Natural Cloning

Define natural cloning in an animal context.

• The production of offspring that are genetically identical to the parent or to a sibling, occurring naturally without human laboratory intervention.

State two examples of natural cloning in invertebrate animals.

• Starfish: Can regenerate a completely new, cloned organism from a fragmented/severed limb.

• Aphids (Greenfly): Females can naturally produce genetically identical diploid eggs that develop into live cloned young without fertilization (a process called parthenogenesis).

Describe the step-by-step process of how monozygotic twins form (embryo splitting).

• A single ovum (egg) is fertilized by a single sperm to form a single diploid zygote.

• The zygote undergoes mitosis to form a small ball of cells (an early embryo).

• For unknown reasons, this early embryo completely splits into two separate masses of cells.

• Because the cells are still totipotent (able to develop into any cell type), each separate mass develops into a complete, full-term fetus.

Why are dizygotic (fraternal) twins NOT considered clones?

• Dizygotic twins form when two different eggs are fertilized by two different sperm at the same time.

• They only share about 50% of their DNA, making them no more genetically similar than standard siblings born years apart.

Are monozygotic twins perfectly identical phenotypes at birth?

No. Even though their genetic code (genotype) is 100% identical, environmental factors in the uterus (like slight differences in blood supply or positioning) will cause slight physical differences, such as unique fingerprints.