Nettie Stevens discovered XY chromosomes — and then a man took credit for her work

Nettie Stevens is renowned for her revolutionary research on XY chromosomes, the link between genetics and sex determination. She was born 155 years ago today, and is remembered in the latest Google Doodle, despite it taking centuries for her work to be credited to her. Before Stevens’ findings, scientists had a completely different idea about how a person’s sex was determined.

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The Island Fox is a diminutive and docile fox unique to California’s Channel Islands. In fact, they are the only carnivore unique to California. They are broken up into six subspecies, living on and named after 6 of the 8 Channel Islands.

A new study has revealed that they are unique in another incredible way: they are nearly genetically identical to one another. A lack of genetic diversity can pose serious threats to survival, yet the Island Fox population has been recovering for the last few years (though they are still listed as ‘near threatened’). Read more about this trait and how it may affect the future of the foxes here.
Academies of Science finds GMOs not harmful to human health
Genetically engineered crops do not cause increases in cancer, obesity,autism or allergies, a new report says

Genetically engineered crops are safe for humans and animals to eat and have not caused increases in cancer, obesity, gastrointestinal illnesses, kidney disease, autism or allergies, an exhaustive report from the National Academies of Science released Tuesday found.

Work on the 388-page report began two years ago and was conducted by a committee of more than 50 scientists, researchers and agricultural and industry experts convened by the National Academies of Sciences, Engineering, and Medicine. It reviewed more than 900 studies and data covering the 20 years since genetically modified crops were first introduced.

Overall, genetically engineered (GE) crops saved farmers in the United States money but didn’t appear to increase crop yields. They have lowered pest populations in some areas, especially in the Midwest but increased the number of herbicide-resistant weeds in others. There’s also no evidence that GE crops have affected the population of monarch butterflies, the report said.

The review was thorough and systemic, assessing many of the issues that have been raised about genetically engineered crops over the years, said Gregory Jaffe, director of biotechnology at the non-profit watchdog group the Center for Science in the Public Interest in Washington D.C. The group was not involved in the report’s creation.

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Happy National DNA Day! Did you know the Human Genome Project was completed on April 23, 2003? 

To celebrate, here’s a short comic to teach you how to spot left handed and right handed DNA. Once you know how you can shame media outlets who didn’t bother to check their stock photos educate other people about DNA chirality!

Mendel’s Laws

1. the Law of Dominance
2. the Law of Segregation
3. the Law of Independent Assortment

The Law of Dominance 

In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. Offspring that are hybrid for a trait will have only the dominant trait in the phenotype.

  • Mendel crossed many different combinations of pea plants
  • When pure tall plants crossed with pure short plants, all the new pea plants (referred to as the F1 generation) were tall.  
  • Similarly, crossing pure yellow seeded pea plants and pure green seeded pea plants produced an F1 generation of all yellow seeded pea plants. 
  • Instead of creating medium height plants or yellowy-green seeds that might have been expected, one trait came out as dominant
  • Ie there is a gene that codes for height. One allele (form of the gene) codes tall and another short. In this case, the tall is dominant
  • The dominant is represented with a capital letter (eg T for tall) while the recessive is lower case (t)

The cross Mendel performed was

Parents (P):  TT x tt

where T = the dominant allele for tall stems
&  t = recessive allele for short stems

The punnet square looks like:

A plant that contains the dominant T will be tall, explaining why 100% of the plants he crossed came out tall.

The Law of Segregation

During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.  Alleles for a trait are then “recombined” at fertilization, producing the genotype for the traits of the offspring.

Now, Mendel decides to cross the offspring from the above experiment - all Tt

  • Two of the “F1” generation (tall) are crossed
  •  Would assume to get all tall again as tall is dominant
  • HOWEVER some come out short
  • “F2″ generation is about ¾ tall & ¼ short


  • Parent plants for this cross each have one tall factor that dominates the short factor & causes them to grow tall.
  • To get short plants from these parents, the tall & short factors must separate (allowing the possibility of 2 short factors coming together without a dominant tall) otherwise a plant with just short factors couldn’t be produced
  • The factors must SEGREGATE themselves somewhere between the production of sex cells & fertilization

Two hybrid parents, Tt x Tt.

The punnet square would look like this:

This splitting happens during meiosis.

The Law of Independent Assortment

Alleles for different traits are distributed to sex cells (& offspring) independently of one another.

  • Previously Mendel addressed one trait at a time.  
  • He noticed that different traits had no effect on each other, eg being tall didn’t automatically mean the plants had to have green pods
  • The different traits seem to be inherited INDEPENDENTLY.

The genotypes of our parent pea plants will be:

RrGg x RrGg where
"R” = dominant allele for round seeds
“r” = recessive allele for wrinkled seeds
“G” = dominant allele for green pods
“g” = recessive allele for yellow pods

The results from a dihybrid cross are always the same:

  • 9/16 boxes (offspring) show dominant phenotype for both traits (round & green), 
  • 3/16 show dominant phenotype for first trait & recessive for second (round & yellow) 
  • 3/16 show recessive phenotype for first trait & dominant form for second (wrinkled & green)
  • 1/16 show recessive form of both traits (wrinkled & yellow).


Sperm banks should get stricter about who gets to come inside them

Sperm donation is already strict business. There’s a battery of screening methods for genetic diseases that go down before you even get handed your cup. But those tests are still leagues behind what we’re technologically capable of providing in terms of preventing hereditary disease in the child. This needs to change and here’s how.

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The life of Dolly the sheep

20 years ago today - Dolly the sheep was born (5th July 1996) 

We take a look at the life of the world’s most famous sheep

Making Dolly

Dolly was part of a series of experiments at The Roslin Institute that were trying to develop a better method for producing genetically modified livestock. If successful, this would mean fewer animals would need to be used in future experiments.

Dolly was cloned from a cell taken from the mammary gland of a sheep, and an egg taken from a Scottish Blackface sheep.

She was born to her Scottish Blackface surrogate mom on 5th July 1996. 

Dolly’s white face was one of the first signs that she was a clone because if she was genetically related to her surrogate mother, she would have had a black face. 

Because Dolly’s DNA came from a mammary gland cell, she was named after the country singer Dolly Parton. 

Why was Dolly so important?

Dolly was important because she was the first mammal to be cloned from an adult cell. Her birth proved that specialised cells could be used to create an exact copy of the animal they came from.

Dolly’s life

Dolly was announced to the world on 22nd February 1997. Dolly captured the public’s imagination - no small feat for a sheep - and sparked a public debate about the possible benefits and dangers of cloning.

In the week that followed the announcement, The Roslin Institute received 3,000 phone calls from around the world.

Dolly spent her life at The Roslin Institute, and apart from the occasional media appearance, led a normal life. Over the years, Dolly had a total of six lambs with a ram called David. 

After Dolly gave birth to her last lambs in September 2000, it was discovered that she’d become infected by a virus called JSRV, which causes lung cancer in sheep. Other sheep at The Roslin Institute had also been infected with JSRV in the same outbreak.

Dolly continued to have a normal quality of life until February 2003, when she developed a cough. A CT scan showed tumours in her lungs, and the decision was made to euthanise Dolly rather than risk her suffering. Dolly was put to sleep on 14th February 2003, at the age of six.

What made Dolly so special is that she had been made from an adult cell, which no-one at the time thought was possible. This knowledge changed what scientists thought was possible and opened up a lot of possibilities in biology and medicine.

To find out more about the science behind Dolly the sheep, visit


Our DNA is 99.9% the same as the person sitting next to us.

Physicist Riccardo Sabatini recently demonstrated a printed version of your genetic code would fill 262,000 pages, or 175 big books.

Large amounts of genetic code are used for similar biological mechanisms that are the same across many species. Here’s other genetically similar species.

(Business Insider)
Memories Can Be Inherited, and Scientists May Have Just Figured out How
Our life experiences may be passed on to our children and our children's children - and now scientists report that they have discovered that this inheritance can be turned on or off.

Our life experiences may be passed on to our children and our children’s children - and now scientists report that they have discovered that this inheritance can be turned on or off. 


Epigenetics is the study of inherited changes in gene expression…changes that are inherited, but they are not inherent to our DNA. For instance, life experiences, which aren’t directly coded in human DNA, can actually be passed on to children. Studies have shown that survivors of traumatic events may have effects in subsequent generations.

The question, of course, is how are these genetic “memories” passed on?This is the question that a Tel Aviv University (TAU) was seeking to answer when they reportedly discovered the exact mechanism that makes it possible to turn the transference of environmental influences on or off.

(excerpt - click the link for the complete article)
This 2,500-year-old corpse could change history
A rare genome has been identified in an ancient body pulled from a sarcophagus on a site near ancient Carthage, in a discovery which could throw new light on the history of human movement. The DNA of the 2,500-year-old remains of the ‘Young Man of Byrsa’ , discovered in 1994 and believed to be that of a young male Phoenician, was sequenced by a team of scientists.

It’s Surprisingly Easy To Brew Something Like RNA In A Puddle 

One of the biggest mysteries in science is how you could get life in a place where it doesn’t already exist. Scientists have found some clues, though.

The latest is that Georgia Tech chemist Nicholas Hud was able to create something that looks a lot like RNA — a relative of DNA — using ingredients that would have been common on Earth when it was 4 billion years younger.

The study used two common chemicals left alone in what amounts to a mud puddle. The chemicals synced up and started forming that twisting ladder shape we think of when we picture DNA.

Scientists say this looks like a decent candidate for how simple organisms may have gotten started on Earth, and it wasn’t even all that hard.

Earlier studies have shown you can get some of the building blocks of life in the right situation, like extreme heat or lightning strikes. Some have even been found on asteroids.

The Georgia Tech study shows you don’t even need that much excitement. Swirling puddles could potentially have done the job.

By: Newsy Science.

Half of Western European men descended from one Bronze Age ‘king’

Half of Western European men are descended from one Bronze Age ‘king’ who sired a dynasty of elite nobles which spread throughout Europe, a new study has shown.

The monarch, who lived around 4,000 years ago, is likely to have been one of the earliest chieftains to take power in the continent.

He was part of a new order which emerged in Europe following the Stone Age, sweeping away the previous egalitarian Neolithic period and replacing it with hierarchical societies which were ruled by a powerful elite.

It is likely his power stemmed from advances in technology such as metal working and wheeled transport which enabled organised warfare for the first time.

Although it is not known who he was, or where he lived, scientists say he must have existed because of genetic variation in today’s European populations. Read more.