Download Genetics 1

Genetics
Chapter 4
Genetics
• Is the science of heredity.
• Heredity is the transmission of genetic
or physical traits from parent to
offspring.
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.
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.
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).
Bases of DNA
• Adenine= A
• Thymine= T
• Guanine= G
• Cytosine= C
• A always pairs with T
• C always pairs with G
Bases of RNA
• 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
DNA Model
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.
Chromosome Numbers
Specie
Cattle
Swine
Sheep
Horse
Human
Chicken
Goat
Donkey
Diploid #
60
38
54
64
46
78
60
62
Haploid #
30
19
27
32
23
39
30
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.
Sex Determination
• Female can contribute only a X chromosome
towards the sex of their offspring.
• Male 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.
Sex Determination
• Gametogenesis =
Formation of
gametes through
meiosis.
• Male = 4 viable
spermatids
• Female = 1 viable
ovum, 3 polar
bodies.
Tell me what I am ?????
Tell me what I am ?????
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.
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
– AB
aB
Gamete or Genotype
• State if its a gamete or genotype.
• Aa
•D
• DdEeFFgg
• sRtxyq
• AaBBeeFF
• adgEFT
List all the possible gametes.
• From the genotype AaBb
• AB
• Ab
• aB
• ab
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.
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.
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.
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:
–
–
–
–
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
Punnet Square
•
•
•
•
•
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?
Punnet Square
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
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
If Dad is bald, will you be
bald?
Y
X B
X
X
XX
B
XX
B
X Y
XY
Baldness is carried by the
mother
X
X B
X
X X B
X X
Y
X BY
X Y
What if Mom is bald?
X
X B
X B
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
Punnet Square
• 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?
Shorthorn: Red X White
R
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?
Shorthorn: Red X Roan
R
R
R
RR
RR
r
Rr
Rr
What if Both Parents are
Roan?
R
r
R
RR
Rr
r
Rr
rr
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
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
Mating Systems
• 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.
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
The End
• You can use your notes to do the next
two worksheets.