Page 9 - Reproduction in Animals

reproduction in which an animal there are other methods by which a
reproduces by dividing into two single parent reproduces young ones.
individuals is called binary fission. You will study about these in your
Apart from budding and binary fission, higher classes.

Story of Dolly, the Clone

Cloning is the production of an exact copy of a cell, any other living part, or a
complete organism. Cloning of an animal was successfully performed for the first
time by Ian Wilmut and his colleagues at the Roslin Institute in Edinburgh,
Scotland. They successfully cloned a sheep named Dolly [Fig. 6.13 (c)]. Dolly was
th
born on 5 July 1996 and was the first mammal to be cloned.

(a) Finn Dorsett sheep (b) Scottish blackface ewe (c) Dolly

Fig. 6.13
During the process of cloning Dolly, a cell was collected from the mammary gland
of a female Finn Dorsett sheep [Fig. 6.13 (a)]. Simultaneously, an egg was obtained
from a Scottish blackface ewe [Fig. 6.13 (b)]. The nucleus was removed from the
egg. Then, the nucleus of the mammary gland cell from the Finn Dorsett sheep
was inserted into the egg of the Scottish blackface ewe whose nucleus had been
removed. The egg thus produced was implanted into the Scottish blackface ewe.
Development of this egg followed normally and finally Dolly was born. Though
Dolly was given birth by the Scottish blackface ewe, it was found to be absolutely
identical to the Finn Dorsett sheep from which the nucleus was taken. Since the
nucleus from the egg of the Scottish blackface ewe was removed, Dolly did not
show any character of the Scottish blackface ewe. Dolly was a healthy clone of
the Finn Dorsett sheep and produced several offspring of her own through normal
sexual means. Unfortunately, Dolly died on 14 th February 2003 due to a certain
lung disease.
Since Dolly, several attempts have been made to produce cloned mammals.
However, many die before birth or die soon after birth. The cloned animals are
many-a-times found to be born with severe abnormalities.

74 SCIENCE

Rationalised-2023-24