Genetic Crosses

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SECTION 11.2

• Genetic Crosses

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I. Genotype and Phenotype

• Genotype genetic makeup of an organism
• Alleles that give the organism its traits
• EX Tall Short
• Phenotype physical characteristics shown because
  of genotype
• EX

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I. Genotype and Phenotype

• Homozygous alleles that are the same for a
  characteristic
• EX Tall Short
• Heterozygous alleles that are different for the
  same characteristic
• EX Tall

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II. Probability

• Probability the chance of a specific trait occur
  or not occurring in an organism
• Probability of times trait is expected to
  happen of opportunities for an
  trait to happen
• Example
• Tall peas 150
• Short peas 50

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III. Monohybrid Crosses

• Monohybrid crossing one trait from two different
  organisms
• Use a Punnett Square
• Possible Crosses
• Homozygous x Homozygous
• Homozygous x Heterozygous
• Heterozygous x Heterozygous

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a. Homozygous vs. Homozygous

• Ex Flower Color Dominant Purple
• Recessive White

Genotype Phenotype


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b. Homozygous vs. Heterozygous

• Ex Flower Color Dominant Purple
• Recessive White

Genotype Phenotype


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c. Heterozygous vs Heterozygous

• Ex Flower Color Dominant Blue
• Recessive White

Genotype Phenotype


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IV. Dihybrid Crosses

• Cross organisms with 2 different traits
• Possible Crosses
• Homozygous x Homozygous
• Heterozygous x Heterozygous

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a. Homozygous x Homozygous

• Ex Flower Color Dominant Purple
• Recessive White
• Flower Height Dominant Tall
• Recessive Short

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b. Heterozygous x Heterozygous

• Ex Flower Color Dominant Blue
• Recessive White
• Flower Height Dominant Tall
• Recessive Short

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V. Patterns of Inheritance

• 1. Complete Dominance Dominant trait completely
  masks recessive trait

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V. Patterns of Inheritance

• Incomplete Dominance
• Heterozygote has phenotype intermediate btwn
  phenotypes of two homozygotes
• -

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Incomplete Dominance
Flower Color Dominant Red (R) Recessive
White (r) Intermediate Pink


Genotype Phenotype
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VI. Codominance

• Codominance
• Phenotype of the heterozygote includes the
  phenotypes of both homozygotes
• No one allele is dominant, recessive, or blends
• Example animal fur color, blood types

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VII. Multiple Alleles

• Multiple Alleles
• More than two allele varieties are present within
  a group of individuals
• Varies genotype and phenotypes
• Example Blood Type ( ABO Group )

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Multiple Alleles
Blood Type Dominant Type A and
B Recessive Type O


Genotype Phenotype
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VIII. Sex Chromosomes

• Sex Determination
• Example
• Disorders/Syndromes
• Turner Syndrome 1 X 0 Y (female)
• Klinefelter Syndrome many X 1-2 Y (male)
• Poly-X females 3 X (female)

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IX. Sex-Linked Characteristics

• Determined by genes located on ________________
• Most are ____ -linked
• Example Color Blindness (X-linked)

Genotype Phenotype


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X. Pedigree Charts
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1. Autosomal Dominant
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2. Autosomal Recessive Heterozygotes carry the
recessive allele but exhibit the wildtype
phenotype