As a student of biology when ever I come by artificial cloning, I always find examples of females being cloned - Dolly the sheep, CopyCat, Daisy, etc. The only male I could see was Fibro mouse and a few more. What is the reason behind this? Is the male genome more difficult to be cloned? I am specifically looking for genetic reasons or other complications.

  • $\begingroup$ It might just be a case of they take the sample from the same animal they are using the eggs from for ease of access. $\endgroup$
    – SolarLunix
    Aug 5, 2015 at 15:58
  • $\begingroup$ @SolarLunix I dont think this can be the reason. By the way, thank you. $\endgroup$ Aug 5, 2015 at 16:02
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    $\begingroup$ What exactly do you mean by "cloning"? Somatic cell nuclear transfer? Making transgenics/knockouts/other genetically-modified organisms? Please edit your question to add additional information, as well as some literature citations supporting your observations, as currently this just appears to be anecdotal evidence. There is no difference between the male and female genomes, obviously excepting the sex chromosomes. $\endgroup$
    – MattDMo
    Aug 5, 2015 at 16:12
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    $\begingroup$ No there is no problem as such. However, a female can produce her own clone but a male cannot. $\endgroup$
    Aug 5, 2015 at 17:07
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    $\begingroup$ You can maintain some of the genetic traits in progeny if you clone a female, since it, as a female, can give birth. A male would be a more difficult model to work with if you were studying genetics. If anything, because females have more genetic content (x is bigger than y), the success rate of the micro injections for females I would be willing to bet are a little less successful. But I'm just guessing here in all honesty about my last statement. @RehanUllah $\endgroup$
    – rhill45
    Aug 7, 2015 at 4:08

1 Answer 1


They aren't, anymore. It was a fair guess at the time, but first I think we should define what cloning in this context mean.

Our own tag says:

The process in nature or in the lab by which a new organism is created that is genetically identical to its predecessor.

For animals - I'm going to use Dolly as an example since you do as well - when we say "cloning" we usually mean somatic cell nuclear transfer. This image from Wikipedia sums up the process:

Somatic cell nuclear transport

Basically, you take the nucleus of your to-be-cloned animal and put it inside the egg cell from another animal. Dolly was not produced by one animal but by two - a donor and and a surrogate. She was made using mammary tissue (another good image here) from the donor, which is important to note.

Dolly was the only one out of 277 egg cells that made it. This is a hard technique, and we still don't understand a lot of it. With even less information at the time, some prevailing ideas were:

  • Maybe there's something special about reproductive-based tissue
  • Maybe there's something special about female tissues

Even when using a different technique (e.g. Cumulina), early cloning attempts hedged their bets with those same tissues. That's why Fibro, the first male cloned (from tail), was a big deal - he showed that any tissue could be used, and that reproductive or female tissue wasn't inherently special. You still need an egg and a surrogate, but if you can get the nucleus right it's just as doable.

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    $\begingroup$ I'd also make the case that, where the XY sex system is in place, anything genetic with a Y chromosome is inherently less stable. But that's my opinion. $\endgroup$
    – Amory
    Aug 5, 2015 at 23:44
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    $\begingroup$ Nice explanation. Thank you for the valuable images. $\endgroup$ Aug 6, 2015 at 3:38
  • $\begingroup$ @Amory A nitpick - If I understand correctly, the image from Wikipedia is somewhat misleading, as the whole somatic cell is fused with the enucleated egg (i.e., we don't use solely the nucleus of the somatic cell). See another question. $\endgroup$ Aug 11, 2019 at 20:11

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