DNA

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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

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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?

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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.

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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?

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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.

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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.

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Dominant vs. RecessiveAngus Cattle
Which is which, you tell me!
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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?

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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).

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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).

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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

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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?

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• 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.
•  

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Heres how we set it up...
B
b
B
b
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Heres 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".

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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.

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Use the Punnett Square

• a. Let's say a cow has the genotype "BbPp" ("B"
  black, "b" red, "P" polled, and "p"
  horned).
• The bull has the genotype "BbPp" also
• If we breed these two, what are the genotypic
  percentages of the offspring?

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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

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Lets work this out...
Bp BP bp bP
Bp
BP
bp
bP
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• We can determine the percentages of the various
  genotypes by adding up similar genotypes.
• What are all the possible genotypes?

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• "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

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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

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Sources

• California Ag Ed Tech Prep
• Scientific Farm Animal Production An
  Introduction to Animal Science