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Patterns of Heredity (Chapter 4 pp. 98-127)


Patterns of Heredity (Chapter 4 pp. 98-127) T. Gilbert 7th Life Science – PowerPoint PPT presentation

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Title: Patterns of Heredity (Chapter 4 pp. 98-127)

Patterns of Heredity (Chapter 4 pp. 98-127)
  • T. Gilbert
  • 7th Life Science

Objective(s) TSW
  • Explain the relationship between traits and
  • Describe the experiments of Gregor Mendel.
  • Explain the difference between dominant and
    recessive traits.

Terms to Learn
  • Heredity the passing of genetic traits from
    parents to offspring
  • Dominant trait the trait observed in the first
    generation when parents that have different
    traits are bred
  • Recessive trait a trait that reappears in the
    second generation after disappearing in the first
    generation when parents with different traits are

Mendel and His Peas
  • Why dont you look like a whale?
  • Simple answer, neither of your parents are
  • But theres more to this answer than meets the
  • Heredity is the passing of traits from parents to
  • Passing of traits is more complicated than you

  • Passing of traits is complicated.
  • You might have curly hair, while both of your
    parents have straight hair.
  • Your eyes may be black, while both your parents
    have brown eyes.
  • How does this happen?
  • This has been studied for years. Gregor Mendel,
    over 150 years ago, performed important
  • His work laid the foundation for finding answers
    to these questions.

Who was Gregor Mendel?
  • Born in 1822 in Austria
  • Entered a monastery at the age of 21
  • Monks taught science and performed many
  • Received formal training in teaching but could
    not pass test.
  • Returned to monastery where he discovered the
    principles of heredity

(No Transcript)
  • Read pages 100-107 in textbooks.
  • As you read, use one of the notetaking strategies
    described on page 100 under Choose Your Own
    Strategy. (Main idea webs, combination notes, or
    mind maps)
  • You may mix and match the strategies.
  • Turn in at the end of class.

Genes are on chromosome pairs.
  • Gene
  • Heredity
  • Allele
  • Homolog
  • Individuals _______ their genes from their

Genes are on chromosome pairs.
  • Genes can occupy a specific location on a
    chromosome and code for a specific characteristic
    or product.
  • Individuals inherit genes from their parents.
  • Most traits are not coded for by one gene.
  • Some characteristics are coded for by many genes.

Genes are on chromosome pairs.
Unraveling the Mystery
  • Working with pea plants, Mendel knew that
    patterns of inheritance were not always clear.
  • For example, sometimes traits that appeared in
    one generation (parents) was not present in the
    next generation (offspring).
  • Mendel noticed these kinds of patterns in
    several other living things, too.

Unraveling the Mystery (cont.)
  • To keep his investigation simple, Mendel decided
    to study only one kind of organism- garden pea
  • Self-Pollinating Peas- Chosen because grow
    quickly, different kinds available,

Self-Pollinating Peas
  • Self-pollinating plant has both male and female
    reproductive structures.
  • Pollen from one flower can fertilize the ovule of
    the same flower or the ovule of another flower
    of the same plant.
  • Why is it important for pea plants to

Self-Pollinating Peas (cont.)
  • Because eggs (in an ovule) and sperm (in pollen)
    from the same plant combine to make a new plant,
    Mendel was able to grow true-breeding plants.
  • True-breeding plant- When it self-pollinates, all
    offspring will have the same trait as the parent.
  • For example, a true-breeding plant with purple
    flowers will always have offspring with purple

Self-Pollinating Peas (cont.)
  • Pea plants can cross-pollinate.
  • In cross-pollination, pollen from one plant
    fertilizes the ovule of a flower on a different
  • Several ways cross-pollination can happen
  • Animals
  • Wind

School to Home Describing Traits
  • How would you describe yourself?
  • Would you say that you are tall or short, have
    curly hair or straight hair?
  • Make a list of some of your physical traits.
  • Make a second list of traits that you were not
    born with, such as caring or good at soccer.
  • Talk to your family about your lists.
  • Do they agree with your descriptions?

  • Mendel studied only one characteristic at a time.
  • Mendel used plants that had different traits for
    each of the characteristics he studied.
  • Characteristic- a feature that has different
    forms in a population. Example- hair color
  • Different forms, such as brown or red hair, are
    called traits.

Mix and Match
  • Mendel was careful to use plants that were true
    breeding for each of the traits being studied.
  • By doing so, Mendel would know what to expect if
    his plants were to self-pollinate.
  • Mendel decided to find out what would happen if
    he bred, or crossed, two plants that had
    different traits of a single characteristic.

Mix and Match (cont.)
  • To be sure the plants cross-pollinated, he
    removed the anthers of one plant so that the
    plant could not self-pollinate.
  • Mendel then used pollen from another plant to
    fertilize the plant.
  • This step allowed Mendel to select which plants
    would be crossed to produce offspring.

Mendels First Experiments
  • Crossed pea plants to study 7 different
  • Each cross, Mendel used plants that were true
    breeding for different traits for each
  • For example, he crossed plants that had purple
    flowers with plants that had white flowers.

Mendels First Experiments (cont.)
  • The offspring from such a cross are called
    first-generation plants.
  • All of the first generation plants in this cross
    had purple flowers.
  • What happened to the trait for white flowers?
  • Mendel got similar results for each cross.
  • One trait was always present in the first
    generation, and the other trait seemed to

Mendels First Experiments (cont.)
  • Mendel chose to call the trait that appeared the
    dominant trait.
  • The other trait seemed to fade into the
    background leading Mendel to call it the
    recessive trait.
  • To find out what happened to the recessive trait,
    Mendel performed another set of experiments.

Mendels Second Experiments
  • Mendel allowed the first-generation plants to
  • Results The recessive trait for white flowers
    reappeared in the second generation.
  • Mendel did this same experiment on each of the 7
  • In each case, some of the second-generation
    plants had the recessive trait.

Ratios in Mendels Experiments
  • Mendel decided to count the number of plants with
    each trait that turned up in the second
    generation in hopes of explaining his results.
  • The recessive trait did not show up as often as
    the dominant trait.
  • Mendel figured out the ratio of dominant to
    recessive traits.
  • A ratio is a relationship between two different
    numbers that is often expressed as a fraction.

Math Practice
  • Calculate the dominant-to-recessive ratio for
    each characteristic.
  • Do you notice anything interesting about the
  • Round to the nearest whole number.
  • Are the ratios all the same, or are they

Gregor Mendel- Gone but Not Forgotten
  • Mendel realized that his results could be
    explained only if each plant had two sets of
    instructions for each characteristic.
  • Each parent would then donate one set of
  • In 1865, Mendel published his findings however,
    his ideas were overlooked or misunderstood until
    approximately 30 years after his death.
  • Once his ideas were rediscovered and understood,
    the door was opened to modern genetics.

  • Heredity is the passing of traits from parents to
  • Gregor Mendel made carefully planned experiments
    using pea plants that could self-pollinate.
  • When parents with different traits are bred,
    dominant traits are always present in the first
    generation. Recessive traits are not visible in
    the first generation but reappear in the second
  • Mendel found a 31 ratio of dominant-to-recessive
    traits in the second generation.