Ikigai Daily
Menu
WonderGenome evolution fact

Bread wheat carries six sets of chromosomes, two from each of three wild ancestral grasses. Organisms with more than two complete sets of chromosomes are called polyploid, and they are common among plants.

Polyploidy

EvolutionBiologyScience

The story behind the card

Most animals, including humans, have two sets of chromosomes, one from each parent. Wheat gained its extra sets in two steps. Long before farming, two wild grasses, Triticum urartu and a relative of Aegilops speltoides, crossed to produce wild emmer, with four sets. After farming began in the Near East, cultivated emmer crossed with a third wild grass, Aegilops tauschii, adding two more sets and creating bread wheat. The oldest known bread wheat, identified from its DNA, comes from Çatalhöyük in Turkey and dates to about 6400 to 6200 BC. Extra gene copies can take on new roles, one reason polyploid crops are often large and hardy. Potatoes, cotton, Arabica coffee and cultivated strawberries are polyploid too.

Türkçe oku
Ekmeklik buğdayda altı kromozom takımı bulunur: üç ayrı yabani atadan ikişer takım. İkiden fazla tam kromozom takımı taşıyan canlılara poliploit denir; bitkilerde bu durum oldukça yaygındır.

İnsan da dahil hayvanların çoğunda, biri anneden biri babadan gelen iki kromozom takımı bulunur. Buğday fazladan takımlarını iki adımda kazandı. Tarımdan çok önce iki yabani ot, Triticum urartu ile Aegilops speltoides'in bir akrabası, doğada melezleşti ve dört takımlı yabani gernik buğdayı ortaya çıktı. Yakın Doğu'da tarım başladıktan sonra, ekilen gernik buğdayı üçüncü bir yabani otla, Aegilops tauschii ile melezleşti; iki takım daha eklendi ve ekmeklik buğday doğdu. DNA'sı incelenerek belirlenen en eski ekmeklik buğday, Türkiye'deki Çatalhöyük'ten çıktı ve MÖ 6400-6200 yıllarına tarihleniyor. Fazladan gen kopyaları yeni işler üstlenebilir; poliploit bitkilerin çoğu zaman iri ve dayanıklı olmasının bir nedeni budur. Patates, pamuk, Arabica kahvesi ve bahçe çileği de poliploittir.

Sources and further reading

Background reading: Polyploidy
Get the mobile appAbout our cards

Related cards

These cards share a subject or reading mode with the card above.

WonderEvolution

In industrial Britain, the dark form of the peppered moth, first recorded in Manchester in 1848, became common where soot blackened the trees and hid it from birds. When the air was cleaned up in the twentieth century, the pale form returned.

The peppered moth became a textbook example of natural selection. By the 1890s nearly all peppered moths around Manchester were dark. In the 1950s Bernard Kettlewell's field experiments suggested that birds ate more of the moths that stood out against the bark, though critics later questioned his methods. After clean-air laws such as the UK's Clean Air Act of 1956 cut soot, the dark form became rare again. The geneticist Michael Majerus answered the critics with a six-year experiment in Cambridge involving 4,864 moths; published after his death, in 2012, it confirmed that birds took more of the conspicuous moths. In 2016 scientists traced the dark colour to a piece of mobile DNA inserted into a gene called cortex around 1819.

Peppered moth evolutionRead card
WonderEvolution

Convergent evolution happens when unrelated organisms independently evolve similar traits, such as streamlined bodies in sharks, dolphins and extinct ichthyosaurs.

Sharks are fish, dolphins are mammals and ichthyosaurs were marine reptiles, yet all three evolved a similar streamlined, fin-driven body built for fast swimming. The same pattern shows up elsewhere: camera-like eyes, with a lens that focuses light onto a retina, evolved independently in both vertebrates and octopuses, and the extinct Australian thylacine looked strikingly like a wolf despite being a marsupial with no close relation to dogs. Convergent evolution does not mean life is aiming for a fixed set of designs. Natural selection simply favours whatever body plan works best under a given set of physical pressures, so unrelated lineages can arrive at strikingly similar answers.

Convergent evolutionRead card
WonderEvolution

Maize, sugarcane and sorghum grow well in heat and strong sun partly because they use C4 photosynthesis, a way of concentrating carbon dioxide inside the leaf. This method has evolved independently more than 60 times in different groups of plants.

Most plants use C3 photosynthesis, which relies on an enzyme called RuBisCO to capture carbon dioxide. In heat and drought, plants close the pores in their leaves to save water, carbon dioxide inside runs low, and RuBisCO grabs oxygen instead, wasting energy in a process called photorespiration. C4 plants first trap carbon dioxide in their outer leaf cells as a compound with four carbon atoms, which gives the pathway its name, then carry it to inner cells where RuBisCO works and release it there, so the enzyme is surrounded by carbon dioxide. With more than 60 separate origins, it is one of the most often repeated adaptations in plant evolution. Scientists are now trying to engineer the trait into rice.

C4 photosynthesisRead card
WonderOcean

When attacked, hagfish release mucus and microscopic protein threads that expand through seawater into extraordinary volumes of defensive slime.

Hagfish are eel-shaped, jawless fish that live on the seafloor. More than 70 species are known, and fossils about 300 million years old already look much like them. They often feed by burrowing into the carcasses of dead fish and whales. Their slime comes from glands along the body, which release mucus and tightly coiled protein threads. In seawater the threads unravel in a fraction of a second, and a small amount of secretion can turn litres of water into slime, enough to clog the gills of an attacking fish; underwater cameras have filmed sharks letting go and swimming off. Each thread is far thinner than a human hair yet strong and stretchy, so researchers study it as a model for new fibres. Afterwards the hagfish ties itself in a knot and slides the knot along its body to wipe the slime off.

HagfishRead card
WonderEvolution

Three-spined sticklebacks, small fish of northern seas, have moved into lakes and rivers again and again. Each time they tend to evolve lighter armour, often using a gene variant their sea-going ancestors already carried.

Sea-going sticklebacks carry 30 to 40 bony plates along each side, protection against predatory fish; most freshwater populations have between none and a dozen. A single gene called Eda (ectodysplasin) largely decides how many plates grow, and the low-armour version survives at low frequency in sea populations, ready whenever fish settle in fresh water. The change can be fast. In 1982, Loberg Lake in Alaska was poisoned to clear it for trout and salmon, and sea-going sticklebacks recolonised it. In the twelve years from 1990, the fully armoured form fell from the whole population to about one fish in ten, while a low-plate form rose to three in four. Because thousands of lakes were colonised separately after the last ice age, the same change has happened independently again and again.

Three-spined sticklebackRead card
Next card in the archiveDoggerland was a stretch of low-lying land, now under the North Sea, that joined Britain to continental Europe after the last ice age, until rising seas slowly drowned it.Read next →