GT Chapter 13 Honors Ch 11

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GT Chapter 13Honors Ch 11 14

• Patterns of Inheritance

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Patterns of Inheritance

• Look around you.
• Variation can be seen everywhere you look.
• Your classmates have different color eyes, hair,
  and skin. They are different heights and have
  different bone structures.
• We are going to explore the differences and how
  the environment and genetics cause these.

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Heredity and the Environment

• While you may have inherited your height and body
  build from your parents, the environment also
  affects these traits.
• Nutrition and exercise are two environmental
  factors that can affect height and body build.

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Mendel

• Mendel is considered to be the father of
  genetics.
• He conducted carefully controlled experiments
  with pea plants and discovered the basic
  principles of heredity.
• Mendel was a friar at the Augustinian monastery
  in Brno, Czechoslovakia.

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• Mendel was experimenting with flowers in the
  monastery's gardens, trying to develop new color
  variations.
• It was these experiments that led to his
  experiments in hybridization.
• But Mendel was not alone in his field... ever
  since humans began domesticating plants and
  animals (at least 10,000 years ago), we wondered
  how traits were passed from parent to offspring.
• One belief was that traits were stored as
  'particles' in the parts of each parent's body
  and 'blended' in the offspring. This theory left
  many questions untackled, however.

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• In the 18th and 19th centuries, scientists tried
  to unravel these questions, but their means
  returned inconclusive results.
• Unlike the others, Mendel studied only one trait
  at a time.
• Because of this, he was the first to be able to
  describe the relations between parents and
  children with mathematical symbols.

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Useful Vocabulary

• Genetics the study of inheritance.
• Character- heritable trait such as flower color
  or hair color.
• Trait the variant for the character purple
  flowers, red hair.

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Mendels Experiments

• Mendel chose a common garden pea (Pisum) for his
  first experiments in hybridization.
• These plants exhibited what are now called
  "Mendelian Traits" - traits which occur in a very
  simple form. (These are traits that only have two
  forms- green peas or yellow peas red flowers or
  white flowers).

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• When Mendel started his experiments, he
  immediately noticed that when breeding two peas,
  a particular variation of a trait in one pea (for
  example, the greenness of a pea) would not appear
  in the next generation.
• However, in the following generation, when
  breeding the offspring together, this variation
  would appear again.
• He concluded that the traits were being "masked"
  in the second generation, to be exhibited again
  in the third.

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• When two plants breed, the variations of their
  traits are combined. The combination can only be
  explained by assuming that, for each trait, there
  is space for two pieces of "information"
  describing the variation.
• Say we have a pea which is "purebred" to green
  (that is, when it is bred with itself, it will
  create only green peas), and another which is
  "purebred" to yellow. If we breed a purebred
  green pea and a purebred yellow pea, and our
  result is all yellow peas, we can say that the
  "green" variation has been lost. However, since
  in the next generation, yellow peas appear again,
  we must instead say that the "green" variation
  was masked, not lost.

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Vocabulary

• Traits that masked other traits, are described
  as dominant.
• Traits that are masked are said to be
  recessive.
• The standard way of labeling the variation
  information of a trait in a particular organism
  is using two letters.
• Capital letters represent information which is
  dominant.
• Lowercase letters represent the recessive. The
  letter being used describes a variation (usually
  the recessive) of the trait.

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Generations

• P generation is the parent generation.
• F1 is the first filial generation or the
  offspring of the P generation.
• F2 is the second filial generation or the
  offspring of the F1 generation.

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Generations
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Mendels Law of Segregation

• The Law of Segregation states that the members of
  each pair of alleles separate when gametes are
  formed. A gamete will receive one allele or the
  other.
• In other words, two alleles for a character are
  packaged into separate gametes (one from the
  maternal line and one from the paternal line.)

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Mendels Law of Independent Assortment

• The Law of Independent assortment states that two
  or more pairs of alleles segregate independently
  of one another during gamete formation.
• Or- alleles for a characteristic divide up among
  gametes (during meiosis) independently of one
  another.

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Alleles

• Alleles can be dominant or recessive.
• Individuals can be homozygous dominant (BB),
  homozygous recessive (bb) or heterozygous (Bb).
• In homozygous dominant and heterozygous
  individuals the dominant trait is expressed.
• For a recessive trait to be expressed, the
  individual must be homozygous recessive.

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Phenotype and Genotype

• The phenotype is the exhibited or expressed
  traits.
• The genotype is the genetic make-up.
• The genotype and phenotype are the same for
  homozygous individuals.
• Heterozygotes are more difficult to determine
  because they carry the recessive trait even
  though it is not expressed.

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Probability and Punnett Squares

• We can determine the probability of traits shown
  in potential offspring of two individuals by
  using a Punnett Square.
• The probabilities are just like tossing a coin.

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Probability

• Probability ranges from 1 very certain an event
  will happen to 0 the event will not happen.
• What is the probability that a coin when tossed
  will land on heads?
• What is the probability that when tossed two
  coins will both land on heads.

½ x ½ ¼
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Using Probability to Solve Genetic Problems

• We can use the Punnet square to calculate the
  number of offspring likely to result from the
  individuals of known genotype.
• Draw a 4-square Punnet square and determine the
  likely numbers of offspring for the following
  crosses.
• TT x tt and Bb x bb

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• T tall, t short
• B brown eyes, b blue

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Dihybrid Cross

• T tall, t short
• B brown eyes, b blue
• TtBB x ttBb
• FOIL is used to determine the genotypes.
• Using the above parents, calculate the probable
  numbers of offspring with the traits that result
  from this cross.

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TtBB x ttBb
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Tri-Hybrid Cross

• If R tongue roller, r non-roller then
  calculate TTbbRr x Ttbbrr

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Other forms of Inheritance

• Genetics is not simple.
• There are more complex gene interactions that
  occur other than what we term simple Mendelian
  genetics

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Incomplete Dominance

• Incomplete dominance when neither allele is
  dominant over the other and a blending of the
  traits is the result. Example Hair Texture.
• Curly and Straight hair textures show incomplete
  dominance. CC curly, SS straight and CS
  wavy.

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Codominance

• Another example is codominance.
• Codominance is when both alleles are dominant and
  both traits show in the genotype.
• Blood Groups are an example.
• I is used for blood.

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Blood Groups

• IA is for type A.
• IB is for type B
• i is for type 0
• Persons with type A can be IA i or IA IA
• Persons with type B can be IB i or IB IB
• Persons with Type AB are IA IB
• Persons with 0 are ii.

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Genetic Expression and the Environment

• Phenotypes are always affected by their
  environment. In buttercup (Ranunculus peltatus),
  leaves below water-level are finely divided and
  those above water-level are broad, floating,
  photosynthetic leaf-like leaves.
• Siamese cats are darker on their extremities, due
  to temperature effects on phenotypic expression.
  Expression of phenotype is a result of
  interaction between genes and environment.

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• Siamese cats and Himalayan rabbits both animals
  have dark colored fur on their extremities.
• This is caused by an allele that controls pigment
  production being able only to function at the
  lower temperatures of those extremities.
• Environment determines the phenotypic pattern of
  expression.

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Polygenic Inheritance

• Polygenic inheritance is a pattern responsible
  for many features that seem simple on the
  surface. Many traits such as height, shape,
  weight, color, and metabolic rate are governed by
  the cumulative effects of many genes.
• Polygenic traits are not expressed as absolute
  characters, as was the case with the pea plant
  traits.

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• Instead, polygenic traits are recognizable by
  their expression as a gradation of small
  differences (a continuous variation). The results
  form a bell shaped curve, with a mean value and
  extremes in either direction.
• Usually polygenic traits are distinguished by
• Traits are usually quantified by measurement
  rather than counting.
• Two or more gene pairs contribute to the
  phenotype.
• Phenotypic expression of polygenic traits varies
  over a wide range.

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Linked Genes

• Genes close together on same chromosome are
  called linked genes
• Linked genes do not exhibit independent
  assortment and they move together during crossing
  over if they are very close together on the
  chromosome.

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Sex Linked Genes

• Genes that are located on the x chromosome are
  sex linked.
• It is called an x-linked trait and is only
  carried on the x chromosome.
• Red-green colorblindness, hemophilia, and male
  pattern baldness are examples of x-linked traits.

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Sex-Linked Genes