Genetics

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Genetics

• Genetics is the scientific study of heredity.
• Chapter 11
• Sections 1-3

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Gregor Mendel 1822
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11-1 The Work of Mendel

• 1822 Gregor Mendel used purebred pea plants to
  study the inheritance of traits.
• Fertilization the process in sexual
  reproduction in which male female reproductive
  cells join to form a new cell.

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Review of Meiosis How Gametes (Sex Cells) are
Formed
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Mendels Experiment with Pea Plants

• Mendel used the pea flower because they have both
  male female parts.
• Self-pollinating sperm cell in pollen fertilize
  the egg cells in the same flower. The offspring
  inherit characteristics from a single parent. Ex.
  Pea Plant flowers
• True-breeding- the pea plants flowers were
  self-pollinating and could produce offspring
  identical to themselves. i.e. they reproduced
  with themselves )

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Mendels Cross
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Describing Generations of a Punnett Square

• Original Parent plants P1 generation
• 1st set of offspring F1 generation
• 2nd set of offsprint F2 generation

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Experiment I Pea Plant

• Mendel wanted to prevent self-pollination so he
  made a controlled cross between 2 different
  plants.
• He cut away the male parts dusted pollen from
  another plant on the flower.
• Cross-pollination seeds produced are the
  offspring of 2 different parents.
• Accomplished by breeding 2 different plants
  together.
• Mendel studied specific characteristics of the
  pea plant such as color height.

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Mendel Studies 7 Traits / Characters pg. 264

• Seed Shape
• Seed Color
• Seed Coat Color
• Pod Shape
• Pod Color
• Flower Position
• Plant Height

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The Traits Mendel Crossed
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Genes and Dominance

• Mendel crossed 2 different plants that carried
  different forms for the same trait.
• Ex. 1 tall plant crossed with 1 short plant
• The plants that grew were hybrid.
• Hybrid are the offspring of crosses between
  parents with different traits.

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Experiment I Concluded

• Traits are inherited through the passing of
  factors from parents to offspring.
• The hybrid plants looked like only 1 parent and
  the trait of the other parent plant seemed to
  disappear.
• Each trait is controlled by 1 gene.
• Genes chemical factors that determine traits.
• Alleles different forms of a gene.
• EX Tall plants or Short plants

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Alleles Different forms of a gene
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Principle of Dominance

• States that some alleles are dominant others
  are recessive.
• Whenever a living thing inherits a dominant
  allele, that trait is visible.
• The effects of a recessive allele are not seen if
  the dominant allele is present.

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Experiment II Segregation

• Mendel crossed a tall plant (dominant) with a
  short plant (recessive),
• the F1 plant inherited an allele for tallness
  from the tall parent an allele for shortness
  from the short parent. Pg. 265

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The Law of Segregation in the F1 Generation
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Now the F2 Generation
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What happened to the recessive allele?

• Mendel allowed his hybrid plants to
  self-pollinate.
• Some showed recessive traits, the recessive
  traits did not disappear.
• Earlier, the dominant masked the recessive, so it
  was not visible.

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Experiment II Conclusion

• Alleles for the same trait can be separated.
• Segregation When sex cells, or gametes, are
  formed. Each gamete carries only 1 copy of each
  gene.
• Therefore, each F1 plant produces 2 types of
  gametes (some with an allele for purple flowers
  some with an allele for white flowers). Ex.
  Gametes with P, p, P, p offspring with PP, Pp,
  Pp, pp

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11-2 Probability Punnett Squares

• Probability the likelihood that a particular
  event will occur.
• Ex. Flipping a coin. The probability that it
  will land on tails is ½.

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The Principles of Probability

• It is used to predict the traits of the offspring
  produced by genetic crosses.
• Mendel used a Punnett Square to show the gene
  combinations that might result from a genetic
  cross.

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Punnett Squares

• The F1 parent is shown along the top left
  sides.
• The possible F2 offspring are in the 4 boxes that
  make up the square.
• Letters represent alleles.
• T is dominant allele for tallness.
• t is recessive allele for shortness.
• Pg. 268

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The Punnett Square show

• All the possible results of a genetic cross.
• The genotypes of the offspring.
• The alleles in the gametes of each parent.

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Punnett Squares

• Homozygous organisms that have 2 identical
  alleles for a particular trait they are
  true-breeding. Ex. TT or tt
• Heterozygous organisms that have 2 different
  alleles for the same trait they are hybrid. Ex
  Tt
• Genotype genetic make up.
• Phenotype Physical characteristics dont have
  the same genotype.

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Homozygous Vs. Heterozygous Genotype Vs.
Phenotype
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Probability of SegregationPg. 268-269

• ¼ (25) of F2 plants have 2 alleles for tallness
  (TT).
• ½ (50) of F2 plants have 1 allele for tallness
  1 allele for shortness (Tt).
• ¾ (75) of F2 plants are tall because the allele
  for tallness is dominant over allele for
  shortness.
• Overall, there are 3 tall for every 1 short plant
  in F2 generation Ratio of 31

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11-3 Independent Assortment 2 Factor Crosses

• states that during gamete (sex cell) formation,
  genes for different traits separate independently
  with out influencing each others inheritance.
• Helps account for genetic variations.
• Ex. Pea shape pea color are separate traits
  controlled by separate genes.

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Experiment III The Two-Factor Cross F1

• Mendel crossed true-breeding plants - round
  yellow peas (RRYY) with wrinkled green peas
  (rryy)
• The F1 offspring were all round yellow showing
  that both were dominant alleles. The genotype is
  RrYy. Pg. 270

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Experiment IIIThe Two-Factor Cross F2

• The F1 plants were all heterozygous with a
  genotype of RrYy.
• The F1 plants were segregated to each other to
  produce an F2 generation.
• Mendel compared the variations in the seeds.

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2- Factor (Trait) Crosses
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Experiment III Conclusion

• Mendel found some offspring that were
• Round / yellow (P phenotype)
• Wrinkled / green (P phenotype)
• Many with combinations of alleles (not found in
  either parent)
• This showed that the alleles for seed shape
  segregated independently of those for seed color
  (independent assortment). Pg. 271

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Summary of Mendels Principles

• Genes are passed from parents to their offspring.
• Some forms of the gene may be dominant and others
  may be recessive.
• Each adult has 2 copies of each gene one from
  each parent. The genes are segregated from each
  other when gametes are formed.
• Alleles for different genes usually segregate
  independently of one another.

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Different Patterns of Dominant Recessive

• Incomplete Dominance 1 allele is not completely
  dominant over another. Ex. Red flower (RR)
  white flower (WW), F1 is a pink flower (RW). Pg.
  272
• Codominance both alleles contribute to the
  phenotype.
• Ex. A cross of a black chicken (BB) with a
  white chicken (WW) will produce all speckled
  offspring (BBWW) colors appear separately.

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Incomplete Dominance a blend of 2 taits
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CoDominance Both Forms of the Trait are Expressed
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Different Patterns of Dominant Recessive

• Multiple Alleles have more than 2 alleles. Ex.
  Coat color in rabbits.
• Polygenic Traits traits controlled by 2 or more
  genes having many genes. Ex. Variation in
  human skin color.

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Human Blood Type has Multiple Alleles
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Skin Color Polygeneic Trait (More than one gene
controls the pheonotype
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Thomas Hunt Morgan

• Geneticist who looked for a model organism to use
  in studying genetics
• He chose the fruit fly because it produces large
  numbers of offspring.

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Genes the Environment

• Mendels principles apply to all organisms not
  just plants.
• Characteristics of any organism are not
  determined solely by genes it inherits.
• Characteristics are determined by interaction
  between genes and the environment.
• Ex. Genes affect the height and color of a
  sunflower but the same characteristics are
  influenced by climate, soil, conditions, and
  availability of water.
• Genes provide a plan for development, but how the
  plan unfolds depends on the environment.