Viw Magazine

Men's Weekly

.

  • Written by Alison McEwen, Head of Discipline of Genetic Counselling, Graduate School of Health, University of Technology Sydney
Identical twins look the same, are the same sex, share the same birthday and shares the same genes. www.shuttershock.com , CC BY

If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au.


Why are some twins identical and some not? - Chloe, age 12, Australia

We have spent many years explaining how genes work to people who would like to have children, so we’re happy to answer this excellent question.

There are two types of twins: fraternal and identical.

Fraternal twins may be born on the same day but are not genetically the same. They look different, have different genes and may be of the same sex or the opposite sex.

Identical twins, on the other hand, look the same, share the same birthday and share the same genes. They are the same sex, meaning they will both be girls or they will both be boys.

To understand why, we need to look at what happens at the time a pregnancy starts. We call the start of a pregnancy the time of conception.


Read more: Curious Kids: Why do people grow to certain sizes?


What happens when a woman becomes pregnant?

Most women produce one egg each month. Each time a man and woman have sex, the man produces thousands of sperm. If the man and woman have sex and do not use contraception (for example a condom, IUD or the Pill), there is a chance that a sperm will fertilise the egg and the woman will become pregnant.

Most of the time, a single egg is fertilised, and goes on to develop into a single baby. If the egg is not fertilised, the woman will soon have her period, which is the way a woman’s body prepares itself for a new egg to be fertilised the next month.

We call a fertilised egg a “zygote”. This is a good word to remember, as we use it to help us understand the different ways identical twins develop during pregnancy (and knowing a word like zygote might impress your science teacher one day).

Identical twins have come from a single egg and a single sperm, so they share the same genes as each other. Heather/flickr, CC BY-NC-ND

How do identical twins happen?

As you may know, genes are the instructions that tell our bodies how to develop and grow. They are like a recipe for creating each of us as unique individuals.

We have two copies of each of our genes: one from our biological mother and one from our biological father. That’s why we look like both our mother and our father.

Identical twins happen when a zygote splits into two in the first few days after conception. They have come from a single egg and a single sperm, so they share the same genes as each other. The reason the zygote splits is thought to be inherited, which may be why some families have a few sets of identical twins.

Because identical twins come from a single zygote that splits in two, they have exactly the same genes – exactly the same recipe. They will both have the same coloured eyes and hair, and will look the same. Identical twins are always the same sex too – they will both be girls or they will both be boys.

How do non-identical twins happen?

Identical twins are also called monozygous twins. This just means that they have come from the same, single zygote (mono means “one”). Non-identical twins are sometimes called dizygous twins (di means “two”, so dizygous means two zygotes).

Earlier on, we said that most women produce one egg each month. Occasionally, a women will produce more than one egg in a month. Non-identical twins happen when a woman produces two eggs (in the same month) and both eggs are fertilised by two different sperm.

Unlike identical twins, non-identical twins do not share the same genes as each other. They grow together and share the same birthday, but they are only as related as any other brothers and sisters. Non-identical twins could both be girls, or both be boys, or could be one girl and one boy twin.

Identical twins come from a single zygote that splits in two. Non-identical twins happen when a woman produces two eggs (in the same month) and both eggs are fertilised by two different sperm. Shutterstock

Interestingly, there are more non-identical twins in Australia now than there have been before. The number of twin pregnancies has grown over the past 30 years. This might be partly because women in countries like Australia are having children when they are older and the chance of a twin pregnancy increases as women get older (as they are more likely to produce more than one egg in the same month).

The chance of a twin pregnancy is also higher if a couple uses assisted reproductive technology to help them to become pregnant.


Read more: Curious Kids: how do babies learn to talk?


Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au

Alison McEwen is the vice president of the Human Genetics Society of Australasia.

Chris Jacobs does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Authors: Alison McEwen, Head of Discipline of Genetic Counselling, Graduate School of Health, University of Technology Sydney

Read more http://theconversation.com/curious-kids-why-are-some-twins-identical-and-some-not-121435

VR Training in Australia – Conflict Resolution Training For Employees

In today’s rapidly evolving workplaces, Australian organisations are turning to immersive learning tools like VR to handle specialised n...

Financial Planning For Couples

Why Every Couple Should Talk About Money And A Will (Before It’s Too Late) When you’re in a new, exciting relationship, it’s easy t...

Navigating Relationships While Living with Depression

Living with depression can feel like carrying an invisible weight—one that not only affects how you experience the world but also how yo...

Choosing the Right Vinyl Flooring Suppliers for Your Home or Business

When it comes to selecting flooring options that combine durability, style, and affordability, vinyl flooring stands out as a top choice. ...

Why Food Manufacturing Cleaning Services Are Essential for Safety and Quality

The complexity of food production environments demands specialised cleaning approaches that go beyond regular janitorial work. This is whe...

The Importance of Choosing the Right Industrial Electrician Melbourne for Your Business

When it comes to powering large-scale operations and complex machinery, commercial electrical services are not enough. Industrial environm...

What to Expect During a Property Settlement After Separation

Separation is a challenging and emotional time, and one of the most complex aspects can be the division of property. However, understandin...

Designing the Ideal Healthcare Environment with a Professional Medical Centre Fitout

When it comes to healthcare spaces, functionality, hygiene, and patient comfort take top priority. An intelligently designed medical centr...

Stay Comfortable Year-Round with Ducted Cooling Melbourne

When the temperature starts to rise, having a reliable and efficient cooling system becomes a priority. With unpredictable weather and sud...

Best Practices for Content Ownership and Tagging Across Departments

Image by kaboompics on Freepik The bigger and more complex content ecosystems grow, the more valuable ownership and tagging become. In ent...

Understanding Public Liability Insurance Australia: What You Need to Know

Image by rawpixel.com on Freepik The necessity of public liability insurance in Australia is that it acts as a financial safeguard for busi...

How HID Proximity Cards Improve Workplace Security Without Slowing Down Access

In today’s workplaces, security is non-negotiable, but so is speed. Companies are under pressure to protect their people, property, and ...

Unlock Business Insights Faster with Power BI Tools

In this digital age where data drives the consumer landscape, businesses are shipping huge amounts of data every day. To remain competit...

Why Split System Installation Is a Smart Choice for Home Climate Control

Temperature control is essential for comfort, and when it comes to efficient, versatile cooling and heating, a split system is one of the ...

The Ultimate Guide to Door Replacement: Everything You Need to Know

Image by freepik Sure, swapping out a door is a fairly easy task, but it requires careful consideration of options for materials, designs...

Common Web Development Issues Perth Businesses Face (and How Agencies Fix Them)

Image by freepik Let's be honest, in the bustling heart of Perth's business scene, a website that's not up to scratch is like trying to he...

Life With Clear Aligners: 10 Small Changes That Make a Big Difference

Image by tonodiaz on Freepik Clear aligners have transformed orthodontics, offering a nearly invisible way to straighten teeth without the...

Choosing the Right Hair Loss Treatment for Your Needs

Millions of people experience hair loss globally, and it can be a major cause of emotional discomfort and self-consciousness. Hair loss ca...

Cardboard Display Boxes: An Effective Solution for Retail Presentation

In the competitive world of retail, how products are presented can be just as important as the products themselves. Cardboard display boxe...

Why Hiring a Skilled Shopify Web Developer Can Transform Your Online Store

Shopify has become one of the most popular e-commerce platforms due to its ease of use, powerful features, and scalability. However, creat...