Mendel and Heredity Chapter 8

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Mendel and HeredityChapter 8

• Ms. Hogg, Biology

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The Origins of Genetics

• Heredity the passing of characteristics from
  parent to offspring
• Before DNA and chromosomes were discovered,
  heredity was one of the greatest mysteries of
  science!

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Gregor Mendel

• The scientific study of heredity began with
  Gregor Mendel
• Austrian monk
• Carried out experiments with garden peas
• He was the 1st to develop rules that accurately
  predict patterns of heredity.
• Father of Genetics

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Pea Plant
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7 Characteristics Mendel Studied
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Pollen Transfer in Mendels Experiments
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Mendels Hypotheses1

• For each inherited characteristic, an individual
  has two copies of the gene one from each parent.

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Mendels Hypotheses2

• There are alternative versions of genes.
• These different versions are called alleles.
• An individual receives one allele from each
  parent.

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Mendels Hypotheses3

• When two different alleles occur together, one of
  them may be completely expressed, while the other
  may have no observable affect on the organisms
  appearance.
• Dominant expressed trait
• Recessive trait that is NOT expressed

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Mendels Hypotheses4

• When gametes are formed, the alleles for each
  gene in an individual separate independently of
  one another.

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Terms of Genetics

• Homozygous two alleles of a gene are the SAME
• Example BB or bb
• Heterozygous two alleles of a gene are
  DIFFERENT
• Example Bb

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Terms of Genetics

• Genotype the set of alleles that an individual
  has for a trait
• Example BB
• Phenotype the physical appearance of a
  characteristic
• Example Brown hair

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Punnett Square

• A punnett square is a diagram that predicts the
  outcome of a genetic cross
• Monohybrid cross

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The Hardy-Weinberg Principle

• p2 2pq q2 1
• You can use this equation to predict genotype
  frequencies in a population.

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The Hardy-Weinberg Principle

• p2 2pq q2 1
• The sum of allele frequencies must always equal
  1.
• p q 1

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Exceptions

• The Hardy-Weinberg principle holds true for any
  population as long as evolutionary forces are not
  acting
• Mutations
• Gene flow
• Nonrandom mating
• Genetic drift
• Natural selection

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A ReviewMonohybrid Cross
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A ReviewDihybrid Cross
NOTE Must use the FOIL method to correctly set
up the parent genotype combinations on the
Punnett Square
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Incomplete Dominance

• An organism can display a phenotype that is
  intermediate between the two parents
• Example Snapdragon flowers
• RR red
• Rr pink
• rr white

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Incomplete Dominance
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Codominance

• Two dominant alleles can be expressed at the same
  time
• Example Human Blood groups
• (ABO blood groups)
• Type A IAIA or IAi
• Type B IBIB or IBi
• Type AB IAIB (Universal Recipient)
• Type O ii (Universal Donor)

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Codominance ABO Blood Groups
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Rh FactorSource NobelPrize.org
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Human Blood Type FrequencySource
RedCrossBlood.org
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Sex-linked Traits

• In sex-linked inheritance, the gene responsible
  for the disease is located on the
• X chromosome.
• Usually, the abnormal gene is recessive.
• For these reasons, the resultant disorder is
  called an X-linked recessive disease

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Sex-linked Disorders

• Color blindness
• A person with the most common form of color
  blindness cannot distinguish red from green hues.
  
• Hemophilia
• In hemophilia, the blood does not clot properly.

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Color blindness Tests
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Hemophilia
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Pedigrees
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Polygenic Traits

• Polygenic traits are controlled by two or more
  genes, usually on different chromosomes.
• Examples of Polygenic Traits
• Height, skin color, weight,
• Many common diseases, such as heart disease, are
  caused by polygenic genes and environmental
  factors (Lifestyle choices such as diet and
  exercise)

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Human skin color is controlled by at least eight
different loci on different chromosomes...