Download Selective Breeding Introduction

Selective Breeding
• Definition
• Selective breeding is also known as artificial selection.
Humans select desirable traits in a species and choose
which individuals breed in order to increase these traits in
the species.
• All crops and domesticated animals today are a product of
selective breeding.
Selective breeding vs. natural selection
• Natural selection is when certain individuals of a species are
“fitter”; they possess alleles which make them more
successful in their environment. These individuals survive
longer and produce more offspring. Therefore, more of their
alleles are passed on to the next generation and over time
these alleles become more common in the gene pool
• In selective breeding humans determine which phenotypes,
and therefore genotypes are desirable in the species. They
then increase the alleles for these traits through breeding
programs. Often the species produced would be unable to
survive in the wild
Selective breeding – nothing new
• Agriculture began 10,000yrs ago. Humans selected wild
varieties of plants and animals with the traits they desired
and began selective breeding to increase these desired traits;
e.g. to produce bigger, easier to harvest grains with a greater
yield
• Selective breeding was also used to domesticate animals.
Humans killed animals that were aggressive or not
cooperative and the only animals left to breed were the ones
most docile and easy to handle. Over time this produced
“domesticated” animals from wild ones. (Ex. Wolves  Dogs)
From Biozone powerpoint ‘cultural evolution’
Selective breeding animals
• Belgium Blue cattle – cattle bred to produce a huge amount
of muscle (meat). Produced by selecting individuals with a
mutation in myostatin gene which results in the production of
an increased number of muscle fibers (hyperplasia)
• Excess muscle growth begins in utero so calves have to be
born by Caesarean section.
• Fertilization is almost always by artificial insemination,
meaning that sperm can be shipped across continents and
only the ‘best’ bulls are selected to breed.
Selective breeding -methods
• Inbreeding is reproduction from the mating of parents who
are closely related genetically.
• Livestock breeders often practice controlled breeding to
eliminate undesirable characteristics within a population,
which is also coupled with culling (slaughtering) of what is
considered unfit offspring, especially when trying to establish
a new and desirable trait in the stock.
• Repeated test crosses are often used in order to produce
pure breeding individuals
Modern corn
Ancient corn
from Peru
(~4000 yrs old)
Choosing only the best corn plants for seeds results
in better crops over a long time.
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Selective breeding - examples
• Genome analysis of kiwifruit is being used to selectively breed
new, trademarked varieties of fruit with characteristics such
as disease resistance.
Source: http://www.plantandfood.co.nz/page/our-research/breedinggenomics/
• Sheep in NZ are being selectively bred to be immune to facial
eczema, a fungal disease that can destroy whole flocks.
Genome analysis of sheep was carried out and individuals
immune to the disease were selected for a breeding program.
Source:Ag research NZ
Other Applications of Selective
breeding
• Breeding programs for endangered species, may involve
selection of the least genetically related individuals to breed
(to maintain genetic diversity in the species).
• Selective breeding programs have resulted in higher yields
and better disease resistance in aquaculture species, such as
salmon.
Implications of selective breeding
• We are concerned with the biological implications of
selective breeding that may negatively affect :
1. Ecosystems
2. Genetic biodiversity
3. Health or survival of individuals
4. Survival of populations
5. Evolution of populations
Brainstorm some possible (general) implications of
selective breeding for each of these.