Download AG-ASB-02.421-11.1P Genetics

Genetics
Modified by Georgia
Agricultural
Education
Curriculum Office
July 2002
August 2008
Genetics
• Is the science of heredity.
• Heredity is the transmission of genetic or
physical traits from parent to offspring.
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Gregor Mendel
• Austrian Monk
• Considered the “Father of Heredity”
• He conducted plant breeding experiments
in their monastery garden.
• In 1865 he made his work public, units of
inheritance.
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What makes us unique?
• Each of the 100 Trillion cells in our body
except the red blood cells contains the entire
human genome, in the nucleus of every cell
is the genetic information “blueprint” to
construct the individual.
• It is the Deoxyribonucleic acid (DNA)
• Function of DNA
– Genetic code for almost every organism.
– Provide template for protein synthesis.
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Composition of DNA
• The structure of DNA was discovered by Watson and
Crick in 1953.
• It is a twisted double helix molecule, containing
sugar, phosphates, and nitrogenous bases.
• The sugar is deoxyribose and the phosphoric acid
molecules are always the same and provides for the
structure (side of the ladder).
• The only difference between us is the order and
arrangement of the four bases (rungs of the ladder).
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Bases of DNA
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Adenine= A
Thymine= T
Guanine= G
Cytosine= C
A always pairs with T
C always pairs with G
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Bases of RNA
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Adenine= A
Uracil= U
Guanine= G
Cytosine= C
G always pairs with C
T from the DNA = A in the RNA
A from the DNA = U in the RNA
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DNA Model
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Chromosomes
• The DNA in every cell is located in rod like
segments called chromosomes
• Chromosomes occurs in pairs in every cell
of our body except in the sperm and ovum.
• Chromosomes numbers are the same for
each specie.
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Chromosome Numbers
Species
Cattle
Swine
Sheep
Horse
Human
Chicken
Goat
Donkey
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Diploid #
60
38
54
64
46
78
60
Haploid #
30
19
27
32
23
39
30
62
31
Chromosomes
• There are 2 sex chromosomes included
in the diploid number of the
chromosomes.
• All of the other chromosomes are
referred to as autosomes.
• In mammals if the sex chromosomes
are alike, XX it results in a female.
• If the sex chromosomes are different,
XY it results in a male.
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Sex Determination
• Females contribute an X chromosome towards
the sex of their offspring.
• Males can contribute an X or a Y chromosome
toward the sex of their offspring.
• Absence of an Y chromosome results in a the
embryo developing into a female.
• Presence of an Y chromosome results in the
embryo developing into a male.
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Sex Determination
• Gametogenesis =
Formation of gametes
through meiosis.
• Male = 4 viable
spermatids
• Female = 1 viable
ovum, 3 polar bodies.
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Tell me what I am ?????
August 2008
Tell me what
I am ?????
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Cell Division
• Meiosis
– Is the form of cell division which results reducing
the chromosome number from the diploid # to the
haploid #.
– Occurs only in the sex cells, sperm and ovum.
• Mitosis
– Is the form of cell division which results in the
formation of identical daughter cells, keeps the
chromosome number constant.
– Tissue growth and repair.
– Occurs throughout the body except in the sex
cells.
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Genotype or Gamete
• Genotype contains two copies of the
gene.
– AaBB
• Gamete (sex cells) contains only one
copy of the gene.
– AB
• Determine the possible gametes of
AaBB
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– AB
aB
Gamete or Genotype
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State if its a gamete or genotype.
Aa
D
DdEeFFgg
sRtxyq
AaBBeeFF
adgEFT
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List all the possible gametes.
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From the genotype AaBb
AB
Ab
aB
ab
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Genes
• Chromosomes contains several units of
inheritance “genes”.
• Genes usually occurs in pairs, one from
each parent.
• Some traits are inherited directly from one
set of genes.
• Some traits are inherited through several
sets of genes.
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Genes
• It was presumed that we were composed
of about 100,000 genes to construct us.
• Today, research has proven that number is
a lot less than 100,000.
• Extra credit for the student that can find an
article about the current number of genes.
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Terms to know
• Homozygous- contains 2 identical genes for
the same trait, AA, BB, cc
• Heterozygous- contains 2 different genes for
the same trait, Aa, bB, Cc
• Phenotype- Outward appearance of a trait,
coat color, polled, horned.
• Genotype- Genetic classification of a gene,
AA, Aa, aa.
• Allele- Location of a gene on the
chromosome.
• F-one = First cross mating.
• F-two = Second cross mating.
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What are dominant genes?
• The gene that express itself, the powerful
and dominant gene.
• It has the power to overshadow the recessive
gene when there is complete dominance.
• Some examples are:
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White faced in cattle
Droopy ears in swine
Polled in cattle
Black coat color in Angus cattle
What are Recessive Genes?
• The gene that is overshadowed by a
dominant gene
• Recessive genes can only express
themselves in the absence of the
dominant gene
• Polled vs Horned (Pp) (pp)
• Black wool vs white (Ww) (ww)
• Dwarfism vs normal size (dd)
• Albino
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Punnet Square
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Angus- Black coat color is dominant.
BB = Homozygous Dominant and Black
Bb = Heterozygous and is black
bb = Homozygous recessive and red
A heterozygous bull is mated to 50
homozygous recessive cows.
• How many calves are black?
• How many calves are red?
• What is the genotypic and phenotypic ratios?
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Punnet Square
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B
b
b
Bb
bb
b
Bb
bb
Results
• 2 heterozygous = Bb
• 2 Homozygous
Recessive bb
• 25 Black, 25 Red
• Genotypic ratio =
0:2:2
• Phenotypic ratio =
2 Black: 2 Red
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What are Sex Linked Genes?
• Some recessive genes are attached to the X
and Y chromosomes
• Humans: Colorblindness and Baldness are
on the X chromosomes
• In Men, traits expressed anytime present
• In Women, must have two recessives to
show trait
• Children get baldness from mothers
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If Dad is bald, will you be
bald?
Y
X B
X
X
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X X
B
X X
B
X Y
X Y
Baldness is carried by the
mother
X
X B
X
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X X B
X X
Y
X BY
X Y
What if Mom is bald?
X
X B
X B
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X X B
X X B
Y
X BY
XB
Y
What is Incomplete
Dominance?
• If both genes express themselves
• Shorthorn Cattle: Red male mated to a
White female = Roan calf
• RR crossed rr = Rr
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Punnet Square
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Shorthorn Cattle
RR = Red
rr = white
Rr = roan
If a red bull (RR) is mated to a white cow
(rr), what color will the calves be?
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Shorthorn: Red X White
R
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R
r Rr
Rr
r Rr
Rr
Punnet Square
• If a red bull (RR) is mated to a roan (Rr)
cow, what color will the calves be?
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Shorthorn: Red X Roan
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R
R
R
RR
RR
r
Rr
Rr
What if Both Parents are Roan?
R
r
R
RR
Rr
r
Rr
rr
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What is a Mutation?
• Dramatically different from what is expected
genetically
• Horned calf from polled parents
• Loss of some or extra body parts
• Lethal Mutation: causes death at birth
• Sublethal Mutation: limits animals ability to
grow to maturity
• Beneficial Mutation: loss of tail in lambs
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What is Heritability?
• Chance that traits will be inherited
• Low: multiple births, fat covering
• Medium: birth wt, wean wt, milk, wool
grade, carcass wt, rate of gain
• High: Loin eye area, fleece length &
quality
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Mating Systems
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Upgrading: mating purebreds with grade animals
Inbreeding: mating closely related animals
Linebreeding: mating distantly related animals
Outcrossing: mating unrelated animals in the
same breed.
• Crossbreeding: mating animals of same species
but different breeds.
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What is Hybrid Vigor?
Heterosis
• Offspring will outperform either of the
parents
• Corn Breed A yields 100 bu/acre
• Corn Breed B yields 100 bu/acre
• Crossbreed A & B yields corn that yields
200 bu/acre
• Vigor only expressed in crossbreeding
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The End
August 2008