Preview

1
Chapter 5
Heredity
Preview
Section 1 Mendel and His Peas Section 2 Traits
and Inheritance Section 3 Meiosis
Concept Mapping
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Section 1 Mendel and His Peas
Chapter 5
Bellringer

• You have probably noticed that different people
  have different characteristics, such as eye
  color, hair color, and ear lobes that do or do
  not attach directly to their head. Where do you
  think people get these different traits?
• Record your answers in your science journal.

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Section 1 Mendel and His Peas
Chapter 5
Objectives

• Explain the relationship between traits and
  heredity.
• Describe the experiments of Gregor Mendel.
• Explain the difference between dominant and
  recessive traits.

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Section 1 Mendel and His Peas
Chapter 5
Who Was Gregor Mendel?

• Gregor Mendel was born in 1822 in Heinzendorf,
  Austria.
• At age 21, Mendel entered a monastery. He
  performed many scientific experiments in the
  monastery garden.
• Mendel discovered the principles of heredity,
  the passing of traits from parents to offspring.

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Section 1 Mendel and His Peas
Chapter 5
Unraveling the Mystery

• Mendel used garden pea plants for his
  experiments.
• Self-Pollinating Peas have both male and female
  reproductive structures. So, pollen from one
  flower can fertilize the ovule of the same
  flower.
• When a true-breeding plant self pollinates, all
  of the offspring will have the same trait as the
  parent.

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Section 1 Mendel and His Peas
Chapter 5
Unraveling the Mystery, continued

• Pea plants can also cross-pollinate. Pollen from
  one plant fertilizes the ovule of a flower on a
  different plant.
• Anther male reproductive structure in a plant
• Pollen male reproductive cell in a plant
• Stigma female reproductive structure in a plant
• Ovule female reproductive cell in a plant
• The image below shows
• cross-pollination and
• self-pollination.

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Section 1 Mendel and His Peas
Chapter 5
Unraveling the Mystery, continued

• Characteristics Mendel studied only one pea
  characteristic at a time. A characteristic is a
  feature that has different forms in a population.
• Different forms of a characteristic are called
  traits.

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Section 1 Mendel and His Peas
Chapter 5
Unraveling the Mystery, continued

• Mix and Match Mendel was careful to use plants
  that were true breeding for each of the traits he
  was studying. By doing so, he would know what to
  expect if his plants were to self-pollinate.

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Section 1 Mendel and His Peas
Chapter 5
Mendels First Experiments

• Mendel crossed pea plants to study seven
  different characteristics. (only one per
  experiment)
• Mendel got similar results for each cross. One
  trait was always present in the first generation,
  and the other trait seemed to disappear.
• Mendel called the trait that appeared the
  dominant trait. The trait that seemed to fade
  into the background was called the recessive
  trait.

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Section 1 Mendel and His Peas
Chapter 5
Mendels Second Experiments

• To find out more about recessive traits, Mendel
  allowed the first-generation plants to
  self-pollinate.
• In each case some of the second-generation
  plants had the recessive trait.

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Section 1 Mendel and His Peas
Chapter 5
Mendels Second Experiments, continued

• Ratios in Mendels Experiments The recessive
  trait did not show up as often as the dominant
  trait.
• Mendel decided to figure out the ratio of
  dominant traits to recessive traits.

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Section 1 Mendel and His Peas
Chapter 5
Mendels Second Experiments, continued
In all cases the ratio was about 31 dominant
recessive.
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Section 1 Mendel and His Peas
Chapter 5
Mendels Second Experiments, continued

• 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.
• Mendels work opened the door to modern genetics.

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Critical Aspects of Mendels Experiments

• Each characteristic that he studied had only 2
  forms/traits
• He used true-breeding populations of pea plants
• His pea plants could self-pollinate AND
  cross-pollinate

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Section 2 Traits and Inheritance
Chapter 5
Bellringer

• If you flip a coin, what are the chances that it
  will land on heads? tails? Suppose that you
  flipped the coin and got heads. What are the
  chances that you will get heads again?
• Record your answers in your science journal.

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Section 2 Traits and Inheritance
Chapter 5
Objectives

• Explain how genes and alleles are related to
  genotype and phenotype.
• Use the information in a Punnett square.
• Explain how probability can be used to predict
  possible genotypes in offspring.
• Describe three exceptions to Mendels
  observations.

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Section 2 Traits and Inheritance
Chapter 5
A Great Idea

• Mendel knew that there must be two sets of
  instructions for each characteristic.
• The instructions for an inherited trait are
  called genes.
• The different forms (often dominant and
  recessive) of a gene are alleles.
• Phenotype An organisms appearance is known as
  its phenotype. Genes affect the phenotype.

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Section 2 Traits and Inheritance
Chapter 5
A Great Idea, continued

• Genotype The combination of inherited alleles
  together form an organisms genotype.
• Punnett Squares are used to organize all the
  possible genotype combinations of offspring from
  particular parents.

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Section 2 Traits and Inheritance
Chapter 5
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Section 2 Traits and Inheritance
Chapter 5
What Are the Chances?

• Probability is the mathematical chance that
  something will happen.
• Probability is most often written as a fraction
  of percentage.

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Section 2 Traits and Inheritance
Chapter 5
Calculating Probability
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Section 2 Traits and Inheritance
Chapter 5
What Are the Chances?, continued

• Genotype Probability To have white flowers, a
  pea plant must receive a p allele from each
  parent. Each offspring of a Pp Pp cross has a 50
  chance of receiving either allele from either
  parent. So, the probability of inheriting two p
  alleles is 1/2 ? 1/2, which equals 1/4, or 25.

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Section 2 Traits and Inheritance
Chapter 5
More About Traits

• Incomplete Dominance Researchers have found
  that sometimes one trait is not completely
  dominant over another.
• One Gene, Many Traits Sometimes one gene
  influences more than one trait.
• Many Genes, One Trait Some traits, such as the
  color of your skin, hair, and eyes, are the
  result of several genes acting together.

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Section 2 Traits and Inheritance
Chapter 5
More About Traits, continued

• The Importance of Environment Genes arent the
  only influences on traits. A combination of
  things determine an individuals characteristics.
• Your environment also influences how you grow.
• Lifestyle choices can also affect a persons
  traits.

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Section 3 Meiosis
Chapter 5
Bellringer

• Write a sentence to describe each of the
  following terms heredity, genotype, and
  phenotype. Note how genotype and phenotype are
  related, and how they are different. Is heredity
  necessarily a factor in both genotype and
  phenotype? Why or why not?
• Record your answers in your science journal.

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Section 3 Meiosis
Chapter 5
Objectives

• Explain the difference between mitosis and
  meiosis.
• Describe how chromosomes determine sex.
• Explain why sex-linked disorders occur in one
  sex more often than in the other.
• Interpret a pedigree.

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Section 3 Meiosis
Chapter 5
Asexual Reproduction

• In asexual reproduction, only one parent cell is
  needed. The structures inside the cell are
  copied, and then the parent cell divides, making
  two exact copies.
• This type of cell reproduction is called
  mitosis. Most of the cells in your body and most
  single-celled organisms reproduce this way.

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Section 3 Meiosis
Chapter 5
Mitosis
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Section 3 Meiosis
Chapter 5
Sexual Reproduction

• In sexual reproduction, two parent cells (sex
  cells) join together to form offspring that are
  different from both parents.
• Chromosomes that carry the same sets of genes
  are called homologous chromosomes.
• Each sex cell has only one of the chromosomes
  from the homologous pair.

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Section 3 Meiosis
Chapter 5
Sexual Reproduction, continued

• Meiosis Sex cells are made during meiosis.
• Meiosis is a copying process that produces cells
  with half the usual number of chromosomes.

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Section 3 Meiosis
Chapter 5
Meiosis
Click below to watch the Visual Concept.
Visual Concept
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Section 3 Meiosis
Chapter 5
Sexual Reproduction, continued

• Genes and Chromosomes Walter Sutton studied
  meiosis in sperm cells in grasshoppers.
• Using his observations and his knowledge of
  Mendels work, Sutton proposed that
• Genes are located on chromosomes.

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Section 3 Meiosis
Chapter 5
The Steps of Meiosis

• During meiosis, chromosomes are copied once, and
  then the nucleus divides twice.
• The resulting sex cells (sperm and eggs) have
  half the number of chromosomes of a normal body
  cell.

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Section 3 Meiosis
Chapter 5
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Section 3 Meiosis
Chapter 5
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Section 3 Meiosis
Chapter 5
Meiosis and Mendel

• The steps of meiosis explain Mendels results.
  The following slide shows what happens to a pair
  of homologous chromosomes during meiosis and
  fertilization.

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Section 3 Meiosis
Chapter 5
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Section 3 Meiosis
Chapter 5
Meiosis and Mendel, continued

• Sex Chromosomes carry genes that determine sex.
• Human females have two X chromosomes.
• Human males have one X chromosome and one Y
  chromosome.

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Section 3 Meiosis
Chapter 5
Meiosis and Mendel, continued

• Sex-Linked Disorders The genes for certain
  disorders, such as colorblindness, are carried on
  the X chromosome.
• Genetic Counseling Genetic counselors use
  pedigrees to trace traits through generations of
  a family. These diagrams can often predict if a
  person is a carrier of a hereditary disease.
• Selective Breeding In selective breeding,
  organisms with desirable characteristics are
  mated.

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Heredity
Chapter 5
Concept Mapping
Use the terms below to complete the Concept
Mapping on the next slide.
alleles parents phenotype genes offspring genotype characteristics dominant

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Heredity
Chapter 5
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Heredity
Chapter 5