Mendel and the Gene Idea

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Mendel and the Gene Idea

• Chapter 11.1-3

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Who was Gregor Mendel?

• The Father of Genetics
• Austrian monk with a scientific background -
  studied under Doppler at University of Vienna
• studied the heredity of pea plants
• first person to succeed in predicting how traits
  are passed from one generation to the next.

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Mendels Experiment

• how did one character with 2 different traits get
  passed on?
• Needed two true-breeding parents (P generation)
• Cross-pollinated the two different strains
• This is called a monohybrid cross.

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Mendels Experiment (contd)

• The first filial generation (F1) produced from
  the true-breeding P parents showed only the trait
  from one parent.
• Mendel allowed the F1s to self-pollinate and the
  result was surprising! Both traits from the P
  generation resurfaced in the F2 generation, in a
  31 ratio

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Mendels Results

• From the monohybrid cross, Mendel established
• rule of unit factors each organism must have 2
  factors that control its traits genes and
  alleles
• rule of dominance one factor (dominant) may mask
  the presence of another (recessive)
• LAW OF SEGREGATION

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LAW OF SEGREGATION

• explains the results of a monohybrid cross
• The two alleles for each trait must separate when
  gametes are formed.
• Parents pass on, at random, only one allele for
  each trait to each offspring.
• During fertilization, gametes randomly pair to
  produce 4 possible combinations

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Mendels Dihybrid Cross Experiment

• Mendel studied how traits affect each other
  during a dihybrid cross studying 2 traits at
  once.
• Tried to discover whether or not traits are
  inherited independently.
• Dependent assortment parental pairs of traits
  are passed together
• Independent assortment each factor is passed on
  independently.

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LAW OF INDEPENDENT ASSORTMENT

• explains the results of a dihybrid cross
• genes for different traits are inherited
  independently of each other
• when two dihybrid individuals mate they produce
  four different offspring in a 9331 ratio
• if the alleles were inherited together, then only
  two offspring would be possible

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Mendels Impact - Summary

• Also known as the _____ of ____
• Rule of _____ _____ states that ______ are
  passed from parent to offspring.
• Rule of ________ _______ alleles mask the
  presence of ______ alleles.
• Law of ________ states ?
• Law of ________ ___________ states?

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Beyond Mendels Ideas

• Pea each trait has only 1 gene each gene had
  only 2 alleles.
• Natural world (esp. humans) NOT SO SIMPLE!!!
• There are 4 major exceptions to Mendels Rules

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Exceptions to Rule of Dominance

• Incomplete dominance one allele is not
  completely dominant over another. Results in an
  intermediate (blend) phenotype in a heterozygous
  individual
• Codominance both alleles are expressed equally
  in the phenotype. Results in a phenotype with
  both traits present in a heterozygote

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Exceptions to Rule ofUnit Factors

• Multiple alleles more than 2 alleles control the
  expression of 1 gene. Results in extra phenotypes
  and genotypes.
• Polygenic traits more than 1 gene controls a
  given trait. Results in a bell-shaped (normal)
  curve of phenotypes.

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Chapter 12 Patterns of Heredity and Human
Genetics
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Objectives 12.1

• Interpret a pedigree
• Determine human genetic disorders that are caused
  by inheritance of recessive alleles
• Predict how a human trait can be determined by a
  simple dominant allele

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Objectives 12.2

• Distinguish between incompletely dominant and
  codominant alleles
• Compare multiple allelic and polygenic
  inheritance
• Analyze the pattern of sex-linked inheritance
• Summarize how internal and external environments
  affect gene expression

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Objectives 12.3

• Compare codominance, multiple allelic,
  sex-linked, and polygenic patterns of inheritance
  in humans
• Distinguish among conditions in which extra
  autosomal or sex chromosomes exist

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Chapter 13 Genetic Technology
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Objectives 13.1

• Predict the outcome of a test cross
• Evaluate the importance of plant and animal
  breeding to humans

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Objectives 13.2

• Summarize the steps used to engineer transgenic
  organisms
• Give examples of applications and benefits of
  genetic engineering