← Bungalow23Bungalow23 · body awareness

23 pairs: what your chromosomes actually are

The bungalow is named after them. Matron Iris and Gran Hazel finally sit down and count.

Bungalow23 takes its name from a number you carry in nearly every cell you own. Twenty-three. This week Gran Hazel asks the obvious question, and Matron Iris brings the textbook.

The lived body

Gran Hazel is a midwife's daughter. She grew up hearing families argue over a newborn's nose. Grandad's, surely. No, it's Aunty June's.

Gran Hazel: "Every family has that conversation over the cot. I always thought it was the nicest kind of argument. Everyone wanting a bit of themselves in the baby."

Her question is simple. What is actually being passed down, and where does it live?

The evidence

Matron Iris: "Start small. MedlinePlus Genetics, which is run by the US National Library of Medicine, says that in the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes."

Each chromosome is DNA coiled tightly, many times, around proteins called histones that support its structure. Each one has a pinched point called the centromere, which divides it into two sections. The short arm is called the p arm, and the long arm is the q arm.

And the count? MedlinePlus says each human cell normally contains 23 pairs of chromosomes, 46 in total. Twenty-two of those pairs are called autosomes, and they look the same in males and females. The 23rd pair are the sex chromosomes. Females typically have two X chromosomes, and males typically have one X and one Y.

Gran Hazel: "So that's the bungalow. Twenty-three rooms, two of everything."

Matron Iris: "Near enough. I'll allow it."

Down to the genes

Inside the chromosomes is DNA itself. MedlinePlus describes it as the hereditary material in humans and almost all other organisms. Its code is written in four chemical bases: adenine, guanine, cytosine and thymine, usually shortened to A, G, C and T. Human DNA has about 3 billion of those bases, and more than 99 per cent of them are the same in all people.

A gene is a stretch of that DNA, the basic unit of heredity. MedlinePlus notes that recent research puts the number of protein-making genes in the human genome at about 19,900. Typically, people have two copies of each gene, one inherited from each parent. Small differences between versions of the same gene are called alleles, and they contribute to each person's unique physical features.

Most of your DNA sits in the nucleus. A small amount lives elsewhere, in the mitochondria, the parts of the cell that convert energy.

The friendly argument

Gran Hazel: "So the nose argument is about alleles."

Matron Iris: "Partly. But genes aren't the whole story of a person, and I'd be careful with anyone who tells you they are."

Hazel agrees, and adds her own line. The family argument over the cot was never really about the nose. It was about belonging.

Where they land

Twenty-three pairs, about 3 billion bases, two copies of most genes, and more than 99 per cent shared with every other person on the planet. Iris finds that last number tidy. Hazel finds it moving. Both of them think it would make a decent motto for a newsroom.

If you have questions about genetics and your own health or family, that is a conversation for a professional who knows your history.

Sources

Please note

Talk to your GP or health professional about your own body.

Bungalow23 is body awareness, not medical advice. N.A.N.A. presenters are AI characters.