Uploaded by moira kennedy

Lesson 7 - Selective Breeding

Why do we selectively
breed animals?
Success Criteria
• State what selective breeding is
• Explain why domestic and farm animals
have been bred to give desirable
• Describe why selective breeding does
not always produce desired results
What is selective breeding?
• Selective breeding is when people chose
the individuals to breed together to
produce new varieties of a species
A variety is a type of a particular species
that is different in some clear way from
other varieties of that species
What is selective breeding?
For example, pedigree dogs come in lots of
different varieties, called breeds of dog.
They may be different colours and sizes, but
they are all still dogs
They are all still the same species
Different varieties of dog have been produced
by selective breeding
Why are Cows selectively breed?
Selective breeding permits the encouragement of
characteristics that are more beneficial to the
• If you have livestock like cows, it can produce more
milk than typical cows, when you breed them, the cow
will produce more milk and this gene can be passes to
their offspring.
• Promoting these advantages (methods) will surely
increase the market value of these products
• If you are a businessman, using selective breeding is
undeniably a perfect option
Selective Breeding of Cows
Selective breeding of cows
• Suppose you wanted a variety of cow that produced a
lot of milk
This is what you could do:
• Choose or select the cows in your herd that produce
the most milk
• Let only these cows reproduce
• Select the offspring that produce the most milk
• Let only these offspring reproduce
• Keep repeating the process of selection and breeding
until you achieve your goal
Other examples of Selective Breeding
Other examples of selective breeding
The key here is to identify the feature you want, and
only breed from the individuals that have that
Here are some examples of what selective breeding can
• Hens that lay big eggs of a particular colour
• Cattle that produce lots of meat
• Tomato plants that produce lots of tomatoes
• Crops that are resistant to certain plant diseases.
Is selectively breeding always good?
Selective breeding has advantages, but it also has
Loss of Variety
• Selective breeding usually requires inbreeding of plants and
• As a result, it causes the genetic variety to decrease
• As the genetic variety is reduced, the organisms may express
same vulnerability to certain pathogens
• In case a group of plants or animals with the same traits or
genes are attacked by a particular pathogen the entire
population of these plants and animals will certainly suffer
Is selectively breeding always good?
Animal Discomfort
• Breeders who want to formulate particular traits like
to produce large quantity of milk, it may accidentally
reproduce traits that are damaging to the health of
the animal
• For example, cows can only produce large amount of
milk if they have large udders
Does Selective Breeding always work?
• Selective breeding does not always
produce desirable characteristics
• This is because fertilisation is a random
process which involves the element of
1. What is selective breeding?
2. Explain how cows are selectively breed
3. Explain why selective breeding does
not always produce desirable