Introducing Genetics E-Book

Steve Jones

• Herausgeber: Icon Books
• Kategorie: Wissenschaft und neue Technologien
• Serie: Graphic Guides
• Sprache: Englisch

Seitenzahl: 80

Veröffentlichungsjahr: 2014

Beschreibung

Genetics is the newest of all sciences - nothing useful was known about inheritance until just over a century ago. Now genetics is exploding, and before long we will have the complete code, written in three thousand million letters of DNA, of what makes a human being.  Introducing Genetics takes us from the early work of Mendel to the discovery of DNA, the human gene map and the treatment of inborn disease. No one can afford to be ignorant of genetics. This book is the perfect introduction.

Leseprobe

Published by Icon Books Ltd, Omnibus Business Centre, 39-41 North Road, London N7 9DP email: [email protected]

ISBN: 978-18483-1781-9

Text copyright © 1993 Steve Jones Illustrations copyright © 1993 Borin Van Loon

The author and artist have asserted their moral rights.

Originating editor: Richard Appignanesi

No part of this book may be reproduced in any form, or by any means, without prior permission in writing from the publisher.

Contents

Cover

Title Page

Copyright

Genetics is About Differences…

Cells, Genes and Jargon – A Summary

Heredity

People mentioned in the text

Footnote

Further Reading

About the Author

About the Illustrator

Index

…between people, or any other creature, large or small.

Genes are the record of biological history. Maps of how they are arranged say a lot about how humans evolved, how we are related to other creatures and even how life began.

Much of genetics is geography, on one scale or another.

But genetics began long after the world was explored, …

… and later than any other biological science — because, unfortunately, the obvious has usually turned out to be wrong.

You’re so obvious that you must be wrong, dahling!

For a thousand years people believed that relatives look alike because they shared the same environment and that experience changes the way you look.

It’s perfectly plain! Yes, children, his mother was jostled by a circus elephant when she was expecting.

Laban says I can keep all the spotted ones!

This is the twentieth generation, and – damn it – still they’ve all got tails! But jews have been doing the same thing for years!

Well, if that doesn’t work, perhaps children are the average of what went before. Darwin liked the idea that children were formed by mixing the blood of their parents. After all, his own family was pretty blue-blooded.

Well, I liked it at first.

Soon he read a nasty little article by Fleeming Jenkin, a Scots engineer. It pointed out a fatal flaw: if inheritance works like this, then any favourable character will be diluted out each generation until it disappears. The theory of evolution would not work! Jenkin had typically racist views…

o.k. You chaps, let me have the pick of your wives!! I am british, after all… Now, I Want Volunteers to fetch my baggage the voice of fleeming jenkin crazy white boy

Ho, My dearest… to my hut tonight! if you insist, you peculiar little man

Soon, Darwin’s cousin, Francis Galton, got interested. Galton was a strange, unlikeable man.

My cousin’s a genius, and so am i!

Like most Victorian scientists, he was rich. Unlike his cousin he completed his medical course (although he never practised). During it, he tried every drug in the book in alphabetical order, giving up at the purgative Croton Oil.

Galton travelled in Africa, riding on a bull into a chief’s house to frighten him into submission and measuring his wives’ buttocks with his naval sextant. He was interested in the inheritance of “genius” (judges were one example).

They seemed to turn up again and again in the same family. Perhaps genius was passed through the generations. But how? Could it really be mixing of bloods? He tried transfusing blood from a black rabbit into a white one.

But the offspring are white. Blackness is not in the blood!

Galton died, childless, in 1911. He left a fortune to found the Laboratory for National Eugenics at University College London.

The plan was to improve the human race!

This would be difficult until the mechanism of inheritance was worked out. In 1900, genetics seemed to be getting nowhere. At the time, five hundred miles was a long way, at least if it was outside the Empire.

In Brünn, now in the Czech Republic, another failed student — Gregor Mendel, who had studied science at university but gave up — had become interested in inheritance at about the same time as Galton.

He had more sense than Galton; he studied not humans but peas. They had all kinds of advantages — clean, easy to keep, and the divorce rate was low. What’s more, each plant was both male and female, and could fertilize itself.

Well, if I can’t have sex, at least the peas can. So THIS is what they mean by sex with someone you really love.

Farmers had bred many different pure lines of peas: within a line every plant was the same; between lines they were different.

Mendel realized that this is just what was needed to study how inheritance works. He fertilized seeds from a line with round peas with pollen from another line with wrinkled seeds.

All the offspring of this cross were round — not the average of their parents at all, but like only one of them.

But I preferred the wrinkled ones!

Then, Mendel grew up these round peas, and self-fertilized them; he put pollen onto the eggs of the same plant. When he grew these up — a big surprise: both types, round and wrinkled, came back again!

Well at least there’s some of the ones I like!

Perhaps there’s more to peas than the way they look! They might carry some concealed instructions which do not always reveal what they say; a round pea could contain hidden within itself the instruction for wrinkles.

Mendel suggested that pollen and egg each carried a particle (called a gene nowadays) containing the code for the shape of the pea in their offspring.

Hello, I’m just feeling round!

Today we know that the same rules apply for sperm and egg in animals.

When pollen met egg, the offspring had two particles or genes. Sometimes, one particle hid the effects of the other.

In the pure lines, round or wrinkled, every plant had two round or two wrinkled genes. When round from one pure line was crossed with wrinkled from another, all their offspring had one “round” and one “wrinkled” gene.

The effects of the round gene hid those of the wrinkled, and they all looked round.

This must explain my ratios! Well they still taste a bit wrinkled to me!

Round was dominant to wrinkled, which was recessive.

In the next generation all these round peas had two different genes. They therefore made two kinds of pollen or eggs; half with round and half with wrinkled particles or genes.

When they were self-fertilized, one time in four, “round” pollen met “round” egg; another time in four “wrinkled” met “wrinkled”; and twice in every four, “round” and “wrinkled” got together to give a round pea. Add them together, and Mendel’s magic three to one ratio of round to wrinkled peas in the next generation was explained!

Mendel did it again with yellow and green peas, or with tall and short. He got the same result each time; and it worked for every character he chose. What’s more, the shape of the pea made no difference to how colour was inherited. The genes were independent.

Genetics was, it seemed, based on particles passed from parents to offspring. It all seemed so simple.

Alas, it wasn’t. He moved on to study other plants which have complicated patterns of inheritance; and his laws seemed to fall to pieces. Like Galton and Darwin, he suffered from attacks of depression, and withdrew into administration.

Woe is me.

Mendel’s paper Versuche über Pflanzenhybriden (Experiments on Plant Hybridization) was published in 1866 in a little-known journal, the Transactions of the Brünn Natural History Society. He sent it to the most eminent biologists of his day, but it was ignored.

This Mandelism is a damp squib!

They were interested in a much bigger question. Now we know that they were asking the right question at the wrong time. They had no chance of answering it — and it remains unsolved. How does a fertilized egg with no structure of its own develop into the incredible complexity of a human being — or a pea?

Unin teresting tosh! Soon everyone was doing it. Humans came next.

Obviously, humans cannot be crossed together like peas. Or can they? Frederick the Great of Prussia had been quite successful in mating tall men with tall women to get some impressive guards for his palace.

Most of the time, human genetics has to wait for nature’s experiments. People choose their own mates.

I’ve always fancied big women.

Often, family history is recorded in a pedigree — from the French pied de grue, crane’s foot, after the way the lines splayed out from the centre in some ancient family trees.

It doesn’t look much like a foot to me!

The first genetical pedigree was simple: Short clubbed fingers in a Norwegian family was controlled by a dominant gene. Anyone who received a single copy of the gene had short fingers. Once it was lost from a family line, short fingers never came back.

The generations — parents, children and grandchildren — are shown on succeeding lines. Women are marked as circles, men as squares (seems very unfair!). People with short fingers have the symbols blacked in. Husbands and wives are not marked: they all had normal fingers. Everyone with short fingers has a short-fingered parent; and, on the average, half the children of such parents have short fingers.

Dominant characters seemed simple enough. Soon, characters controlled by recessive genes began to turn up. Only those inheriting two copies of the gene, one from each parent, showed its effects.

Gad, sir, just like his Great Uncle Albert.

Such traits cropped up in families, often skipping generations. This explained an old problem — atavism; the tendency of a child to resemble a remote relative or distant ancestor.

The first case of recessive inheritance was albinism: Most parents of an albino child were normal and if an albino married a normal person, their children usually had normal skins. The earliest known albino was Noah. As the Book of Enoch says, “his hair was white and fine as snow”.