Unit 6 Lesson 4 Heredity
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Unit 6 Lesson 4 Heredity
Florida Benchmarks
• SC.7.L.16.1 Understand and explain that every
organism requires a set of instructions that
specifies its traits, that this hereditary information
(DNA) contains genes located in the chromosomes
of each cell, and that heredity is the passage of
these instructions from one generation to another.
• HE.6.C.1.4 Recognize how heredity can affect
personal health.
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Unit 6 Lesson 4 Heredity
Give Peas a Chance
What is heredity?
• Traits, such as hair color, result from the
information stored in genetic material.
• Heredity is the passing of genetic material from
parents to offspring.
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Unit 6 Lesson 4 Heredity
What did Gregor Mendel discover about
heredity?
• Gregor Mendel was an Austrian monk. In the
1800s, Mendel did the first major experiments in
heredity.
• Mendel studied seven characteristics of pea
plants.
• A characteristic is a feature that has different
forms in a population.
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Unit 6 Lesson 4 Heredity
What did Gregor Mendel discover about
heredity?
• The seven different characteristics Mendel studied
were plant height, flower and pod position, seed
shape, seed color, pod shape, pod color, and
flower color.
• Each characteristic had two different forms. These
different forms are called traits.
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Unit 6 Lesson 4 Heredity
What did Gregor Mendel discover about
heredity?
• Mendel always started with plants that were truebreeding.
• True-breeding plants always produce offspring
with the same characteristic if allowed to selfpollinate naturally.
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Unit 6 Lesson 4 Heredity
What did Gregor Mendel discover about
heredity?
• Mendel crossed plants that were true-breeding for
producing yellow seed pods with plants that were
true-breeding for green seed pods.
• All of the plants from the first generation
produced green seed pods.
• Mendel called the green seed pod the dominant
trait, and the yellow seed pods the recessive trait.
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Unit 6 Lesson 4 Heredity
What did Gregor Mendel discover about
heredity?
• Next, Mendel let the first generation plants selfpollinate.
• Out of the generation that resulted, called the
second generation, about three-fourths had green
seed pods and one-fourth had yellow pods.
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Unit 6 Lesson 4 Heredity
What did Gregor Mendel discover about
heredity?
• The recessive trait had seemed to disappear in the
first generation, but it reappeared in the second
generation.
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Unit 6 Lesson 4 Heredity
What did Gregor Mendel discover about
heredity?
• Mendel hypothesized that each plant must have
two heritable “factors” for each trait, one from
each parent.
• Some traits, such as yellow color, could only be
observed if a plant had two of the same factors.
• A plant with two different factors would show the
dominant factor but be able to pass on both
factors to its offspring.
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Unit 6 Lesson 4 Heredity
It’s in your genes!
How are traits inherited?
• Mendel’s ideas can be even further explained by
our modern understanding of DNA.
• What Mendel called “factors” are actually
segments of DNA known as genes.
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Unit 6 Lesson 4 Heredity
How are traits inherited?
• Genes are segments of DNA. They give
instructions for producing a certain characteristic.
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Unit 6 Lesson 4 Heredity
How are traits inherited?
• The offspring has two versions of the same gene
for every characteristic—one from each parent.
• Different versions of a gene are known as alleles.
• Dominant alleles are shown with a capital letter,
and recessive alleles are shown with a lowercase
version of the same letter.
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Unit 6 Lesson 4 Heredity
How are traits inherited?
• An organism with one dominant and one recessive
allele for a gene is heterozygous for that gene.
• An organism with two of the same alleles for a
gene is homozygous for that gene.
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Unit 6 Lesson 4 Heredity
How are traits inherited?
• The combination of alleles that you inherited from
your parents is your genotype.
• Your observable traits make up your phenotype.
• The phenotypes of some traits follow patterns
similar to the ones Mendel discovered.
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Unit 6 Lesson 4 Heredity
How are traits inherited?
• The dominant allele contributes to the phenotype
if one or two copies are present in the genotype.
• The recessive allele contributes to the phenotype
only when two copies of it are present.
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Unit 6 Lesson 4 Heredity
How are traits inherited?
• If one chromosome in the pair contains a
dominant allele and the other contains a recessive
allele, the dominant allele determines the
phenotype.
• This is called complete dominance.
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Unit 6 Lesson 4 Heredity
How are traits inherited?
• Some characteristics are a result of several genes
acting together.
• Sometimes, one gene influences more than one
trait.
• For example, many genetic disorders, such as
sickle-cell anemia, are linked to a single gene but
affect many traits.
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Unit 6 Lesson 4 Heredity
How are traits inherited?
• Sometimes, the environment can influence an
organism’s phenotype.
• Some traits are acquired only from one’s
environment and are not inherited.
• For example, your ability to read and write is an
acquired trait.
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Unit 6 Lesson 4 Heredity
Bending the Rules
What are the exceptions to complete
dominance?
• Some traits do not follow the pattern of complete
dominance.
• For traits that show incomplete dominance and
codominance, one trait is not completely dominant
over another.
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Unit 6 Lesson 4 Heredity
What are the exceptions to complete
dominance?
• In incomplete dominance, each allele in a
heterozygous individual influences the phenotype.
• The result of incomplete dominance is a
phenotype that is a blend of the phenotypes of the
parents.
• An example of this in humans is hair. A person
with one allele for straight hair and one allele for
curly hair will have wavy hair.
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Unit 6 Lesson 4 Heredity
What are the exceptions to complete
dominance?
• For a trait that shows codominance, both of the
alleles in a heterozygous individual contribute to
the phenotype.
• Heterozygous individuals have both of the traits
associated with their two alleles.
• Human blood type is an example of codominance.
Three alleles play a role in determining blood
type.
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Unit 6 Lesson 4 Heredity
What are the exceptions to complete
dominance?
• Human blood type is an example of codominance.
• Three alleles play a role in determining blood
type.
• A person with an A allele and a B allele has type
AB blood.
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