Childrens Illustrated Encyclopedia

Cloning dolly

Clones are one or more identical

organisms that share identical genes but,

unlike twins, are not produced by natural

reproduction. For many years, scientists have

been interested in cloning identical copies of

animals and plants. in 1997, scientists successfully

cloned a sheep, known as dolly. The experiment led to

a worldwide debate about the ethics of cloning.

The world’s media took a

great interest in Dolly, the

first large mammal

to be cloned.

Twins

if a fertilized human embryo splits in

two it will develop into identical twins.

Each twin shares the same genetic

information. in fact, they are not

entirely identical, because each fetus

develops in a slightly different way after the

original split. Therefore, identical twins can

appear to be remarkably similar yet have quite

different personalities. non-identical twins

develop from two separate embryos.

The cats produce

male and female

kittens. Only females

can be tortoiseshell.

Gregor

Mendel was

an ordained

priest and

combined

religion with

his work as

a scientist.

MEndEl

gregor Mendel (1822-84), an Austrian

scientist, discovered the laws of heredity

through experiments with pea plants.

in 1866, he showed that features

in a plant, such as the production

of a smooth or a wrinkled pea, are

determined by the genetic information

given to the plant by its parents. He

called this information “particles,” some

43 years before the word “gene” was

invented by the danish scientist

wilhelm Johannsen (1857-1927).

genetics

230

PATTErns oF inHEriTAnCE

different forms of the same gene are called alleles, and they

can be dominant or recessive. dominant alleles always show

up, even if the information they carry comes from only one

parent. recessive means that a certain feature might not be

seen in a plant or animal even though it is carrying the right

alleles. recessiveness is sometimes linked to gender.

gM Foods

The plants and animals that

produce gM (genetically modified)

foods have had their genes

changed by scientists. in theory,

genetic modification is just a

way of speeding up the process

of selection by breeding, which

is already done in the natural

way. There is much to be learned

before we can be sure that genetic

modification is a safe thing to do.

Atoms and molecules

radioactivity

reproduction

Find out more

The second kitten, who

carries two tortoiseshell

alleles, does not have a

tortoiseshell coat

because he is male.

genetics

1859 darwin publishes

his theory of evolution.

1866 Mendel establishes

laws of inheritance.

1869 Friedrich Miescher

isolates “nuclein”, later

called dnA.

1905 X and y sex

chromosomes discovered.

1910 Thomas Morgan

confirms chromosome

theory of heredity.

1927 genetic mutation

in fruit flies created

using x-rays.

1941 Proved that one

gene produces

one protein.

1944 shown that dnA

controls heredity.

1953 watson and

Crick discover the

structure of dnA.

1966 genetic code

cracked.

1984 discovery of

dnA fingerprinting.

2003 Human genome

project to identify genes,

is completed.

Female

tortoiseshell cat

Identical twins are

of the same sex

because they come

from a single

embryo.

Only one kitten is

tortoiseshell like her mother,

because she carries two

alleles and is female.

Male cat

carrying

tortoiseshell

allele

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