Mendelian Inheritance

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Mendelian Inheritance
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Gregor Mendel

• Father of genetics
• First person to successfully predict how traits
  are transferred from one generation to the next

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Garden Pea Plants

• Reproduce sexually
• Have distinct male and female sex cells (gametes)
  in the same flower

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Monohybrid cross

• Cross for only one trait
• Legend
• P1 Parents
• F1 First filial (son or daughter) generation
• F2 Second filial generation

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Mendels Monohybrid Crosses
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The rule of unit factors

• Mendel concluded
• Each organism has two factors for each trait
  called genes
• Two alleles for shortness, two alleles for
  tallness
• Alleles are alternative forms for genes
• Alleles are found on different copies of a
  chromosome (one from mom, one from dad)

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The rule of dominance

• Dominant trait
• Trait that is observed
• Recessive trait
• Trait that disappears

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Law of Segregation

• Two alleles for each trait must separate when
  gametes are formed
• A parent passes on at random only one allele for
  each trait to each offspring

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Phenotypes and Genotypes

• Genotype
• Gene combination of an organism
• Tt, RR
• Phenotype
• The way an organism looks
• Tt tall plant
• RR round pea

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• Homozygous
• Two alleles for the trait are the same
• RR, rr
• Heterozygous
• Two alleles for the trait are different
• Rr

Homozygous alleles
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Dihybrid Crosses

• A cross involving two different traits
• Crossed plants with round yellow seeds and
  wrinkled green seeds
• RRYY x rryy

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Parent
Round, yellow
Wrinkled, green
Cross fertilization
Self fertilization
All round, yellow
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Law of Independent Assortment

• Genes for different traits are inherited
  independently of each other

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Punnett Squares

• Discovered by Reginald Punnett, 1905
• Predicts expected proportions of possible
  genotypes in the offspring of the cross

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Monohybrid cross
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Dihybrid cross