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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.

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.)

Cheat Sheet: Dominance

25 Apr

The term “dominant” refers to the relationship between the two versions of a gene (more accurately, alleles) we inherit from each parent for the same trait.

For example, we all have two alleles that determine thumb-shape, one from mom, one from dad.  As it happens, we only need one of these alleles to code for straight thumbs in order to be born with straight thumbs.  Therefore this trait is said to be dominant, and the alternative, curvy thumbs, is said to be “recessive.”

It’s common to abbreviate dominant traits with a capital letter, and recessive ones in lower case.  For example, S=straight thumbs, and  c=curvy thumbs.  In this example, the combinations SS or Sc would give a person straight thumbs.  Only cc would result in “hitchhiker’s thumb,” the recessive trait where the thumbs curve backward in the upright, “thumbs up” position.

Ben Stiller has hitchhiker’s thumb, so he must have “curvy” thumb-shape alleles from both parents (cc).

Note that Anne Meara and Jerry Stiller could actually have straight thumbs and yet be carriers who were capable of passing along the “c” trait to Ben, if the alleles they got from their parents were, in both cases, S and c.  In this scenario, Ben Stiller would have had a 1 in 4 chance of inheriting the cc combination from his parents.

The “father of genetics” Gregor Mendel was the first to describe dominance when his experiments with pea plants showed pretty consistently that recessive traits like short, green or wrinkled appeared 1 in 4 times among the offspring of cross-bred plants.

Weekly reading: Your Inner Fish

16 Mar

“Carl Sagan once famously said that looking at the stars is like looking back in time.  The stars’ light began the journey to our eyes eons ago, long before our world was formed.  I like to think that looking at humans is much like peering at the stars.  If you know how to look, our body becomes a time capsule that, when opened, tells of critical moments in the history of our planet and of a distant past in ancient oceans, streams and forests.  Changes in the ancient atmosphere are reflected in the molecules that allow our cells to cooperate to make bodies.  The environment of ancient streams shaped the basic anatomy of our limbs.  Our color vision and sense of smell has been molded by life in ancient forests and plains.  And the list goes on.  This history is our inheritance, one that affects our lives today and will do so in the future.”

The overarching story of Your Inner Fish is that of descent with modification.  We are modified descendents of our parents, as were they, as were their ancestors, back to the origin of life.

Neil Shubin, the paleontologist and anatomy professor who co-discovered a significant fossilized “intermediate” between fish and land-dweller, tells this story with humor and grace.  Anecdotes about particular scientists and their historic experiments infuse the whole book with a tone of enthusiastic discovery.

At first glance, parts of our bodies seem to make no sense at all.  Looking at the winding nerves in our heads, or at the circuitous route that sperm takes from scrotum to penis, our bizarre plumbing and circuitry calls to mind the wiring of an old building with new innovations added on or wound around defunct or outdated structures.  That’s exactly because the human body, 3.5 billion years in the making, was built in just that way. 

For example, Shubin tells, us, 3 percent of our entire genome is devoted to genes for detecting various odors, many of which are useless to us but may have been critical to our mammal ancestors’ survival.

Hiccups irk us, but this likely remnant from our amphibious past allows tadpoles to pump water without flooding their lungs.

Shubin tells stories about particular genes—including Sonic hedgehog that is crucial in the development of limbs, or Hox genes that control the organization of the body—which function similarly across various species, from humans to fruit flies, mice to sharks.  Various mad, Frankensteinish experiments have shown amazing results from the swapping of genes among them.

“The best road maps to human bodies lie in the bodies of other animals,” writes Shubin.  “…We are not separate from the rest of the living world; we are part of it down to our bones [and] even our genes.”

Weekly Reading: It Ain’t Necessarily So

18 Nov

Richard Lewontin’s “It Ain’t Necessarily So: The Dream of the Human Genome and Other Illusions,” is an erudite collection of essays for readers interested in the recent politics and the intellectual history of genetic ideas. Continue reading

Weekly reading: The Ancestor’s Tale

27 Oct

WE– you and I– literally share a common ancestor with this unworldly creature!  And for that matter with all other life on planet Earth.

“The ravishingly beautiful Cestum veneris is one of those rare animals whose English and Latin names mean exactly the same thing, Venus’s girdle, and no wonder: the body is a long, shimmering, ethereally beautiful ribbon, too good for a goddess.” –Richard Dawkins  (Video from YouTube user quixoticknight used with permission.)

In The Ancestor’s Tale (Houghton Mifflin, 2004), Richard Dawkins guides the reader on a “pilgrimage” backward in time toward the common ancestor of all living things, which lived more than 3 billion years ago.

Tracing the evolutionary thread of humankind, the author describes 40 “rendezvous points” where humans come to share ancestors with distant cousins, from chimpanzees to eubacteria. Continue reading

What is a gene?

20 Oct

Courtesy of the U.S. Department of Energy Genome Programs:


When we talk about our genes, we are talking about the packages of biological information that we inherit from our parents, and less directly, from our millions of ancestors.

According to the researchers who mapped the human genome, a person has about 20 to 25,000 genes.

Our genes are made of DNA (deoxyribonucleic acid) and they live on thread-like strands called chromosomes at the center (the nucleus) of almost all of the trillions of cells in our bodies.

 We have 46 chromosomes– 23 from mom, 23 from dad.  Each set (mom’s and dad’s) contain only slightly different versions of the same genes.  Technically, each version is called an allele (pronounced uh-LEEL).

 Our chromosomes are like 23 cookbooks (two editions of each) and our genes are like recipes.  Our bodies read the recipes in order to cook up the amino acids that create proteins.  Proteins help our bodies form, grow, heal, move and function.

Cheat Sheets: Transcription and translation

19 Oct

 Genes are instructions for building proteins.

Some proteins are like bricks and mortar, used to build wild, slim features in nerve cells, for example, or to endow muscle cells with tight-knit, fibrous strength.

Some genes code for the proteins that make cells work.  These proteins are like machines, and thousands of different kinds of machines operate in any given cell.  So, if we pile it all up, people are made of trillions of cells and bazillions of proteins that were made off the same genomic recipe book.

Before they build proteins, machines inside of cells must find out how to build them by reading the DNA code of a gene and copying out its instructions.   This process is called transcription. Little factories inside of the cell called ribosomes then read and “translate” the code, making amino acids and linking them together into proteins.

It’s just like any other manufacturing business and process.  First, the business has to have the detailed specs (the genetic code) of what it is going to build (the proteins).  Second, copies of those specs (messenger RNA, or mRNA) get sent out to to all the places within the business that can make it.  Third, someone (like the ribosome) has to read the specs (mRNA) and pull the raw materials together (amino acids) in just the right way and with just the right glue (chemical bonds) to build it.  Finally, the finished product travels out to other businesses to be used (like muscle cells need lots of glucose-6-phosphate dehydrogenase, or G6PD, to break down sugar into raw engergy to power our legs.)

Above, a clip from the PBS production “DNA: The Secret of Life,” credited on Youtube: A Windfall Films Production for Thirteen/WNET New York in association with Channel Four. © 2003 Educational Broadcasting Corporation.

Click here to see all “Cheat Sheet” index cards covering the basics of genetics.

Cheat sheet: Meiosis and mitosis

1 Oct

Mitosis occurs so that dying cells can refresh life by dividing– allowing living things to grow and to stay alive.  Chromosomes are duplicated just before the cell splits.

Meiosis occurs so that sperm and egg cells each contain 23 chromosomes– instead of the 46 that show up everywhere else in the body.

Double click the photos to blow them up.

Read other “cheat sheet” index cards covering the basics of genetics.

Cheat Sheet: Genes, Chromosomes and DNA

25 Sep

Nature is the type of cook who is lost without her recipes. Chromosomes are cookbooks, and we have two editions of each.  The recipes are genes.

When we talk about our genes, we are talking about the packages of biological information that we inherit from our parents, and less directly, from our millions of ancestors.

According to the researchers who mapped the human genome, a person has about 20 to 25,000 genes.

Our genes are made up of DNA (deoxyribonucleic acid) strung together by the millions to make thread-like strands called chromosomes at the center (nucleus) of almost all of the trillions of cells in our bodies.

We have 46 chromosomes–23 from mom, 23 from dad.  Each set (mom’s and dad’s) contains only slightly different versions of the same genes.  Technically, each version is called an allele (pronounced uh-LEEL).

Our bodies read our genetic “recipes” in order to cook up amino acids that are the building blocks of proteins.  Proteins, in turn, help our bodies to form, grow, heal, move and function.

Explore the “Cheat Sheets” category to read index cards covering the basics of genetics.

Weekly reading: The Tentative Pregnancy

22 Sep

Barbara Katz Rothman’s The Tentative Pregnancy: How Amniocentesis Changes the Experience of Motherhood is about women’s experiences with prenatal diagnosis.

Published in 1986 (with a new introduction and appendices in the 1993 edition), this work was an early exploration of the ways in which the technology of amniocentesis alters women’s experience of pregnancy.  “The possibility of a bad diagnosis,” Rothman writes, “casts its shadow over the early months and the flow of time in pregnancy itself is changed with mid-pregnancy diagnosis.  Most important, the mother’s developing relationship with her fetus is affected by the new technology of reproduction.”

The author bases the work on interviews with mothers, recipients of genetic counseling and genetic counselors.

Topics include the scope and ambiguity of prenatal diagnoses; the risks and benefits of amniocentesis, and its emotional consequences.  The author includes a practical appendix, “Guidelines for Personal Decision-Making,” directed to women who are currently pregnant.