methods of breeding

8/14/2019 Methods of Breeding

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Breeding Systems

A breeding system is basically the means by which animals mate

There are numerous systems used by both nature and man to produce offspring

In research, our main focus is on the genes involved in breeding

Selective Breeding

Gene Technology


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Breeding SystemsSelective Breeding

Used by humans for centuries, initially starting to improve food resources

The vast majority of the plants and animals we use today have been cultivated (selected)

on the basis of some phenotype e.g. faster growing, more abundant yield, better colour

Commonly used in cattle, sheep, horses, dogs, cats

Sires and dames chosen for selected characteristics


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http://learn.genetics.utah.edu/content/variation/artificial/
http://learn.genetics.utah.edu/content/variation/artificial/http://learn.genetics.utah.edu/content/variation/artificial/


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The rate of change (improvement) of a particular characteristic depends on three factors:

1the heritability of the characteristic

2the superiority (strength) of the particular character in the chosen stock

3the environmentthe animal is maintained in i.e genetic potential will not be reached if

the environment is unsuitable

Different breeding strategies are used in selective breeding:

Random breeding

Inreeding

Line Breeding

Outbreeding


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Random Breeding

Where an organism is equally likely to mate with any other individuals in a population

Generally unplanned

Puppy mills do a form of selective random breeding looking more for sellability of

puppies e.g. small white fluffiesno real emphasis on selecting for robust offspring,

backyard breeders are often similar.


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Inbreeding

Breeding closely related animals e.g. brother/sister

Used to ensure animals breed true i.e. increase the number of homozygous gene loci,

resulting in more phenotypically uniform offspring

Used commonly in research to ensure uniformity in the line

Lines are considered inbred after mating brother and sister for 20 or more generations

Genetic testing is use to confirm uniformity

This is then called a pedigree line


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Effects of Inbreeding

Inbreeding depression = reduced fitness in a given populationa result of breeding

related individuals; results in population bottleneck

Appearance of recessive mutations

Decrease in litter size/productivity

Increased susceptibility to disease

Higher Mortality

Therefore: important to select animals with maximum productivity and health


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Catalyst Program discussing Pedigree Dogs Exposed

http://www.abc.net.au/catalyst/stories/2688984.htm

Pedigree Dogs
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Outbreeding

Mating animals that are unrelated

Heterosis (Hybrid Vigor) = when a hybrid is seen to be superior to its parents

Over a series of generations genetic diversity is maintained, rotating material throughout

the colony.

Inbreeding kept to a minimum

The success of this system is dependent on:

-The diversity of the groups in the first place

-The speed with which each generation is replaced i.e. the slower the better-The equal representation of females and males from each group


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OutbreedingPoiley System

Offspring Gene Mix


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Gene Technology

With the current knowledge of genetics, we can further manipulate the genetics of the

offspring

GMOs = one in which the genes are altered by man

-Definition = those in which the genetic material is altered in a way that does not occur

naturally by mating or natural recombination

-Organism is genetically modified using recombinant DNA technologies, or genetic

engineering

-In GMOs, genes are either deleted, inserted or altered in some way e.g. enhanced or

dampened


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Gene Technology

GMO Example

Knockout Micespecific genes have been rendered non-functionalknocked out in

order to study their effect

Recombinant Gene Technology

Combines DNA from different sources with the genome of an

organism

Creates different/new phenotypes (protein products) by expression

of the inserted DNA


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Gene Technology

Transgenic Animal

Carries a foreign gene that has been deliberately inserted into its genome


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http://learn.genetics.utah.edu/content/tech/t

ransgenic/

Laboratory Breeding Aims

How to build a transgenic mouse
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Laboratory Breeding Aims

In the research setting, animals are bred predominantly for:

Producing research animals

Maintaining a breeding colony

Animals required for research may be:

Outbreed

Inbreed


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LaboratoryOutbred Colonies

Hartley Guinea Pig

Albino Guinea Pig

Specific stock are often designated by the lab that develop them and the strain name

e.g. Crl:Ha = Charles River laboratories, Hartley

New Zealand White Rabbit

Originally bred for meat and fur

Also popular pets


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Rats

Asmu:SD (animal services, Monash

University: Sprague Dawley)

Mice

Swiss Mice


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Some breeding colonies are maintained for behavioural research, such as wildlife, monkey

etc.

Hence these are more natural form, although some species more uniform than their wild

counterparts (due to limited genetic stock)


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LaboratoryInbred Colonies

Most commonly used for rodents

Animals are bred brother to sister for 20 generations

The resulting animals are considered strains

Can be traced back to a single ancestral pair at 20thgeneration

98.6% homozygous

Genes essentially identicalisogenic (same genes)

e.g. C57BL, CBA, DBA, BALB


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Mating Systems

A mating system refers to the way in which we group animals to breed.

Mating systems can vary between institutions or within the same institute depending on

the purpose of breeding

Common mating systems you will encounter include: paired (monogamous), timed, trio,

polygamous, harem


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Mating SystemsPair Mating

Used commonly in mice and rats

Stable long-term pairs of one male and female in a single cage

Usually in a standard mouse cage, male and female left in cage together continuously

Females are not removed from the cage for delivery

Co-parenting

Post-partum oestrus (within 24 hours of parturition) is utilised


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Mating SystemsPair Mating

Advantages

Decreased time interval between litters

Maximised female production

Easy management as female is not closely monitored for removal prior to parturition

Disadvantages

Requires more males

More physically demanding for females, therefore they may require culling at an earlier

time point


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Mating SystemsTimed Mating

Manually placing female(s) with a male for a short interval (i.e. overnight, or till mating

observed)

Also called hand mating

Used commonly in rabbits, dogs and cats

Advantages

Provide precise estimation of time of mating

Provides method for timed deliveries

Less males required

Disadvantages

Time consuming

Labour intensive

More females


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Mating SystemsTrio MatingA breeding system that employs a single male and two females in one cage

If a standard cage is used one female should be removed when obviously pregnant to

reduce overcrowding when both females give birth

Alternatively, the trio can be placed in a larger breeding cage that can accommodate three

adult mice and two litters


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Mating SystemsTrio MatingAdvantages

Requires relatively few males (compared to paired mating)

Can expand a line in a short period of time

Disadvantages

Can be time consuming/labour intensive if using standard caging

May be physically draining (stressful) on females to continually produce litters without a

rest period between litters


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Mating SystemsPolygamous Mating

Polygamous mating system involves using one male to more than two females, usually up

to 4-6

The females are removed as they become pregnant (visibly)

Advantages

Uses less males than pair and trio mating systems

Relatively quick way to produce offspring

Disadvantages

Can be labour intensive in terms of pregnancy detection and removal of females


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Mating SystemsHarem Mating

Similar to polygamous mating, however the females are not removed prior to parturition

Generates the most offspring per male mouse

One male with typically 3-4 females and not exceeding 7 females

Commonly used with guinea pigs, mice

Advantages

Requires relatively few males

Can expand a given strain in a short period of time

Disadvantages

Requires a system for identifying individual females

Management can be difficult i.e. tracking litters

methods of breeding

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