Chapter 11 Observable Patterns of Inheritance

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Chapter 11 Observable Patterns of Inheritance Powered By Docstoc
					     Chapter 11
Observable Patterns of
• Father of inheritance: Gregor Mendel
  Mendel’s Insight Into Inheritance
• Natural selection suggested that a
  population could evolve if members
  showed variation in heritable traits
• Variations that improved survival chances
  would be more common in each
  generation –in time, population would
  change over time or evolve
 Mendel’s Experimental Approach
• Gregor Mendel used experiments in plant
  breeding and a knowledge of mathematics
  to form his hypothesis
  – He used green pea plants in his experiment
    • This plant can self-fertlize itself
    • True-breeding (white flowerwhite flower)
    • Cross-fertilized by human manipulation of the
  – Mendel crossed-fertilized true-breeding
    garden pea plants having clearly constrasting
Genetic terms (found on p. 179)
• Genes: units of information about specific
• Locus: Each gene has a location of
• Homologous chromosome: diploid cells
  have two genes (a gene pair) for each trait
• Alleles are various molecular forms of
  gene for the same trait
• True-breeding lineage occurs when
  offspring inherited identical alleles,
  generation after generation
• Hybrid Non-identical alleles
• Homozygous alleles: both alleles are the
  – RR: Homozygous Dominant
  – rr: Homozygous Recessive
• Heterozygous: One allele is dominant and
  other is recessive
  – Rr: Heterozygous Dominant
• Dominant: more organisms in the
  population with particular trait (represent
  with a capital letter)
• Recessive: very few organisms in the
  population with the trait (represent with a
  lowercase letter)
• Genotype: the genetic makeup of an
  – How many are homozygous dominant,
    heterozygous dominant, and homozygous
• Phenotype: Physical appearance
  – Adjectives (describe the appearance)
  – How many are dominant and recessive?
• P- Parent Generation
• F1 First generation
• F2 Second generation
         Law of Segregation
• States that 2n (diploid) organisms inherit
  two genes per trait located on pairs of
  homologous chromosomes
• During meiosis the genes segregate from
  each other such that each gamete will
  receive only one gene per trait.
        Monohybrid Crosses
• Monohybrid crosses have two parents that
  are true-breeding for contrasting forms of
  a trait
• Self-fertilization: one form of the trait
  disappears in the first generation offspring
  (F1), only to show up in the second
• We know now that all members in the
  second generation are heterozygous
            F2 Generation
• A genetic cross of a F2 generation would
  show up a 3:1 phenotypic ratio
  Steps to a Monohybrid Cross
• Look up on the board to see the steps to a
  monohybrid cross
• To support his concept of segregation,
  Mendel crossed F1 plants with
  homozygous recessive individuals
• A 1:1 ratio of recessive and dominant
  phenotypes supported his hypothesis
Law of Independent Assortment
• States that during meiosis each gene of a
  pair tends to assort into gametes
  independently of other gene pairs located
  on nonhomologous chromosomes
• Mendel showed F1 were all dominant for
  purple flowers and tall
          Dihybrid Crosses
• Steps on the board
      Incomplete Dominance
• A dominant allele cannot completely mask
  the expression of another
• Snapdragons
• ABO blood types
• Both alleles are expressed in
  – Humans with both proteins are designated
    with blood type AB
       Multiple Allele System
• Whenever more than two forms of alleles
  exist at a given locus
  – Example: Four blood types: A, B, AB and O
  Multiple Effects of Single Genes
• Pleiotropy: The expression of alleles at one
  location can have effects on two or more
• Example: Marfan Syndrome
• (Abe Lincoln)
  – Gene for codes for a variant form of fibrillin1,
    a protein in the extracellular matrix of
    connective tissues
     • Causes weakening connective tissues throughout
       the body
     • Effects: lanky skeleton, leaky heart valves, and
       weakened blood vessels, lens displacement
   Interactions Between Gene
• Epistasis: One gene pair can influence
  other gene pairs, with their combined
  activities producing some effect on

• Example: Coat Color in Mice
  – Chicken Combs (Red portion on their heads)
      Hair Color in Mammals
• In Labrador retrievers, one gene pair
  codes for the quantity of melanin produced
  while another codes for melanin deposition
• Another gene locus determines whether
  melanin will be produced at all
       Comb Shape in Poultry
• Sometimes interactions between two pairs
  results in a phenotype that neither pair
  can produce alone
• Comb shape in chickens is of at least four
  types depending on the interactions of two
  gene pairs

Rose      Pea         Single   Walnut
    Regarding the Unexpected
• Tracking even a single gene through
  several generation may produce results that
  are different
• Camptodactyly (Immobile, bent fingers) can
  express itself on both or one hand because
  a possible
gene product is missing
           Polygenic Traits
• Traits expressed by more than one gene
• Eye Color (Three genes play a role of eye
       Environmental Effects
• Fur on extremities of certain
animals will be darker because
 the enzyme for melanin production
 will operate at cooler temperature but is
   sensitive to
heat on the rest of the body.
• Hydrangea Plants: the color of floral
cluster based on the acidity of the soil

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