetus in her mother’s womb.

Although I was born in 1976, the egg that I came from was created in my grandmother’s womb– somewhere in Georgia, in 1946.

Want to calculate the vintage of the egg you came from?  Take your mother’s date of birth and subtract about 20 weeks.

That’s true because unlike males, who constantly generate sperm after they hit puberty, girls are born with their one and only lifetime supply of eggs.  Around the 20th week of gestation, a female fetus has developed a reproductive system, including 6 to 7 million eggs in her ovaries.

The matrilineal line looks much like a nested Russian doll.

The egg that created you was formed inside of your mother’s fetus while she was inside of your grandmother’s womb.

UPDATE: A few comments have pointed to a recent study in mice that suggests the possibility that a woman’s supply of eggs might be replenished. Questions remain about this controversial finding that scientists are working to understand, verify and replicate. We think it’s premature to revise the textbooks, but it’s exciting to consider new possibilities in science and to follow how they are validated or refuted by the scientific process. This finding, if true, could have implications for fertility treatment, so we’ll stay tuned!

Science of Pregnancy Week Two: Fertility

18 Apr

Your egg, preparing for debut

Girls are born with ~1-2 million eggs in their ovaries. In adulthood, a fraction of these eggs ripen. In a typical menstrual cycle, one egg is launched each month on a great lazy river ride. It’s released from the ovary, swept up in the tendrils of the fallopian tube, and ushered by a gentle tide toward the uterus.

When you had your period last week, your body flushed out an egg that was not fertilized during that adventure. But your body is already at work preparing the next contestant.

If you are trying to conceive, your most fertile period is in this window: the week leading up to, and including, ovulation.  Check an ovulation calendar to identify when you are most likely to become pregnant.

During this time, several hormones are working like greek goddesses in your system, bestowing vital gifts to prepare your egg for its journey: protective shield, snack bags, a safe landing zone— and plenty of sperm-grabber, just in case.



Meiosis Part Two: Two Halves

20 Dec

Plato looked at love as two half-beings coming together as one. Genetically, we ARE two half-beings fused together as one. Isn’t that rad?


The Improbability of You: Meiosis Part One

31 Jul

In this video, we talk about how improbable it is that you exist, the durability of genetic information across time, your relatedness to all living this on earth, and your uniqueness. These concepts will lay the foundation for explaining meiosis — the cellular dance that makes you a mosaic of your ancestors who is different from everyone else, even your siblings.

Having sex to become pregnant: Why it is necessary?

15 Aug

The gorgeous plumes of a peacock are a classic example of a trait that emerged solely for sex appeal.

“Some are fancy on the outside.  Some are fancy on the inside.  Everybody’s fancy.  Everybody’s fine.  Your body’s fancy, and so is mine.”  –Fred Rogers (♫ listen here)

“Some mollusks (not many) can have children merely by sitting around and thinking about it.”   — E.B. White, Is Sex Really Necessary?

As it turns out, snail sex (a snail is a type of mollusk) is really far out:  Some can self-fertilize, some stab their mates during foreplay with harpoon-like “love darts,” and most snails have two sex organs, so they can do it both ways at the same time.  As E. B. White observed, “mollusks are infinitely varied in their loves, their hates and their predilections.”  See snails doing it!

The Science of Pregnancy Timeline– Week 0: Menstruation

15 Jun

Note: Because it can be hard to pinpoint exactly when a sperm and egg have merged, it is customary for midwives and doctors to start pregnancy calendars using the date of the mother’s last menstrual period, placing fertilization at “pregnancy week 2.”  To make this timeline consistent with the ones used for health visits (and other great timelines you may be reading), we are starting this one at “Week 0: Menstruation.”

The lining of the uterus– replaced monthly– is made to create a plush home for a fertilized egg.

The inner lining of the uterus is a big, red, comfy couch.

Its plushness is in place to welcome a fertilized egg to the dark, gentle world it will inhabit during nine months of growth. When no guest arrives, the luxurious couch goes out to make room for the next.

Menstruation is the end of one cycle and the beginning of the next. A signal goes out to the ovaries to begin preparing a new egg for release, two weeks later, into the fertile zone of the fallopian tubes.

An egg on this journey has already been through epic travels; it originally developed within your ovaries when you were just a fetus inside your mother’s uterus!

Each egg itself is a universe. What other thing in the entire world is so small and gives rise to something as large, beautiful, complex and long-lived as a human being? The egg’s capacity for creation precedes us by millennia and continues on in every species on the planet, in the annual bloomings of spring and the monthly cycles of women everywhere.

At the time of ovulation (two weeks before menstruation), the egg is at the edge of the island of the ovary. Hormones, a little like weather patterns, churn the seas around the ovaries until the egg breaks loose. This package is transferred directly to the superhighway of the fallopian tubes, where a journey of 3 to 4 inches will take several days. This is when fertilization may take place.

Typically, this journey toward the uterus is pretty solitary for the egg. It might hit viruses or bacteria, depending on the mother’s health. It could hit a road block if the mother’s had her tubes tied. And it could end up in a town of Hell’s Angels, and that’s the guy you just slept with.

If  fertilization happens, the egg will plant itself in the wall of the uterus. This big couch is also like the deep, rich, dark soil that you would find on the forest floor, where almost anything can grow.

If the egg is not fertilized within a day or two, it simply dissolves back into all that luscious warmth. Menstruation happens. And the cycle begins anew.

What’s next

Science of Pregnancy Timeline: Week 2 

Related posts

The Big. Ass. Egg.

About this timeline: Genedoe is an educational blog that aims to enhance the public's understanding of genetics– a topic that can inspire us to be healthier, to fathom the diversity and connectedness of living things on the planet, and to explore the comedies and tragedies that befall the human body.  The "Science of Pregnancy Timeline" is a 40-week calendar that we hope parents will read in conjunction with their nine months of expecting. (We will occasionally address 'you' with the assumption that you are a pregnant woman; we beg your pardon if this does not apply, and welcome you to our blog, where genetics is for everyone.) Thank you for your comments and your partnership in plumbing the depths and the wonders of pregnancy!

Pregnancy: Why do I feel crappy all the time?

1 Jun

Go look at a construction site. It’s a mess!

Even while things may appear normal on the outside, the same kind of heavy lifting and huge maneuvering is going on inside of the body.

The body is re-creating itself! 

Take, for example, the widening of the hips. Who is telling a mother’s body to prepare in this way, like a ball player slathering a glove with oil before a game? What’s going on at the mechanical level?

There’s a biochemical tool box that the body has to build structures, harden and soften them, and tear things down.

Those are the mother’s genes getting switched on, possibly for the first time. They’re working in response to signals that are being pumped out by the brain, the placenta, and even the baby’s brain. They give the body instructions for creating the tools it needs: The proteins that carry out all kinds of tasks in the uterus and throughout the mom’s body, including the hormones notorious for making us sleepy, nauseous, or grouchy.

If you were the size of a cell, you would look around at the enormous construction site of your body and be awed by the wrecking balls, delivery trucks, and bulldozers at work.

The body needs to rest and the brain needs to be patient and not hyper-vigilant wondering, “Is that gas, or cancer?” The attitude and approach of a mother is so important while the body is doing this work. It’s no cure, but it helps to know that it’s completely reasonable to feel exhausted or worse.


Miscarriage happens for a lot of really good reasons.

29 May

Loss is loss. And grief about loss is real.

But when miscarriage happens, it’s usually for a very good reason.

In the first weeks after conception, the genome is trying itself out.

“Can I make organs? If not, I am going to have a hard time on this planet. Let’s try again.”

Every baby that is born represents a spectacular cellular success. A cell that can magic itself into becoming a living being has to accomplish an elaborate trick; as we’ve pointed out before, making organs alone is like getting a Boeing 747 off the ground.

Life is rare and precious, but the possibility of life forming  is also astronomical. It’s why we have so many sperm and so many eggs. The whole system is set up to make life work. And that’s why they made sex fun.

So losing an embryo can be an opportunity to try again, and not a sign of something that is systematically wrong.

There’s a million ways that we form as snowflakes.

There’s a time to go at it again and have some more fun with it.

Are Genetics Blogs Legit?

13 Apr
In this blog we have told you stories about the foreplay of snails and the uterus of your granny.  Genetics is an incredible topic!  Which raises the question: Do you believe what we say here?
An article in Public Health Genomics this month took a look at genetics blogs (that’s us!!) and their various indicators of credibility.
Their findings: Most of the blogs they sampled disclosed authors’ full names (81%) and biographical information (67%).
Many blog authors reported having genetics (67%) or life science expertise (59%).
Only 7% of blogs were affiliated with educational or medical institutions.
Bloggers with life science expertise, who focus on ancestry, and post more frequently, they say, tend to be more influential.
These data tell GeneDoe something GeneDoe already know… We should post more frequently! And we will.
If you’ve come upon this post, please leave a comment:
We’d like to know what genetics blogs you read, if any, AND, what topics interest you. Maybe you’ve got a question that we can answer
Thanks for visiting us,
(GeneDoe, by the way, is co-authored by a writer with no genetics training and a geneticist who explains everything. We are Tevah Platt and Sharon Kardia, and we are affiliated with the University of Michigan’s School of Public Health and its Life Sciences and Society program. Click “about us” for more info.)

3 Bananas Long: A Genetics Song

15 Feb

Enjoy this genetics song written for our young Willa.

GeneDoe Hiatus

9 Nov

Due to genetics-related circumstances– the birth of baby Willa on Oct. 23– we will be taking a short hiatus from posting to GeneDoe.  Browse through our older posts and return for new entries before the new year.

In the meantime, take a look at Willa’s karyotype— and check out her phenotype!  What a cutie.



Willa's karyotype

Body building: step one

26 Aug

All animals begin as a ball of cells and emerge as amazing sculptures.

The body-building process begins with gastrulation:  In most cases, an indentation in the cell ball produces an opening that will eventually become the anus.  Cells migrate to form the three basic layers of the body, and they establish the primary axes that determine the right/left and front/back sides of the animal.  Once they’ve been organized like little subgroups at a conference, interactions among appropriate cells initiate the process of organ creation.

In this video we can actually watch the gastrulation process unfolding in the blastula (cell ball) that will become a little white frog.

Nurture begins in the womb

25 Aug
Epigenetics is the study of the chemical reactions that govern which genes get turned on or off. Wikipedia image credited to the National Institutes of Health (NIH).

Am I hungry? Have I just gotten sloshed? Am I in outer space?

All of these factors affect how I am feeling, and less obviously, how my genes are functioning.

If I am a pregnant lady, factors like these become critical because they impact the activation and silencing of genes that coordinate the delicate orchestration of my baby’s development.

Remember, genes are the same in all of our cells, but our cells and body parts look and behave differently because certain genes within them are switched on or off. And in order for the cells of a developing embryo to emerge is a person, genes need to be switched on and off at just the right moment.

What’s controlling these switches? It’s not the genes themselves. Epigenetic signals –(click this for great videos and articles on epigenetics from the University of Utah’s Genetic Science Learning Center) –are the conductors that cue genes in and out at just the right time. They change in function of what we eat, smoke, breathe and drink. _Read on