On Monday, America's top court began hearing arguments in a case that reads like a science fiction novel: can companies patent human genes?

For almost three decades, the U.S. Patent and Trademark Office has been granting companies and researchers patents on human genes, but until now the legality of the practice has always had a bit of a question mark around it, even as the subject itself has fascinated scientists for over a century.

CBC News takes a look at the evolution of genetic science:

A Czech monk's pea plants

Starting in the mid-1850s, Czech monk Gregor Mendel tracked the hereditary patterns of more than 10,000 pea plants that he grew over eight years in a monastery garden. The so-called father of modern genetics, Mendel was the first to notice dominant and recessive genes when he observed how the offspring of purebred plants with two different characteristics did not blend the two, but displayed only one.

He found that each parent gives one gene to its offspring, and that one of those genes can be a trait that does not manifest itself physically.

Although he published his findings in 1865, they went largely unnoticed and not understood until the early 1900s.

From pus to DNA

In the late 1860s, Swiss biologist Friedrich Miescher, a man who would have become a priest if not for his father's disapproval, was the first to isolate DNA from cells and identify it as a distinct molecule.

Miescher researched white blood cells, which he extracted from pus found on bandages supplied by a nearby clinic. During his experiments, he isolated a new molecule from the cell's nucleus. Back then, the 25-year-old called it nuclein rather than today's term: nucleic acid, which is what the last two letters in DNA, deoxyribonucleic acid, stand for.

The double helix

In April 1953, the scientific journal Nature published a paper by James Watson and Francis Crick. "This structure has novel features which are of considerable biological interest," wrote Watson and Crick. The understated sentence signified that the two men — along with another pair of scientists, Maurice Wilkins and Rosalind Franklin — had cracked a mystery plaguing scientists at the time: what does DNA look like?

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The world's first clone of an adult animal, Dolly the sheep was born in 1996, but had to be euthanized six years later. (Reuters)

Franklin's now famous photograph 51 tipped off the pair. The photo showed a fuzzy X in the middle of a DNA molecule. Watson and Crick clued in to DNA's helical structure and posited DNA took the shape of a double helix, similar to what the railings of a spiral staircase looks like.

Watson and Crick also discovered DNA's base pairing system. In the 1940s, scientists knew DNA was made up of four bases: adenine, thymine, guanine and cytosine. However, Watson and Crick showed that adenine-thymine and guanine-cytosine pairings allowed for DNA's double helix structure.

The trio, minus Franklin, received a Nobel Prize in 1962. Franklin had died four years earlier, and the Nobel Prize can not be awarded posthumously.

Canada's stem cell legacy

In the 1900s, scientists were already discussing the idea of a self-renewing cell, but it took two Canadians to confirm the existence of stem cells.

Ernest McCulloch and James Till started out administering radiation to mice before giving the animals bone marrow transplants.

They shifted their focus after autopsies showed the mice had spleen nodules containing dividing cells — some specializing into red cells and some into white cells or platelets, which are the three main types of blood cells. These dividing cells were "directly proportional to the number of live marrow cells" the mice had been given, according to the Lasker Foundation, which awarded the men the prestigious Lasker prize for their work.

What they had discovered was that stem cells can self-renew and differentiate into specialized cells, setting the stage for today's stem-cell research into areas such as searching for a cure for Parkinson's disease to treating spinal cord injuries.

Cloning Dolly

On July 5, 1996, the world's most famous sheep was born. Dolly, named after country singer Dolly Parton, was the first mammal successfully cloned from a single adult cell (an udder cell planted in an egg and inserted in a surrogate mother). Scientists euthanized Dolly six years later because she suffered from a serious lung infection.

In 1952, scientists successfully cloned an animal for the first time, but the tadpole was cloned from embryonic cells rather than adult cells, like the kind from which Dolly was created, according to the human genome project's website. Since Dolly, scientists have cloned goats, cows, mice, pigs, cats, rabbits and a guar, which is a large species of wild cattle.

The human genome project

In 1990, an international group of scientists embarked on a 13-year project to identify all the genes in human DNA and "determine the sequences of the three billion chemical base pairs that make up human DNA," according to the project's website.

In 2003, two years earlier than anticipated — and on the 50th anniversary of the publication of Watson and Crick's double helix discovery— scientists declared the human genome project completed.

The achievement was compared to other scientific landmarks like the discovery of penicillin. The project's findings gave scientists a blueprint to human biological functions and susceptibility to illnesses.

Scientists made their findings publicly available, hoping it would help deepen the understanding of genetic causes for diseases and aid the development of therapies. Knowledge from the human genome project "can lead to revolutionary new ways to diagnose, treat and someday prevent the thousands of disorders that affect us."

With files from the Associated Press