Tag Archives: sperm

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.


The big. ass. egg.

15 Nov

Womanhood is powerful. If ever you seek a concrete image to illustrate this, look at a human egg flanked by sperm.

The first thing you will notice is that the egg is huge. Sperm cells swarm like tiny rockets around a super planet. Continue reading

The biological big bang

28 Oct

Baking soda and vinegar: Lots of fun.  Peanut butter and chocolate: Extremely delicious.  Egg and sperm: The most amazing pair in the universe!

They put on an awesome show.

How does 1 cell divide and grow to become a human being that is trillions of cells big?

Mitosis is the spark of life that starts from conception, or the merging of egg and sperm.  It is the most fundamental way in which we grow in our bodies, and the materials of mitosis come from, initially, the mother.

Kablooey! Read more…

Scrambled eggs, mutant sperm

4 Oct

MEIOSIS: A cell with 46 chromosomes becomes four sperm, each with 23 chromosomes. Shown here, the "Chromosome 1" pair (top left) gets duplicated, shuffled, and divided into sperm cells (bottom).

In other posts, we’ve discussed meiosis and mitosis, the two little cellular dances that need to be considered on the way to a basic understanding of genetics.

Meiosis affords genes the opportunity to recombine.  Mitosis affords genes the opportunity to replicate, and replication gives genes the opportunity to mutate.

Both processes are involved in the production of eggs and sperm, but eggs recombine more than sperm, and sperm replicate more than eggs.  Hence the title of this post, in which we will describe how sperm and eggs are made inside of the testicles and ovaries of two randomly chosen celebrities.


Bob Saget’s body will, over his lifetime, create billions of sperm.  Right now, inside of his testes, the sperm-making factory is running. (We invoke Bob Saget here as an example; we could have chosen any person with testicles.)

Inside of Bob Saget’s testicles are little tubes that are lined with spermatogonia, the germ cells that can divide and develop into sperm.  These cells proliferate through a process called mitosis, where one cell divides into two cells, each with the same set of chromosomes as the original. Continue reading

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!