Natural Clones in Animals (OCR A Level Biology)

Revision Note

Test yourself
Phil

Author

Phil

Last updated

Natural Clones in Animals

Asexual reproduction in animals

  • Asexual reproduction is much less common in animals than in plants
  • Some small animals reproduce asexually by parthenogenesis eg. aphids
  • The other naturally occurring incidence of cloning in animals is identical twins

Identical twins

  • An egg is fertilised by a sperm as in a singleton birth
  • This forms a zygote
  • The single zygote undergoes a few cell cycles (mitotic divisions) to become an embryo
    • This is why identical twins are referred to as monozygotic

  • At the embryo stage, the embryo splits in two; the exact causes of this kind of split are not well understood
  • Two embryos that form are identical, with the same genotype and develop in utero together
  • The result is the birth of identical offspring, always of the same gender, with identical phenotype
  • Because non-identical twins are formed from separate eggs and sperm, they are not considered clones

 

Examiner Tip

Although identical (monozygotic) twins share the same genome at the moment when the embryo splits, identical twins are not clones in the true sense of the word. Because mutations occur with every cell cycle, Twin A will possess slightly different DNA base sequences to Twin B at the time of birth. The older the twins get, the more their genomes become dissimilar as mutations accumulate. They will still look very alike throughout their lives unless there are large differences in their environments as they grow up.

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Phil

Author: Phil

Expertise: Biology

Phil has a BSc in Biochemistry from the University of Birmingham, followed by an MBA from Manchester Business School. He has 15 years of teaching and tutoring experience, teaching Biology in schools before becoming director of a growing tuition agency. He has also examined Biology for one of the leading UK exam boards. Phil has a particular passion for empowering students to overcome their fear of numbers in a scientific context.