DNA
Jurassic Park Clip
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What is the
difference?
Mitosis vs Meiosis
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Mitosis
Mitosis is how somatic--or non-reproductive cells--divide.
Somatic cells make up most of your body's tissues and
organs, including skin, muscles, lungs, gut, and hair cells.
In mitosis, the important thing to remember is that the
daughter cells each have the same chromosomes and
DNA as the parent cell.
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Meiosis
Meiosis is cell division that creates sex cells, like female egg
cells or male sperm cells.
Meiosis is why we have genetic diversity in all sexually
reproducing organisms.
Genetic recombination is the reason full siblings made from egg
and sperm cells from the same two parents can look very different
from one another.
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Meiosis
• Is the reason we study genetics.
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Livestock Breeding and
Genetics
Dominant and Recessive Genes
Objectives for this Lesson:
• Determine who Gregor Mendel is and what
he did.
• What does “dominant” mean and “recessive”
and provide an example of this with livestock.
• What do we mean by genotype and
phenotype?
• What are the differences between
heterozygous and homozygous?
• How do we complete Punnett Squares? With
one trait? Two traits?
Mendel and Genetics
• Monk
• Discovered what
inheritance is.
• Discovered dominant
and recessive traits
through experiments
with pea plants
• His work allows us to
understand how genes
determine traits in
livestock and other
creatures.
Qualitative Traits
Dominant and recessive traits are traits controlled by 1 pair
of genes, and are referred to as QUALITATIVE TRAITS.
Some examples include:
1) coat color in Angus cattle
2) polled or horned trait in cattle
3) white color in swine
4 ) white wool in sheep
So what is meant by the term dominant?
Define DOMINANT
DOMINANT : when one gene completely
masks the effect of the other.
For example:
• The black coat color is dominant over red
coat color in Angus cattle.
How is Dominant Indicated?
• The dominant trait is indicated by a capital
letter, such as "B" for the black coat color.
• The degree of dominance depends upon the
animal's entire genetic makeup together with
the environment to which it is exposed.
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Define Recessive!
RECESSIVE: when a gene will not show its
effects if there is a dominant gene present.
For example:
• The red coat color is recessive in Angus cattle.
• Recessive is Represented with:
• a lower case letter, such as "b" for red coat
color.
Dominant vs. Recessive
Angus Cattle
Which is which, you tell
me!
Genotype
Moving on to genotypes:
• The genetic makeup of an organism or
group of organisms with reference to a
single trait, set of traits, or an entire
complex of traits.
• This will be represented with Letters!
What are the categories of genotypes?
Phenotype
• This refers to the physical characteristic of
the animal.
• Notice both Phenotype and Physical start
with P!
• This is what we see in the animal, such as
color.
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Homozygous = SAME
HOMOZYGOUS means that the gene on each
chromosome in the pair codes for the same
variation of the trait. For example:
• A cow that is homozygous for black coat
color could be indicated by a genotype of
"BB".
• If she is red, her genotype must be "bb",
since red color is recessive (this only occurs
when there are no dominant genes present).
Heterozygous = Different
HETEROZYGOUS means that the two alleles at a
gene locus are different; each codes for one of
the variations of the trait.
For example:
•
A cow that is heterozygous for black coat color
could be indicated by a genotype of "Bb".
• The black gene is the dominant one and is
displayed phenotypically (physically).
Punnett Square! The fun part!
• Now we move on to the Punnett Square:
This may be used to determine the
percentage of offspring that will show
each variation of the trait.
For example…
Scenario: Monohybrid Cross
A black cow with the genotype "Bb" is bred
to a black bull with the genotype "Bb".
What will be the percentage of calves
having each possible genotype?
The bull produces sperm carrying 50 percent
"B" genes and 50 percent "b" genes, the
cow has the same percent of eggs - 50
percent "b" and 50 percent "B" genes.
So in the problem, each animal is represented
with Bb.
Here’s how we set it up...
B
b
B
b
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Here’s how we set it up...
B
b
B
BB
Bb
b
Bb
bb
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Genotype
• 25 percent "BB"
• 25 percent "bb"
• 50 percent "Bb".
Phenotype
• 25 percent red
• and 75 percent black since "Bb" and
"BB" have the same phenotype.
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Dihybrid Cross
• This refers to crosses using two separate
traits. For example:
a. The polled trait "P" and black coat color
"B" will be used to demonstrate the
dihybrid cross.
b. Remember that GENES DETERMINING
THESE DIFFERENT TRAITS ARE
TRANSMITTED INDEPENDENTLY.
Use the Punnett Square
a. Let's say a cow has the genotype "BbPp"
("B" = black, "b"= red, "P" = polled, and "p"
= horned).
b.The bull has the genotype "BbPp" also
If we breed these two, what are the
genotypic percentages of the
offspring?
Steps of Action
1) First, determine which genotypes would be
present in the eggs and sperm as they will be
the same for both the cow and the bull.
2) "Bp", "BP", "bp", and "bP" are the possible
genotypes.
3) Next, draw a square and put the genotypes
for the cow down the side of the square and
the genotypes for the bull across the top of
the square
Lets work this out...
Bp
Bp
BP
bp
bP
BP
bp
bP
• We can determine the percentages of the
various genotypes by adding up similar
genotypes.
• What are all the possible
genotypes?
•
•
•
•
•
•
•
•
•
"BBpp" = 1/16
"bbPp" = 2/16 (1/8)
"BBPp" = 2/16 (1/8)
"BBPP" = 1/16
"Bbpp" = 2/16 (1/8)
"BbPP" = 2/16 (1/8)
"BbPp" = 4/16 (1/4)
"bbpp" = 1/16
"bbPP" = 1/16
What are the possible
phenotypes?
•
•
•
•
Black and polled = 9/16
Red and polled = 3/16
Red and horned = 1/16
Black and horned = 3/16
Sources
• California Ag Ed Tech Prep
• Scientific Farm Animal Production: An
Introduction to Animal Science