Genetics

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Genetics

• Modified by Christina Wooden
• Credit Given Georgia Agricultural Education
• Curriculum Office
• July 2002

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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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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 Diploid Haploid
• Cattle 60 30
• Swine 38 19
• Sheep 54 27
• Horse 64 32
• Human 46 23
• Chicken 78 39
• Goat 60 30
• Donkey 62 31

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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 ?????
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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
• AB aB

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Gamete or Genotype

• State if its a gamete or genotype.
• Aa
• D
• DdEeFFgg
• sRtxyq
• AaBBeeFF
• adgEFT

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List all the possible gametes.

• 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
• White faced in cattle
• Droopy ears in swine
• Polled in cattle
• Black coat color in Angus cattle

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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

• 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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Results

• 2 heterozygous Bb
• 2 Homozygous Recessive bb
• 25 Black, 25 Red
• Genotypic ratio 022
• 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?
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Baldness is carried by the mother
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What if Mom is bald?
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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?

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Shorthorn Red X White
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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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What if Both Parents are Roan?
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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

• 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