Chapter 14 Mendel and the Gene Idea

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Chapter 14 Mendel and the Gene Idea
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Inheritance
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Genetics
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Genetic Theories

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Genetic Theories (cont.)
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Gregor Mendel
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• Mendels paper published in 1866, but was not
  recognized by Science until the early 1900s.

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Reasons for Mendel's Success
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• Mendel was a pea picker.
• He used peas as his study organism.

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Why Use Peas?
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Cross-pollination
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Self-pollination
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Mendel's Work
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Monohybrid or Mendelian Crosses
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P Generation
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Offspring
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Another Sample Cross

• P1 Tall X short (TT x tt)
• F1 all Tall (Tt)
• F2 3 tall to 1 short
• (1 TT 2 Tt 1 tt)

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Results - Summary
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Mendel's Hypothesis
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Mendel's Hypothesis
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Mendel's Hypothesis

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Law of Segregation
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Mendels Experiments
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Vocabulary
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Helpful Vocabulary
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6 Mendelian Crosses are Possible

• Cross Genotype Phenotype
• TT X tt all Tt all Dom
• Tt X Tt 1TT2Tt1tt 3 Dom 1 Res
• TT X TT all TT all Dom
• tt X tt all tt all Res
• TT X Tt 1TT1Tt all Dom
• Tt X tt 1Tt1tt 1 Dom 1 Res

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Test Cross
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Dihybrid Cross
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Number of Kinds of Gametes
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Equation

• The formula 2n can be used, where n the
  number of heterozygous traits.
• Ex TtRr, n2
• 22 or 4 different kinds of gametes are
  possible.
• TR, tR, Tr, tr

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Dihybrid Cross
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Results

• 9 Tall, Red flowered
• 3 Tall, white flowered
• 3 short, Red flowered
• 1 short, white flowered
• Or 9331

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Law of Independent Assortment
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Comment
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Probability
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Genetic Ratios
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Rule of Multiplication
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Example TtRr X TtRr
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Comment
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Variations on Mendel
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Incomplete Dominance
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Result
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Another example
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Codominance
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Result
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Multiple Alleles
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Result
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Alleles and Blood Types

• Type Genotypes
• A IA IA or IAi
• B IB IB or IBi
• AB IAIB
• O ii

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Comment
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Epistasis
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Gerbils
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In Gerbils

• CcBb X CcBb
• Brown X Brown
• F1 9 brown (C_B_)
• 3 black (C_bb)
• 4 albino (cc__)

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Result
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Epistasis in Mice
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Problem

• Wife is type A
• Husband is type AB
• Child is type O
• Question - Is this possible?
• Comment - Wifes boss is type O

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Bombay Effect
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Genotypes
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Bombay - Detection
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Polygenic Inheritance
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Genetic Basis
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Result
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Genetic Studies in Humans
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Pedigree Chart Symbols

• Male
• Female
• Person with trait

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Sample Pedigree
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Recessive Trait
Dominant Trait
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Human Recessive Disorders
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Sickle-cell Disease
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Tay-Sachs
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Cystic Fibrosis
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Recessive Pattern
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Human Dominant Disorders
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Inheritance Pattern
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Genetic Screening
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General Formal

• R F X M X D
• R risk
• F probability that the female carries the gene.
• M probability that the male carries the gene.
• D Disease risk under best conditions.

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Example
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Risk Calculation

• Wife probability is 1.0 that she has the
  allele.
• Husband with no family record, probability is
  near 0.
• Disease this is a recessive trait, so risk is
  Aa X Aa .25
• R 1 X 0 X .25
• R 0

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Risk Calculation

• Assume husband is a carrier, then the risk is
• R 1 X 1 X .25
• R .25
• There is a .25 chance that any child will be
  albino.

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Common Mistake
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Carrier Recognition
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Fetal Testing
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Amniocentesis
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Chorionic Villi Sampling
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Newborn Screening
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Newborn Screening
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Multifactorial Diseases
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Ex. Heart Disease
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Summary

• Know the Mendelian crosses and their patterns.
• Be able to work simple genetic problems
  (practice).
• Watch genetic vocabulary.
• Be able to read pedigree charts.

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Summary

• Be able to recognize and work with some of the
  common human trait examples.