Monohybrid Crosses

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Monohybrid Crosses

• Joohee Kim
• IB Biology
• Sec. III

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Definition

• Tracking inheritance pattern of a single trait
  between 2 individual organisms

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Mendel

• Discovered basic rules of inheritance
• Analyzed offspring of pea mating

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Punnett Square

• Tt x Tt genotype
• Tt x Tt gametes

Male gametes
T t
TT Tt
tT tt
T t
Female gametes

• Mandelian ratios Genotypic- 1TT2Tt1tt
• Phenotypic- 3 dominant 1 recessive

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Patterns of Inheritance

• DNA is passed on to the next generation
• In sexual species, the DNA will be a mix of both
  parents.
• There are ways to predict how this new DNA will
  behave and be expressed
• - Genotype and Phenotype

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Transmission Genetics

• Gregor Mendel in the 1860s
• Botanical Crosses
• Monohybrid Crosses
• Mendels Principles of Inheritance

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Solving a Genetics Problem

• Trait - dominant A (AA or Aa)
• Trait recessive a (aa)
• _____ x _____
• Punnett Square
• Answer questions based on results from Punnet
  Square

___ ___


___ ___
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Monohybrid Crosses

• Cross that involves one pair of contrasting
  traits
• Solve using Punnett Square
• Sample problems
• - Rr x rr
• - RR x rr
• - Rr x Rr
• - Rr x RR

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Problem

• Short hair (L) is dominant to long hair (l) in
  mice. What is the genotype and phenotype ratio of
  a heterozygous short-haired mouse crossed with a
  long-haired mouse?

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Solution

• Short hair dominant L (LL or Ll)
• Long hair recessive l
• Ll x II (heterozygote parent Ll)
• Punnett Square
• Genotype ratio ½ Ll ½ ll
• Phenotype ratio ½ short hair ½ long hair

L l
l Ll ll
l Ll ll
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Link for Video

• http//www.zerobio.com/videos/monohybrid.html