Download Introduction and Background to Genetic Approach File

Quantitative Genetics
ANS 512
Introduction
Purpose
Texts
By
T.N. Gondwe, PhD
Lecture 1
Course Aims
• To equip students with knowledge of
population genetics and principles
of animal breeding as applied to
livestock improvement
• To enable students to apply theory
of quantitative genetics to improve
livestock performance through
breeding in all sectors
Course outcome
• By the end of the course, students
should be able to
•demonstrate an understanding of
principles of quantitative genetics
•show an understanding of how to
apply the principles in livestock
improvement through breeding
practices
Topics of study
• Background to animal breeding
• Genetic constitution of a population, a
review
• Quantitative traits and measures of
quantitative traits
• Principles of selection
• Response to selection and its prediction
• Inbreeding and relationship
• Effect of population size on inbreeding
and genetic drift
• Crossbreeding and heterosis
Topics of study
• Practical on
• Calculation of gene and genotype
frequencies
• Performance recording including data
processing
• Estimation of heritability
• Prediction of selection response
• Computing inbreeding and crossbreeding
parameters
Texts
Prescribed
• Falconer, DS and Mackay, TCF (1996).
Introduction to Quantitative Genetics
• Wiener, G. (1994). Animal Breeding. CTA, The
Tropical Agriculturalist. Macmillan Press Ltd.,
London.
• Simm Geoff (2000). Genetic Improvement of
cattle and sheep. CABI Publishing, Wallingford,
Oxon OX10 8DE, UK
Recommended
• Legates, JE and Warwick, EJ (1990). Breeding
and improvement of farm animals
• Chapman, A.B. (Ed) 1985: General and
quantitative genetics. Elsevier, Amsterdam.
Assessment
• Course Work
40 %
• End of Course Exam 60
Topic 1: Genetic approach to
animal improvement
Aim
• To introduce to students quantitative
genetic approach to livestock
improvement
Objectives
•
Upon completion of the topic, students
should be able to
1. Recall the roles of keeping livestock
2. Discuss the need to improve animal performance
3. Explain the genetic and non-genetic
(environmental) approaches to livestock
improvement
4. Discuss advantages and disadvantages of each
approach
5. Discuss potential of genetic improvement in
developing countries
Objective of Genetic Approach
To improve animal performance through
breeding
By applying principles of genetics
Review roles of animals / livestock ~
how can you measure these roles?
Source of food (eggs, meat, milk, etc)
Animal power (draught power)
Provide organic fertilizer, chicken manure,
5 % N, 21 % Ash
Hides and skins
Income and coping against hunger
Cultural, leisure, prestige, etc.
These roles of livestock
Constitute animal performance
That is shown physically (Qualitative) or
through measurement (Quantitative)
And need to be improved
Animal performance
Is expressed as Phenotype
What we observe (e.g. hair coat) or measure (e.g.
milk yield). In general, external expression of an
animal
That constitutes
Genetic (internal factors), and
Non – Genetic (external factors) components
P
=
Phenotype
G+E
Genetic
Environment
Animal performance levels
depend on
Genotype
Housing
Climate
Sex
Age
Health
Nutrition
Management
Animal performance
Phenotype
Environment
Genotype
Basic approaches towards
improving performance
There are two
Environmental approach
Genetic approach
These can work separately but works
better when combined
Environmental approach
This works by improving the animal
environment
This exploits the E component that is non –
genetic (external factors)
You manipulate the environment to make
it more favourable for animal growth,
reproduction
P
=
G
+
E
Environmental approach involves
Climate / housing conditions
Nutrition
Health conditions
Management (handling and care of
animals)
Environmental approach
You improve animal performance
through
Good feeding (Nutrition)
Quality of feeds, frequency of feeding
Improving animal health
You prevent and control animals from
diseases and parasites
By vaccinations, prophylaxis, antibiotics,
sanitation, treatment, clean water
Environmental approach
Through growth hormones
That make animals grow
bigger
And all aspects that
enhance better
environment for the
animals
Good animals can
be produced from
good environment
Advantages of environmental
approach
Quick response is obtained
e.g., change from bad to good feeding
Results get realised within a week
Problems with environmental
approach
Improvement tend to be temporal
Once you withdraw the manipulation, performance
goes down
Such as withdrawing drugs, feeding
The potential of an animal to produce is
determined by its genetic make up
If genetic potential of zebu is 320 kg, that is the
maximum it can achieve, no matter what
environmental manipulation
~ liken to capacity of a car tank
Problems with environmental
approach
P
=
G
Limit
+
E
Problems with environmental
approach
Local and Ross
Four week old,
Intensive
At 8 wks, 2.0 kg
Eight weeks old
chicks, free range
At 8 wks, .8 kg
Problems with environmental
approach
600
Live weights (g)
500
400
300
BA
Local
200
100
0
1
2
3
4
5
6
7
8
Age (wks)
Comparing BA and Local chickens at 8 weeks,
under similar management
Genetic approach to animal
improvement
In order to change the limit of an animal,
there is need to use this approach
You manipulate the genes or genetic
makeup of an animal
This elevates the genetic potential of an
animal
With this approach, you exploit the
Genetic component
P
=
G
+
E
Genetic approach to animal
improvement
Goodness is that once you manipulate
the genes, that tend to be permanent
With this approach, the improvement is
therefore, permanent
You increase an animal potential by
concentrating desirable genes
Using various theories and means that will
be discussed in the course
Problems with genetic approach
Despite having permanent gain, the
improvement is very slow
It may take four generations for the
improvement project to be successful
This may be > 15 years in Zebu Cattle
It is shorter periods with smaller animals
Due to high and fast reproductive rates
and generation intervals
Problems with genetic approach
Despite the permanent improvement,
you also need to improve the
environment so that improved genes
could fit in and express their potential
Hence simultaneously improve feeding,
management, housing, disease control
etc.
Problems with genetic approach
Good feed
Poor feed
Problems of Genetic approach,
Malawi case
Most project in Malawi run for 4 – 5 years
And later get abandoned due to lack of
personnel, funds, proper planning of
breeding goals and programmes
There is high labour turn over in universities
and government research institutes
Hence genetic progress does not seem to
make progress
Potential of genetic improvement
in SADC
Is quite high
Through existence of indigenous breeds
That have not been exploited yet
And possess a biodiversity of genotypes
In almost all species
Different livestock improvement
approaches
Basic farm practical in feeding,
management, disease control facilitates
better environment, hence improvement
through environmental approach
Understanding genetics, keeping records
enable knowing the animal you work with
in terms of its performance, feed
consumption, reproduction, products and
this facilitates genetic improvement of
livestock