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Dominant and Recessive Traits (PowerPoint)

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					Dominant and Recessive
        Traits
             Remember . . .
• You receive one allele from each parent,
  per trait

• The alleles can be different, but they are
  for the same trait (i.e. hair color, eye color,
  etc.)
                  Mendel
• Modern genetics had its beginnings in an
  abbey garden, where a monk named Gregor
  Mendel documented a particulate mechanism
  of inheritance.

• He discovered the basic principles of heredity
  by breeding garden peas in carefully planned
  experiments.
             Mendel’s work
• In order to study inheritance, Mendel chose
  to use peas, probably as they are available
  in many varieties.

• The use of plants also allowed strict control
  over the mating.

• He chose to study 7 observable traits
               Seven Observable Traits
Charateristic                 Possible Traits

Plant Height                  Long or Short Stems

Flower Position around Stem   Axial or Terminal



Pod Color                     Green or Yellow

Pod Appearance                Inflated or Constricted

Seed Texture                  Smooth or Wrinkled

Seed Color                    Yellow or Green

Flower Color                  Purple or White
             Genetic crosses
• He transferred pollen from
  a true breeding white flower
  to the carpel of a true
  breeding purple flower.
            Tracking heritable
             characteristics
• Mendel tracked heritable
  characters for 3
  generations.

• In the 3rd generation,
  Mendel noticed that the
  white flower reappeared
          Mendel’s terminology
• True breeding: When the plants self-pollinate, all
          their offspring are of the same variety.

• P generation: Parent generation. Each parent is
  pure-bred, but different

• F1 generation: First generation. The “kids” of the
  parent generation

• F2 generation: Second generation. The
  “grandkids” of the parent generation. This is where
  the white flower reappears.
         Mendel’s     Law: 1 st

      Principle of Segregation
• Alleles result in variation in inherited traits

• For each gene there are 2 alleles
  – One from each parent

• The Dominant allele will always be
  expressed
          Dominant Traits
• Always displayed in the phenotype

• Represented by CAPITAL LETTERS



Brown Hair: B
          Dominant Traits
• A person will show a dominant phenotype
  if their genotype is one of the following
  combinations:

Brown Hair = B           Blond Hair = b


                 BB      Bb
         Recessive Traits
• Only show up when 2 of the same
  recessive traits are paired up

• Represented by lowercase letters



Blond Hair: b
           Example #1
Both your father and your mother give you
an allele for brown eyes (B).

What is your genotype?

What is your phenotype?
           Example #2
Both your father and your mother give you
an allele for blue eyes (b).

What is your genotype?

What is your phenotype?
            Example #3
The presence of freckles is a dominant
trait (F). If you father gave you the allele
for freckles (F) and your mother gave you
the allele for no freckles (f), what is your
genotype and phenotype?
            Example #4
The presence of a chin dimple is a
recessive trait. Your father gives you (c)
and your mother gives you (C).

What is your genotype?

What is your phenotype?
           Example #5
The presence of a widows peak is a
dominant trait (W). Your father gives you
(w) and your mother gives you (w).

What is your genotype?

What is your phenotype?
            Principle of
      Independent Assortment
• Allele pairs separate independently during
  the formation of gametes

• Traits are transmitted to offspring
  independently of one another


i.e. Hair color does not depend upon eye
     color
    Independent Assortment
• Occurs because traits are located at
  different spots or on completely different
  chromosomes

				
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