Download Unit 2 Lesson 4 Heredity Essential Question: How are traits inherited

Big Idea: Characteristics from parents are
passed to offspring in predictable ways
Unit 2 Lesson 4 Heredity
Essential Question: How are traits inherited?
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 4 Heredity
P124
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.
What did Gregor Mendel discover about heredity?
•Gregor Mendel was an
Austrian monk. In the
1800s, Mendel performed
the first major experiments
in heredity.
Unit 2 Lesson 4 Heredity
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What did Gregor Mendel discover about heredity?
• Mendel studied seven
characteristics of pea plants.
•
plant height, flower and pod
position, seed shape, seed
color, pod shape, pod color,
and flower color.
• A characteristic is a feature
that has different forms in a
population.
• Each characteristic had two
different forms.
• These different forms are called
traits.
Is flower color a
characteristic or a trait?
Characteristic
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What did Gregor Mendel discover about heredity?
• Mendel studied each characteristic separately, always
starting with plants that were true-breeding.
• True-breeding plants always produce offspring with the
same trait if allowed to self-pollinate naturally.
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What did Gregor Mendel discover about heredity?
• Mendel crossed plants that were true-breeding for
producing yellow seed pods with plants that were truebreeding 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 pod the recessive trait.
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What did Gregor Mendel discover about heredity?
• Next, Mendel let the first generation plants self-pollinate.
• Out of the generation that resulted, called the second
generation, about three-fourths had green seed pods
and one-fourth had yellow pods.
• The recessive trait had seemed to disappear in the first
generation, but it reappeared in the second generation.
Unit 2 Lesson 4 Heredity
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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 (Recessive), 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.
Unit 2 Lesson 4 Heredity
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It’s in Your Genes!
How are traits inherited?
1) Genes are passed from parent to offspring
2) Genes Influence Traits
3) Many Genes can influence a single trait
4) Single gene can influence many traits
5) Environment can Influence Traits
Unit 2 Lesson 4 Heredity
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It’s in Your Genes!
1) Genes are passed
from parent to
offspring
How are traits inherited?
• Mendel’s ideas can be further explained by our modern
understanding of DNA.
• What Mendel called “factors” are actually segments of DNA
known as genes.
• Genes are segments of DNA. They give instructions for
producing a certain characteristic
1) Genes are passed
P126
from parent to
How are traits inherited? offspring
Unit 2 Lesson 4 Heredity
• 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.
• 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.
Unit 2 Lesson 4 Heredity
P127 2) Genes Influence Traits
How are traits inherited?
• The combination of alleles that you inherited from
your parents is your genotype.
• Your observable traits make up your phenotype.
Unit 2 Lesson 4 Heredity
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2) Genes Influence Traits
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.
Unit 2 Lesson 4 Heredity
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2) Genes Influence Traits
How are traits inherited?
Unit 2 Lesson 4 Heredity
P127 2) Genes Influence Traits
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.
complete dominance.
3) Many Genes can
influence a single
How are traits inherited?
trait
Unit 2 Lesson 4 Heredity
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• Some characteristics are a result of several genes acting
together.
• Different combinations of alleles can result in different
shades of eye color or even skin color.
Unit 2 Lesson 4 Heredity
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How are traits inherited?
4) Single gene can
influence many
traits
• Sometimes, one gene influences more than one trait.
Vision and Skin
problems
many genetic disorders, such as sickle cell anemia, are
linked to a single gene but affect many traits.
Protein in RBC
Damage spleen
Not able to deliver
oxygen to organs
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How are traits inherited?
5) Environment
can Influence
Traits
• Sometimes, the environment can influence an organism’s
phenotype.
• Arctic fox gene (protein) reacts to
amount of sunlight.
• Traits that are learned in one’s environment are not
inherited.
•
Learn how to read, write, play basketball
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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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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.
Unit 2 Lesson 4 Heredity
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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.
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What are the exceptions to complete
dominance?
• Human blood type is an example of codominance.
• Three alleles, called A, B, and O, play a role in determining
blood type.
• A person with an A allele and a B allele has type AB blood.