Twins

Monozygotic (Identical Twins)

• Happens when one sperm fertilized a mature egg and then later the fertilized egg divided into 2,3,4… which results to the formation of two identical individuals.

Note: for the previous slide you can see the details on our pdf page 330-331

Dizygotic (FraternalTwins)

• When a woman releases two eggs at the same time, and was fertilized by two different sperm, then it would result to the formation of two non-identical individual..

Conjoined (“Siamese”) Twins

• 1/200000 • 40 – 60 % stillborn • 35% survive in just a day• The overall rate of survival rate of a conjoined twins is somewhere between 5 – 25%• http://umm.edu/programs/conjoined-twins/facts-about-the-twins• 70% of conjoined twins and the reason for which is unknown • . http://phreeque.tripod.com/conjoined_twins.html?

How?

1.Fission theory:• widely accepted• Conjoined twins occur when a

fertilized ovum splits into two and begins to form into an identical twins, but is somehow interrupted during the process and develops into two partially developed individual who are stuck together.

2. Fusion theory• According to this theory, twins

conjoined together after a fertilized egg initially splits into identical twins while lying side-by-side in the uterine wall the two embryos become fused together.

A BABY WAS FORMED IN 2005WITH A CONJOINED HEAD THAT HAD NO BODY. THE HEAD COULD BLINK AND SMILE.

Types of Conjoined Twins

ThoracopagusJoined at the upper chest, from the clavicle to the sternum, each with their own separate heads, arms and legs.

Thoracopagus twins are the most common type, accounting for around 35% of all cases.

Omphalopagus

Joined at the abdomen, from the sternum to the groin and often sharing a liver and portions of the digestive system.

About 30% of cases.

Ischiopagus

Joined at the ischium (front pelvis) and lower spine (sacrum), with spines at 180-degree angles to one another.

These twins can have three legs (tripus) or four legs (tetrapus).

About 70% of ischiopagus twins have four complete legs

Dicephalus

Twins share a body from the neck or upper chest downward, having only two legs and one set of reproductive organs.

Craniopagus

Joined by a portion of the skull, with distinctly separate necks and bodies.

Cephalothoracopagus

Twins with conjoined heads, necks and chests, with separate arms and legs.

These usually share a heart as well as a brain and are also non-viable.

Parasitic Twins

• Occurs when one of the embryo ceased to exist and later attached itself to the other embryo

• Autositic: parasite twins

EVERY 30 SECONDS,

A BABY IS BORN

WITH BIRTH DEFECTS

IN CHINA.

Twins can have

different biological fathers

In rare cases, twins can be different races.

If a pair of identical male twins marry a pair of identical female twins, their children will legally be cousins but genetically be full siblings.

Tall women are more

likely to have twins

Women

who eat a

lot of dairy

are also

more likely

to have

twins

Cheng and Eng Bunker

Donnie and Ronnie Galyon

Eliza and Mary Chalkhurst

Giacomo and Giovanni Battista

Abby and Brittany Hensel