Download Animal Science Genetics

Animal Science Genetics
Competency 18.01: Describe the cell and processes
involved in cell division including how genes affect the
transmission of characteristics
Competency 18.02: Discuss heritability estimates for
beef and swine
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Genetics is the science of heredity and
variation

It is the science that deals with the
differences and similarities among related
individuals


A genotype is the inheritable information
that is carried by an animal
In agricultural systems manipulation of
genetic makeup has been done to improve
productivity and increase efficiency

Gregor Mendel


Considered the father of genetics
Did an experiment with pea plants where he
discovered there were crosses between tall
and short plants helping him discover
heritability through dominant and recessive
traits.
Different Principles of Genetics

Principle of Dominance


Deals with heterozygote, one allele may conceal the presence of another
one
Principle of Segregation

Deals with a heterozygote, two different alleles segregate from each other
during the formation of gametes
 There are four main concepts related to this principle. They are as
follows:

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A gene can exist in more than one form.
Organisms inherit two alleles for each trait.
When gametes are produced (by meiosis), allele pairs separate leaving
each cell with a single allele for each trait.
When the two alleles of a pair are different, one is dominant and the
other is recessive.
Principle of Independent Assortment

Deals with alleles of different genes segregating independently of each
other

For example, a plant that had green pod color and yellow seed
color was cross-pollinated with a plant that had yellow pod
color and green seeds. In this cross, the traits for green pod
color (GG) and yellow seed color (YY) are dominant. Yellow
pod color (gg) and green seed color (yy) are recessive. The
resulting offspring (Figure A) or F1 generation were all
heterozygous for green pod color and yellow seeds (GgYy).

Cells have multiple parts

Genetic material of cells can be found in the
nucleus
Genotype vs. Phenotype

Phenotype


The observable properties of an animal
Genotype

The inheritable information carried by an
animal

Different environmental conditions or influences
from their surroundings can cause animals with
the same genotype to appear differently
Cells

The body is made up of millions of cells
that can be only seen by a microscope

The most important part of any cell is the
nucleus
Chromosomes are found in the nucleus, they are
dark-staining, rod-like or rounded bodies in the
nucleus that occur in pairs
 Chromosomes are made up of tightly coiled
strands of DNA

Genes

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A gene is made up of a specific functional
sequence of nucleotides
The collection of genes that an organism
has is called its genome
Chromosomes in the body occur in pairs,
these are called homologous pairs

Gametes are reproductive cells that do not
have paired chromosomes are referred to as
haploid

Paired would be referred to as diploid
In order for animals to grow,
cells must divide and
increase in number

Cell Division


The type of cell division in which the
genetic material of the parent cell is
duplicated and then divides into two
separate cells is called mitosis
The process of cell division that occurs in
reproductive cells is meiosis and that
ensures that the gametes only receive ½
the number of chromosomes


Gametes from one individual join with
another gamete of the opposite sex during
fertilization
All animals originate from the female’s
ovum or egg which is fertilized by the
male spermatozoa and becomes a zygote

The zygote will have a full set of
chromosomes with ½ from the male and ½
from the female

The first generation is known as the
parent or P

The offspring are referred to as the F1
generation

Their offspring are referred to as the F2 generation

And so on…

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A capital letter is used to denote a
dominant form of a gene
A lowercase letter represents a recessive
form of a gene

Example: D – drooped dominant ears in pigs,
while d – erect recessive ears in pigs
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When both genes in a pair take on the
same form they are called: homozygous

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Example: DD or dd
If they are both dominant this is called
homozygous dominant and if they are both
recessive this is called homozygous recessive

A gene pair that has one dominant and
one recessive is called:

Heterozygous dominant for that trait

Example Dd – D=drooped ears so this animal will
have drooped ears since D is dominant over d
(erect ears)
Punnett Square

A Punnett Square can be used to
determine the possible outcomes for
breeding livestock

Example I have a sow that is homozygous
recessive for drooped ears and one that is
heterozygous dominant
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dd x Dd
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So we know what dominance is …
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What is codominance?
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This occurs when one trait doesn’t completely
dominate another trait
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Example: The color Roan in horses is an example of
codominance… If a mare that is homozygous dominant
white (WW) mates with a homozygous dominant red
stallion (RR) you will get RW as your cross
 So what really happens is the horse has both red
AND white hairs, not pinkish color like many people
think
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What is epistasis?
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One or more gene can control a single trait

An allele of one of them may have an overriding
effect on the phenotype
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Example: Comb shape in chickens
 Chickens can have four different combs: walnut,
rose, pea, single
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Mutations
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Are responsible for variations in color, size,
shape, behavior, and other traits
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Mutations can occur the following ways
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Nondisjunction – change in chromosome number
Translocation/deletion – chromosome breakage
Inversion - rearrangement of genes on a chromosome
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What are sex-linked traits?

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Traits that are carried on the X or Y
chromosomes (which are involved in
determining the sex of the animal)
XX – female
XY – male

Sex-linked traits are often recessive and are
covered up in the female mammal by dominant
genes
Improvements in Breeding?
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Improvements in breeds of animals can be
done: naturally or artificially


Natural occurs in the wild or without plan of
humans
Artificial is planned and controlled by humans

Selection is done to improve breeding
stock

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The goal of selection is to increase the
frequency of animals with optimal levels of
performance
Culling aims to reduce frequency of
individuals with poor performance

(culling is the process of weeding out poor
individuals)
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Two breeding methods
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Single trait selection
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Aim at improving one trait in a breeding program
Multiple Trait selection
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Simultaneously improve multiple traits in a
program
Types of Modern Genetics and
Artificial Genetics
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Gene Transfer
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Embryonic Cloning
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Chemical or surgical splitting of developing embryos shortly after
fertilization and developing two identical offspring
Nuclear Transfer
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Transferring a gene from one individual to another
Microsurgical collection of cells from the outer layer of a
developing embryo and transferring them into an unfertilized
ovum that has had its own nucleus removed
Nuclear Fusion
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Involves the union of nuclei from two gametes