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#cloning

28 public questions tagged with this topic.

Developmental biology Basics

The first cloned mammalian species confirmed after Dolly included:

Following Dolly in 1996, successful mammalian cloning rapidly expanded demonstrating technique not sheep-specific. In 1997-98, laboratories reported cloning in other species. Wakayama produced cloned mice via cumulus cell nuclear transfer, establishing repetitive cloning possibility. Polly transgenic sheep followed. Notably, researchers at Texas A&M and other groups confirmed cloning of rabbits and guinea pigs, small mammals with short gestation, using somatic cell nuclear transfer protocols adapted from Wilmut method. Frogs and chickens were not cloned by same mammalian SCNT approach; birds remain difficult due to meroblastic eggs. Humans and monkeys faced ethical restrictions and technical barriers until 2018 macaque cloning.

Ref: Wilmut et al., 1997; Wakayama et al., 1998; Gilbert, 12th ed., Chapter 3: Mammal cloning.

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Developmental biology Basics

Dolly the sheep later reproduced by which mode?

Dolly, despite originating via somatic cell nuclear transfer, possessed fully functional reproductive system with normal ovaries and estrous cycles. She mated naturally with Welsh Mountain ram named David and produced six lambs: Bonnie in 1998, followed by twins Sally and Rosie, and triplets Lucy, Darcy, and Cotton later. This demonstrated cloned animals could reproduce via conventional sexual reproduction, producing gametes through meiosis, fertilization, and embryonic development. Natural breeding success dispelled concerns cloning caused absolute sterility, though Dolly later developed premature arthritis and shortened telomeres raising questions about cloning associated epigenetic aging.

Ref: Wilmut & Campbell, Nature 1997; Gilbert, 12th ed., Chapter 3: Dolly reproduction.

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Developmental biology Basics

The concept that differentiated cells retain all genes needed for the entire organism is evidenced by:

If differentiation caused permanent gene deletion, differentiated cells could not generate entire organism. Cloning experiments overturn this idea by demonstrating nucleus from specialized cell retains complete genome. Transfer of intestinal cell nucleus in frogs by Gurdon and mammary cell nucleus in sheep by Wilmut yielded fertile adults, proving genetic totipotency persists despite cellular specialization. Morphogenesis, organogenesis, and fertilization do not directly test genome retention; they illustrate patterning processes. Cloning thus provides functional proof that phenotype differences arise from gene regulation, not gene loss, supporting equivalence principle central to epigenetics.

Ref: Gurdon & Wilmut, Development; Gilbert, 12th ed., Chapter 3: Cloning proves equivalence.

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Developmental biology Basics

Which cell type was used by Gurdon to clone frogs?

John Gurdon extended Briggs and King's earlier work by using fully differentiated somatic nuclei. Working with Xenopus laevis, he transplanted nuclei from tadpole intestinal epithelial cells into enucleated eggs and obtained normal tadpoles and adult frogs. Intestinal cells were definitive differentiated lineage possessing brush border enzymes, yet nucleus remained totipotent when placed in egg cytoplasm rich in reprogramming factors like histone chaperones and nuclear envelope disassembly machinery. Experiment proved terminal differentiation does not involve irreversible gene loss, providing key evidence for genomic equivalence and enabling later mammalian cloning strategies using adult somatic cells.

Ref: Gurdon, J Embryol 1962; Gilbert, 12th ed., Chapter 3: Tadpole intestine nuclei.

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Developmental biology Basics

Which scientist cloned Dolly the sheep?

Dolly cloning breakthrough credited to Ian Wilmut and Keith Campbell at Roslin Institute, Edinburgh, working with embryologist Bill Ritchie. Wilmut led somatic cell nuclear transfer project aiming to produce transgenic sheep for pharmaceutical protein production in milk. Using cell cycle synchronization inducing quiescence in donor mammary cells and electrical fusion with enucleated oocytes, team generated viable lamb. Published in Nature 1997, work demonstrated differentiated mammalian nucleus could be reprogrammed completely. Gurdon, Briggs, King pioneered amphibian cloning earlier; Aristotle founded ancient embryology but not associated with modern cloning methodologies.

Ref: Campbell et al., Nature 1996; Gilbert, 12th ed., Chapter 3: Wilmut and Dolly cloning.

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Developmental biology Basics

Which animal was the first sterile species successfully cloned?

Mules are sterile interspecific hybrids from horse and donkey parents with 63 chromosomes preventing normal meiotic pairing, exemplifying hybrid sterility. Cloning a mule addressed whether sterile hybrids retain complete diploid genome capable of somatic nuclear reprogramming. In 2003, Idaho Gem, a mule foal, was produced by somatic cell nuclear transfer from fetal fibroblasts at University of Idaho, becoming first cloned equid and first cloned sterile animal. Success proved sterility due to germ cell meiosis failure not lack of genomic competence, opening conservation of endangered or sterile hybrids. Sheep Dolly illustrated fertile mammal cloning earlier.

Ref: Woods et al., Science 2003; Gilbert, 12th ed., Chapter 3: Cloning of mule Idaho Gem.

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Developmental biology Basics

Dolly, the cloned sheep, was developed using a nucleus from which type of cell?

Dolly the sheep, born in 1996 at Roslin Institute, demonstrated mammalian somatic cell nuclear transfer could reverse differentiation. Nucleus from quiescent mammary epithelial cell of adult Finn Dorset ewe was fused to enucleated egg from Scottish Blackface ewe. After in vitro activation and implantation into surrogate, Dolly developed as genetic clone of donor. Choice of mammary gland illustrated differentiated adult cell retained full genetic information. Liver, sperm, and egg cells were not used as nuclear donors. Success proved genomic equivalence in mammals and opened regenerative biology and cloning research.

Ref: Wilmut et al., Nature 1997; Gilbert, 12th ed., Chapter 3: Dolly mammary nucleus.

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