Introduction to Mendelian Genetics

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Introduction to Mendelian Genetics

• General Biology
• Lecture Notes

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What is inheritance?

• Money, property
• Gene
• Sequence of DNA that codes for a protein and
  determines a trait
• Genetics Study of heredity

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Gregor Mendel

• Austrian Monk
• B. 1822 in Czech Republic
• Garden Peas
• Foundation for science of genetics

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Mendels Peas

• True-Breeding if allowed to self-pollinate,
  produce offspring identical to themselves.
• One parent.

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Mendels Peas

• Cross-Pollinate Male sex cells in pollen from a
  flower on one plant fertilize the egg cells of a
  flower on another plant.
• Two parents.

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Traits

• A specific characteristic that varies from one
  individual to another.
• Ex.) Seed color, Plant height, Hair color

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Hybrids

• Offspring of crosses between parents with
  different traits.

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Genes vs. Alleles

• Genes Chemical factors that determine traits.
• Ex. Hair Color
• Alleles Different forms of a gene.
• Ex. Red, Blonde, Brown, Black

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Principle of Dominance

• Some alleles are dominant and others are
  recessive.
• Ex.) Tall pea plants vs. Short pea plants

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Dominant vs. Recessive

• Dominant An allele whose form of a trait always
  shows up in an organism if the dominant allele is
  present.
• Recessive Allele whose trait only shows up when
  the dominant allele is not present.

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Gametes

• Sex Cells
• Contain 1 Allele Each
• Segregation Separation of paired alleles

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Homozygous

• An organism with two identical alleles for a
  particular trait.

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Heterozygous

• An organism with two different alleles for the
  same trait.

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Genotype

• Genetic makeup.

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Phenotype

• Physical characteristics.

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Punnett Square

• Diagram.
• Possible gene combinations for offspring of a
  genetic cross.

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Background Info. For Practice Problems

• Bunnies
• Brown fur color Dominant (B)
• White fur color Recessive (b)
• Long Ears Dominant (L)
• Short Ears Recessive (l)
• White Whiskers Dominant (W)
• Black Whiskers Recessive (w)

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Make a Punnett Square for a Cross Between a BB
rabbit and a bb rabbit.
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Cross a Ll rabbit with a Ll rabbit.
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Cross a homozygous dominant white whiskered
rabbit with a black whiskered rabbit.
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Cross two rabbits that are both heterozygous for
brown fur.
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Genotype Ratio

• Cross two rabbits that are Ww and Ww. (White
  whiskered)
• What is the genotype ratio?

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What is the genotype ratio for a cross between
the following rabbits? Ll and ll?
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Phenotype Ratio

• Cross two rabbits that are Ww and Ww. (White
  whiskered)
• What is the phenotype ratio?

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What is the phenotype ratio for a cross between
the following rabbits? Ll and Ll
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What are the odds of having a short-eared rabbit
baby if both parents are heterozygous for
long-ears? What if one parent was short-eared?
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Pedigree