What is a Chromosome?

Created by

Sarah Washbrook for Foundation for Angelman Syndrome Therapeutics UK

10 April 2025

• Understand what makes you YOU!

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• A basic understanding of cells, chromosomes, DNA and genes

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• Apply this to the real world

Learning Objectives

What Are Our Bodies Made Of?

• Cells
• Chromosomes
• DNA
• Genes

Let’s explore each in more detail!

Image from BBC Bitesize

Cells

• All life on Earth is made from cells
• Cells are the basic building blocks of all animals and plants
• Almost all cells are so small that you need a microscope to see them

There are more cells in the human body than the number of seconds in one million years.

You can fit 15,000 human cells into a single grain of sand.

Chromosomes

• A chromosome is inside the nucleus (or middle) of a cell
• It’s a threadlike packaging for our DNA and genes. (We’ll find out what these are in a moment..)
• Each human body cell contains 23 pairs of chromosomes (46 in total)
• Half of our chromosomes come from our mother, and half from our father - this is why we resemble both of our parents!

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Each species of plants and animals has a set number of chromosomes

Chromosomes

Guess how many pairs of chromosomes each of the following species have...

Chromosomes

ANSWERS - Was it what you expected?

23

39

4

48

DNA

• Each of our chromosomes contains DNA (DeoxyriboNucleic Acid)

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• DNA has all the information that a living thing needs to grow, reproduce and function

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• It is our own personal INSTRUCTION BOOK!

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• The DNA in most of our cells is very thin and about two metres long

DNA

Try to fit this 2 metre piece of string in your hand

If all the DNA in your body was stretched out end-to-end, it would reach from the Earth to the Sun and back over 600 times!

ACTIVITY

Genes

• A gene is a section of our DNA that is responsible for a particular characteristic or trait (like eye colour) or function (like being being able to roll your tongue, or good reflexes)

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• Humans have around 20,000 - 25,000 genes in every single cell (and we have trillions of cells in our body!).

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Genes

What percent of our genes do you think we share with each of the following?

Genes

ANSWERS! Was it what you expected?

98%

90%

20%

50%

Recap!

• The cell is the book

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• The chromosomes are the chapters

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• The DNA is the paragraphs

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• The genes are the words

Genetic Disorders

• Ivor, aged 5, has Angelman syndrome
• People living with Angelman syndrome have a genetic difference on chromosome number 15
• Ivor has two dad copies of chromosome 15 - meaning that there is one important gene (called UBE3A) that is turned off and not functioning as it should
• This gene controls a protein involved in brain functioning that helps us walk, talk and perform many other everyday tasks
• Apart from this one gene he is the same as you

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Genetic Profiling

• Every human has unique DNA

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• This is like a fingerprint

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• Identifying a person’s unique DNA is called Genetic Profiling

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• It has many amazing uses

Identical twins share the same DNA as they both came from the same original cell

Genetic Profiling Examples

It helps us catch criminals

• Forensic scientists can use DNA to help catch criminals by proving that they were at a crime scene
• They collect human cells left at a crime scene (from blood, saliva or hair)
• They then extract DNA from the cells, analyse it and make a DNA profile
• The DNA profile is then checked against a database of other profiles. If there is a match, it could be used as evidence

Forensic scientists have used this technique to solve crimes that happened 40 years ago!

Image from genome.gov

Genetic Profiling Examples

We can find out our ancestry

• Scientists can look for small variations in DNA that are inherited and compared against databases of DNA from people around the world
• Your ancestry results could reveal you are 25% Scandinavian and 25% Southern European!
• Some tests can trace your ancestry back thousands of years

A soldier who died in a battle in World War I in 1915 was identified using genetic profiling as Private Harry Wilkinson 86 years later!

Genetic Profiling Examples

We can create personalised medicines

• Everyone’s body is a bit different, personalised medicine uses your DNA to find the best treatment for you
• Doctors can check your DNA to see which medicines work best, or which ones might give you side effects
• Doctors use science to pick the medicine that fits your body, like a key fits a lock
• Your DNA can tell you if you’re more likely to get certain illnesses, so you can take action early

Genetic Profiling Examples

We can diagnose, treat and find cures for genetic conditions

• Doctors can look at your DNA to find out if you were born with a gene that causes illness or impairment
• New science lets doctors change or replace faulty genes — it’s like giving your body the right instructions!
• Science is moving fast — some conditions that used to be deadly can now be treated or even cured
• For example, clinical trials are looking to treat Angelman syndrome by “turning on” the dad’s switched off housekeeping gene

Genetic Profiling

Genetic profiling can be controversial though

• Storage of DNA profiles can be seen as an invasion of privacy, it could be stolen and it could be “used against us”
• If an insurance company or your future employer saw your genetic profile would that be fair?
• Ethical considerations - should we dabble with the way humans are made?

Is genetic profiling good or bad?

What is your opinion?

discussion

Summary

• You should now have a better understanding of what makes you YOU…
• …in terms of of cells, chromosomes, DNA and genes.
• You should be able understand how we can apply this to the real world.

Let's look back at our learning objectives

Our bodies are amazing!

Genetic scientists are amazing!

What we can do with this knowledge is amazing!

Make Your Own Chromosome

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• We’re going to make a simplified model of a pair of chromosomes that represents your own physical characteristics

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• We will then compare your models

ACTIVITY

Make Your Own Chromosome

• What is a trait/characteristic?
• Can you name any traits that your friends have?

Our individual physical traits (e.g. eye and hair colour) are determined by our genes, which are grouped together on DNA and packaged into chromosomes.

discussion

recap

Make Your Own Chromosome

• Get two pipe cleaners each.
• Make an “X” and twist together in the centre. This represents a pair of chromosomes - the structure that holds genes
• Look at your Handout and circle the traits that you have and the corresponding bead colour that represents that trait. Each bead colour represents the set of genes for that trait. Partner up if you want!
• Collect the colour beads that represent your genes
• Lace them on to any of the four sections of your pipe cleaners
• Bend the four corners so the beads don’t fall off

Make Your Own Chromosome

Result!

• You have created a simple model of a pair of chromosomes that represents YOU!

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• Compare and contrast your own chromosome model with others in the class

Follow-up Learning

• Create a chart on the board that tallies the number of students that have each trait
• Why are some traits collectively found in everyone?
• Why are some traits not found in everyone?
• Which are some of the traits that occur the most often (high frequency) and the least often (low frequency)?
• High frequency traits can vary, depending on the population. For example, the high frequency traits for a small, secluded population living on an island may be very different from those living in a densely populated city
• Why would a scientist study high frequency traits in the human population?
• What are examples of non-observable human traits?
• Extend the activity by having students perform the same experiment with another class or group of students, or “population.” Compare and contrast the results. Are they surprised by the results? What are possible reasons for similar or different results?

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