Mendel

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Mendels Laws of Heredity-Why we look the way we
look...

• EQ What is the significance of Mendels
• experiments to the study of genetics?

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What is heredity?

• The passing on of characteristics (traits) from
  parents to offspring
• Genetics is the study of biological inheritance
  and variation in organisms.

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Mendel used peas...
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Mendels Pea Plants

• They reproduce sexually through self-pollination
• Have both sex organs with two distinct, male and
  female, sex cells called gametes
• Fertilization sperm egg

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Mendel crossed them

• Cross - combining gametes from parents with
  different traits
• Line of plants (offspring) became purebred,
  genetically uniform

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Genes and Alleles

• Genes - located on chromosomes, they control how
  an organism develops and looks
• Each organism has two alleles for each trait
• Alleles - different forms of the same gene

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What Did Mendel Find?

• He discovered three laws and rules that explain
  factors affecting heredity.

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1. Rule of Dominance

• The trait that is observed in the offspring is
  the dominant trait
• expressed no matter what when present
• The trait that disappears in the offspring is the
  recessive trait
• only expressed when two copies of the allele are
  present

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Rule of Dominance
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2. Law of Segregation

• Organisms inherit two copies of each gene, one
  from each parent.
• The two alleles for a trait must separate when
  gametes are formed during Meiosis
• A parent randomly passes only one allele for each
  trait to each offspring

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3. Law of Independent Assortment

• The genes for different traits are inherited
  independently of each other.

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Phenotype Genotype

• Phenotype - the way an organism looks
• red hair or brown hair
• Genotype - the gene combination of an organism
• AA or Aa or aa

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Heterozygous Homozygous

• Heterozygous - if the two alleles for a trait are
  different (Aa) (one dominant one recessive )
• Homozygous - if the two alleles for a trait are
  the same (AA or aa) (both dominant Or both
  recessive)