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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Nuclear Transfer Techniques
Nuclear transfer is a technique used to create an identical genetic copy (a clone) of an organism. Unlike reproductive methods that combine genetic material from two parents, cloning produces offspring that are genetically identical to a single parent organism.
Key Definitions:
Scientists clone organisms for various reasons, including:
There are three main types of cloning:
Nuclear transfer techniques are primarily used in reproductive and therapeutic cloning.
Somatic Cell Nuclear Transfer (SCNT) is the most common nuclear transfer technique used in cloning. It involves replacing the nucleus of an unfertilised egg cell with the nucleus from a somatic cell of the organism to be cloned.
The process of SCNT involves several carefully controlled steps:
Scientists collect an egg cell from a female donor and a somatic cell (like a skin cell) from the organism to be cloned.
The nucleus of the egg cell is removed, creating an enucleated egg. This removes the egg's genetic material.
The nucleus from the somatic cell is transferred into the enucleated egg, usually using a fine needle or electrical fusion.
The egg is stimulated with chemicals or an electrical pulse to begin dividing as if it had been fertilised.
The dividing cell develops into an early-stage embryo in a laboratory culture.
The embryo is implanted into a surrogate mother where it continues to develop.
In 1996, scientists at the Roslin Institute in Scotland created Dolly, the first mammal cloned from an adult somatic cell. They took a mammary gland cell from a 6-year-old Finn Dorset sheep and fused it with an enucleated egg from a Scottish Blackface sheep. The resulting embryo was implanted in another Scottish Blackface sheep that acted as a surrogate mother.
Dolly was born on July 5, 1996 and was genetically identical to the Finn Dorset sheep that donated the mammary cell. She lived for 6.5 years (about half the normal lifespan of her breed) and developed arthritis and lung disease at a relatively young age. Dolly's creation proved that specialised cells could be reprogrammed to create a whole new organism.
Despite its potential, nuclear transfer cloning faces several significant challenges:
Despite its challenges, nuclear transfer has several important applications:
Scientists are using cloning to help preserve endangered species. In 2020, researchers successfully cloned the endangered black-footed ferret from cells that had been frozen for 30 years.
Cloning allows farmers to reproduce animals with desirable traits, such as high milk production or disease resistance, without relying on selective breeding over many generations.
Therapeutic cloning can produce stem cells that match a patient's tissues, potentially allowing for personalised treatments without rejection risks.
CC (Copy Cat) - 2001: The first cloned pet, a cat named Carbon Copy (CC), demonstrated that companion animals could be cloned.
Prometea - 2003: The first cloned horse, which later gave birth to a naturally conceived foal, showing that clones can reproduce normally.
Snuppy - 2005: The first cloned dog, which was more difficult to achieve than other mammals due to dogs' unique reproductive biology.
Zhong Zhong and Hua Hua - 2018: The first cloned primates (monkeys), bringing the technology closer to humans and raising new ethical questions.
Nuclear transfer is just one of several cloning techniques. Understanding how it compares to other methods helps clarify its unique advantages and limitations:
This technique mimics the natural process that creates identical twins:
A newer technique that reprograms adult cells:
As technology improves, nuclear transfer techniques are likely to become more efficient and find new applications. Some potential future developments include:
While nuclear transfer techniques offer many potential benefits, they also raise important ethical questions. Consider:
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