Transcript Genetics in Agricultural Breeding Programs

Genetics in Agricultural
Breeding Programs
Natural Selection
• Mechanism for evolution in natural
populations
• Organisms with best traits suited to the
environmental factors affecting a population
are most likely to survive and reproduce.
– Results in the inheritance of the same well-suited
traits
• Important traits in natural selection-disease
resistance, size, color pattern/camouflage,
etc.
Natural Selection
• Types of Natural Selection
– Stabilizing selection
– Directional selection
– Disruptive selection
Stabilizing Selection
• Individuals with the average or norm for a
trait have an advantage over other forms of
the trait
– Example: gray moths (norm) are favored over
black and white moths
Directional Selection
• Individuals with one extreme or less
common version of a trait are favored over
other forms of the trait.
– Example: Black moths are favored over gray or
white moths
Disruptive Selection
• Multiple extremes or alternative forms of a
trait are favored over the norm
– Example: Black moths and white moths are
favored over gray moths
Selective Breeding
• Method of breeding plants and animals
utilized in agriscience to produce offspring
that possess certain characteristics
desirable to agriculturists
– Utilized for generations-produced the first domestic
animals in early civilizations
Selective Breeding
• Used to select for a variety of traits
including:
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Muscling/Size
Fat content
Breeding Capability
Color
Speed/Agility
Temperament
Milk Production
Selective Breeding
• Methods for selective breeding:
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Artificial insemination
Pen/field breeding
Isolation Breeding-inbreeding
Mechanical pollination of plants
Hybridization of plants and animals
Selective Breeding
• Selective breeding is accomplished much
quicker in plants than animals due to
growth rates and ease of
propagation/production
Selective Breeding
Techniques
Objective: Summarize the pro
and purpose of selective bree
techniques
Techniques in Animals
• Progeny testing is used to determine the
value of male livestock by analyzing the
transmission of traits to offspring and its
breeding potential
• Artificial insemination has proven to have
the greatest impact on animal breeding
since the first domestication of livestock.
Artificial Insemination
• Semen is collected from male individuals – methods vary
widely by the type of animal
– Artificial vaginas are used for larger mammals.
• Semen is checked for viability and flash frozen in
specialized straws.
– Straws should be placed in storage tanks filled with liquid
nitrogen, till use.
– Semen stored under proper conditions has proven viable
decades later (-320ºF)
– Female is treated with prostaglandin (hormone) to induce
estrus or heat
– Semen straws are immediately thawed in water (99ºF) and
soon after inserted into the mother using a specialized
release gun.
Sperm Sexing
• Utilizes a cytometer cell sorter to separate
male sperm from female sperm
– Sperm with X chromosomes (female sperm) weigh
more (contain more DNA) than those with a Y and
can thus be dyed and separated because they
absorb more dye
Invitro-Fertilization
• Method of removing eggs from a mother for
fertilization under laboratory conditions.
– A large number of eggs are collected from the
ovaries of an outstanding female and fertilized in
Petri dishes under laboratory conditions
– Embryos can be inserted into surrogate mothers or
frozen for later use
– Offers the most control and requires the least
amount of semen.
Birth Through Surrogate Mothers
• Hormones are used to cause the female to
superovulate (produce a large number of
eggs).
• Original mother undergoes artificial
insemination
• Fertilized eggs are removed by a process
called FLUSHING to be placed in other
female animals for development.
Cross-Pollination in Plants
• Method used to select particular parents for the
production of seed in plants.
• Process
– Plants possessing desirable characteristics are
selected and carefully monitored
– Pollen can be gathered from male plants (or
flowers) months or in some cases, years in
advance and refrigerated for storage
– Flowers on the female part must be covered prior to
opening, and if capable of self-pollination, must
have the stamens removed.
– Once the female flowers open, pollen from the male
should be placed on the stigma, and the flower
covered again.
• Record keeping is critical in crossing plants.
Selecting Plants and
Animals for Breeding
Observe Patterns of Heredity
• The occurrence of genetic disorders in
offspring or parents is an indicator that the
parent may have a recessive gene for the
disorder
• Though genetic recombination is random,
some animals are more likely to transmit
genes than others
• Keeping careful breeding records improves
effectiveness
Select Animals Carefully
• Along with a good genetic background,
animals used in selective breeding should
be:
– Healthy-old injuries or illnesses are not a factor
unless they are a result of genetic propensities or
impair breeding capabilities
– Carefully monitored-nutrition levels, pests and
stress can all reduce breeding viability. Some very
good specimens are completely isolated.
Select Animals Carefully
• Hybrids should be avoided, since traits
expressed in the organism are rarely
transmitted to offspring
– The process of inbreeding isolates genes for only a
single generation, as many are recessive.
Carefully Plan Breeding Crosses
• Plants can be crossed not only within
species (interspecific), but also within
genus (intergeneric), and even, in rate
cases family (interfamilial)
• Animals are usually limited to crosses
within the same species
Methods for Producing
Selective Breeding
Programs
Inbreeding
• Crossing organisms that are genetically
related
– Crossing two plants to produce an f1 generation,
then crossing two of the f1 offspring to create an f2
generation
Backcrossing
• Crossing offspring from a cross with one of
the previous parents, or a similar organism,
to maximize the expression of certain traits.
– Often used after intergeneric crosses to produce
offspring that possess more characteristics from
one genus.