Mendel's Laws on Heredity

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Chapter 10.1

• Mendel's Laws on Heredity

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Objectives(Do not write)

• Analyze the results obtained by Gregor Mendel.
• Predict the possible offspring of a genetic cross
  by using a punnett square.

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Heredity

• Organisms inherit, or receive, their
  characteristics from their parents.
• A characteristic, or feature, of an organism is
  also called a trait.

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• The passing of traits from parents to young is
  called heredity.
• The study of heredity is called genetics

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Gregor Mendel

• Monk who lived in the 1800s
• Studied the heredity of pea plants that he grew
• Mendels findings about heredity of pea plants
  have been shown to apply to other organisms.

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• Some of mendels methods are still used in the
  modern study of heredity.

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• The mating of organisms to test traits is called
  a cross. The results of a cross are the offspring.

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• Mendel began his work by using purebred pea
  plants.
• An organism is purebred for a trait if when
  self-pollinated the same form of a trait is shown
  in all of its offspring.

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• In a purebred, the same trait appears in many
  generations when the organisms are self pollinated

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• In his first experiment, Mendel crossed purebred
  tall with a purebred short pea plant, which
  produced 4 tall offspring.
• The tall plants produced in this cross are called
  hybrids.
• A hybrid is an organism that is produced by a
  cross of parents that have different forms of a
  trait

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• A dominant trait prevents another trait from
  showing
• A recessive trait is hidden by the presence of a
  dominant trait.

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Inheritance of traits

• In his work with pea plants, Mendel studied pairs
  of contrasting traits

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• In each case, two purebred plants with
  contrasting traits were crossed.
• Then the hybrid offspring were self-pollinated to
  produce a second offspring generation.

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• In this generation, there were three times as
  many plants with one trait as there were plants
  with the contrasting trait.

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He reported these conclusions about traits

1. Organisms inherit traits in pairs. An organism
   receives one trait from each of its two parents.
2. Some traits are dominant others are recessive.
   In hybrids dominant traits hide recessive traits.
   Recessive traits show only when no dominant trait
   is present

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• Mendel used a system of symbols to show what
  traits an organism had and to show what traits
  were passed on to offspring.
• T Dominant
• t recessive

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• The inherited appearance of an organism is its
  phenotype
• The genetic make-up of an organism is its
  genotype
• Forms of a gene (traits) are called alleles.

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• A punnett square is a chart that shows all the
  possible combinations of traits among offspring
  of a cross

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Probability and Punnett squares

• Probability is the likelihood that a particular
  event will occur.
• Flip a coin there are two probable outcomes
• Flip a coin three times
• Each time is an independent event

• The probability of flipping three heads
• ½ x ½ x ½ 1/8
• The principles of probability can be used to
  predict the outcomes of genetic crosses

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Incomplete Dominance

• You have learned that in pairs of traits one is
  dominant and one is recessive.
• Not all pairs of traits are like this.
• Incomplete dominance is a condition in which
  neither trait of a pair is dominant or recessive

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Terms

• Homozygous-
• organisms that have two identical alleles for a
  particular trait TT, tt.
• These are true-breeding for a particular trait

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• Heterozygous
• organisms that have two different alleles for the
  same trait. Tt
• These are hybrid for a particular trait.