Turn on more accessible mode Turn off more accessible mode Skip Ribbon Commands Skip to main content Turn off Animations Turn on Animations Our Sponsors Log in | Register Menu Log in | Register Home Our Sponsors
AbdominalADHDAllergies ＆ AsthmaAutismChest ＆ LungsChronic ConditionsCleft ＆ CraniofacialCOVID-19Developmental DisabilitiesEar, Nose ＆ ThroatEyesFeverFluFrom Insects or AnimalsGenitals and Urinary TractGlands ＆ Growth DisordersHead, Neck ＆ Nervous SystemHeartInfectionsLearning DisabilitiesObesitySeizuresSexually Transmitted InfectionsSkin ConditionsSurgical ConditionsTreatments
Injuries ＆ Emergencies
Sports Injuries
Vaccine Preventable Diseases
NewsNews
Tips & ToolsTips & Tools
Tips and Tools
Ask The Pediatrician
Asthma Action Tracker
AAP Family Media Plan
Find a Pediatrician
Healthy Children Magazine
Healthy Children Podcast
Healthy Children Texting Program
Motor Delay Tool
Newsletters
Physical Activity Checker
Symptom Checker
Webinars
Our MissionOur Mission
Our Mission
AAP in Action
Medical Editor & Contributors
Sponsors
Sponsorship Opportunities
Spread the Word
Shop AAP
Find a Pediatrician
Family Life
Family Dynamics
Adoption & Foster Care
Communication & Discipline
Types of Families
Getting Involved in Your Community
Media
Medical Home
Power of Play
Work & Child Care
In This Section Healthy Children > Family Life > Family Dynamics > The Difference Between Identical and Fraternal Twins Family Life The Difference Between Identical and Fraternal Twins
(Hidden) Content Editor
Page Content Article Body
Because fraternal, or dizygotic, twins are 2 separate fertilized eggs, they usually develop 2 separate amniotic sacs, placentas, and supporting structures. Identical, or monozygotic, twins may or may not share the same amniotic sac, depending on how early the single fertilized egg divides into 2.
If twins are a boy and a girl, clearly they are fraternal twins, as they do not have the same DNA. A boy has XY chromosomes and a girl has XX chromosomes. Girl-boy twins occur when one X egg is fertilized with an X sperm, and a Y sperm fertilizes the other X egg.
Sometimes health care professionals identify same-sex twins as fraternal or identical based on ultrasound findings or by examining the membranes at the time of delivery. The best way to determine if twins are identical or fraternal is by examining each child’s DNA. Occasionally a family is told that their twins are fraternal based on placenta findings, when they are in fact identical. Other times, a family may see the minor differences in identical twins and declare the twins fraternal based on these differences in appearance. There are a few commercial laboratories that, for a fee, will send families DNA collection kits to determine if the twins are identical or fraternal. The families swab the insides of each child’s cheek for a DNA sample and send the kit back to the laboratory to await results.
Identical twins have the same DNA; however, they may not look exactly identical to one another because of environmental factors such as womb position and life experiences after being born. Our family joke about one of our twin’s stitches for a lacerated upper lip was that he wanted to distinguish himself from his identical twin brother! In addition to life’s bumps, bruises, and differing hairstyles, a child’s DNA is constantly adapting to that child’s experiences. Different stretches of one’s DNA can turn on or off in response to environmental surroundings—therefore, over time, a pair of identical twins’ DNA becomes more and more distinctive. All twins, whether fraternal or identical, are truly 2 separate, unique individuals.
Turn on more accessible mode Turn off more accessible mode Skip Ribbon Commands Skip to main content Turn off Animations Turn on Animations 
Our Sponsors Log in | Register Menu Log in | Register Home Our Sponsors Find a Pediatrician