Traits and Inheritance

1
Traits and Inheritance

• 5.2

2
Objectives

• Explain how genes and alleles are related to
  genotype and phenotype
• Use the information in a Punnett square
• Explain how probability can be used to predict
  possible genotypes in offspring
• Describe three exceptions to Mendels observations

3
Terms

• Gene
• Allele
• Phenotype
• Genotype
• Probability

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A Great Idea

• GENE one set of instructions for an inherited
  trait
• Each parent gives one set to their offspring
• ALLELE one of the alternative forms of a gene
  that governs a characteristic (hair color)
• One from each parent in different forms (Dominant
  and recessive)
• Dominant capital letters (R)
• Recessive lower case letters (r)

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Phenotype

• An organisms appearance or other detectable
  characteristic
• What you see (blue eyes, brown eyes)

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Genotype

• The entire genetic makeup of an organism also
  the combination of genes for one or more specific
  traits
• Flowers- purple (P) white (p)
• 2 dominant (PP) or 2 recessive (pp) HOMOZYGOUS
• True Breeding
• One dominant and one recessive (Pp) HETEROZYGOUS

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Punnett Squares

• Used to organize information
• SEE HANDOUT
• PP (purple flower) X pp (white flower)
• All of the offspring have a genotype of Pp
• Phenotype purple
• Heterozygous purple

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• Pp (purple) X Pp (purple)
• Outcome
• PP (homozygous purple)
• 2 Pp (heterozygous purple)
• pp (homozygous white)
• Ratio 3 1

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Probability

• The likelihood that a possible future event will
  occur in any given instance of the event
• Genotype Probability
• Pp X Pp (50 chance of receiving either allele
  from parent)
• 2 p ½ x ½ ¼ (25)
• 2 P ½ x ½ ¼ (25)
• 1 P 1p 2/4 50

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Exceptions to Mendels Experiments

• INCOMPLETE DOMINANCE Each allele has its own
  degree of influence (blend together)
• OUTCOME
• R1R1(red) x R2R2 (white)
• 4 R1R2 (pink)