(a) Monozygotic (MZ) twins result from the fertilization of a single egg by a single sperm. After on

(a) Monozygotic (MZ) twins result from the fertilization of a single egg by a single sperm. After one or more mitotic divisions, the embryo splits in two and forms two genetically identical individuals. (b) Dizygotic (DZ) twins result from the independent fertilization of two eggs by two sperm during the same ovulatory cycle. Although these two embryos simultaneously occupy the same uterine environment, they share only about half of their genes.


Monozygotic (MZ) twins
Single fertilization
event
* Mitosis
[CD
0 o
(a)
Two genetically
identical embryos
l
CD
(b)
Mitosis
Dizygotic (DZ) twins
l
(D
Two independent
fertilization
events
Two embryos sharing
about half their genes
© Cengage Leammg