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Chapter 19
Heredity
Table of Contents
Section 1 Mendel and His Peas
Section 2 Traits and Inheritance
Section 3 Meiosis
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Chapter 19
Section 1 Mendel and His Peas
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? How do you think they
are passed from one generation to the next?
Record your answers in your science journal.
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Chapter 19
Section 1 Mendel and His Peas
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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Chapter 19
Section 1 Mendel and His Peas
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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Chapter 19
Section 1 Mendel and His Peas
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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Chapter 19
Section 1 Mendel and His Peas
Unraveling the Mystery, continued
• Pea plants can also cross-pollinate. Pollen from one
plant fertilizes the ovule of a flower on a different
plant.
• The image below shows cross-pollination and selfpollination.
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Chapter 19
Section 1 Mendel and His Peas
Unraveling the Mystery, continued
• Characteristics and
Traits of Pea Plants
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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Chapter 19
Section 1 Mendel and His Peas
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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Chapter 19
Section 1 Mendel and His Peas
Mendel’s First Experiments
• Mendel crossed pea plants to study seven different
characteristics.
• 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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Chapter 19
Section 1 Mendel and His Peas
Mendel’s Second
Experiments
• To find out more about
recessive traits, Mendel
allowed the firstgeneration plants to selfpollinate.
• In each case some of the
second-generation plats
had the recessive trait.
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Chapter 19
Section 1 Mendel and His Peas
Mendel’s Second Experiments, continued
• Ratios in Mendel’s 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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Chapter 19
Section 1 Mendel and His Peas
Mendel’s Second Experiments, continued
In all cases the
ratio was about
3:1 dominant :
recessive.
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Chapter 19
Section 1 Mendel and His Peas
Mendel’s 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.
• Mendel’s work opened the door to modern
genetics.
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Chapter 19
Section 2 Traits and Inheritance
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? What are the chances you will get
heads two times in a row? five times?
Record your answers in your science journal.
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Chapter 19
Section 2 Traits and Inheritance
Objectives
• Explain how genes and alleles are related to
genotype and phenotype.
• Describe how the information in a Punnett square
predicts possible genotypes.
• Explain how probability can be used to predict
possible genotypes.
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Chapter 19
Section 2 Traits and Inheritance
Objectives, continued
• Describe how interactions between genes can
allow for a variety of traits in offspring.
• Describe how the environment can influence traits.
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Chapter 19
Section 2 Traits and Inheritance
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.
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Chapter 19
Section 2 Traits and Inheritance
A Great Idea, continued
• Dominance occurs when certain alleles mask the
expression of other alleles.
• A recessive trait or allele is expressed only when
two recessive alleles for the same characteristic
are inherited.
• Phenotype An organism’s appearance is known
as its phenotype. Genes affect the phenotype.
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Chapter 19
Section 2 Traits and Inheritance
A Great Idea, continued
• Genotype The combination of inherited alleles
together form an organism’s genotype.
• A plant with two dominant or two recessive
alleles is said to be homozygous.
• A plant that has the genotype Pp is said to be
heterozygous.
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Chapter 19
Section 2 Traits and Inheritance
A Great Idea, continued
• Punnett Squares are used to organize all the
possible genotype combinations of offspring from
particular parents.
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Chapter 19
Section 2 Traits and Inheritance
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Chapter 19
Section 2 Traits and Inheritance
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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Chapter 19
Section 2 Traits and Inheritance
Calculating Probability
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Chapter 19
Section 2 Traits and Inheritance
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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Chapter 19
Section 2 Traits and Inheritance
Gene Interactions and Variations
• 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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Chapter 19
Section 2 Traits and Inheritance
The Importance of Environment
• Genes aren’t the only influences on traits. A
combination of things determine an individual’s
characteristics.
• Your environment also influences how you grow.
• Lifestyle choices can also affect a person’s traits.
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Chapter 19
Section 3 Meiosis
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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Chapter 19
Section 3 Meiosis
Objectives
• Describe the patterns and advantages of asexual
reproduction in animals and plants.
• Describe the patterns and advantages of sexual
reproduction in animals and plants.
• Differentiate between mitosis and meiosis.
• Explain how the process of meiosis relates to the
passing of traits from parent to offspring.
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Chapter 19
Section 3 Meiosis
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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Chapter 19
Section 3 Meiosis
Mitosis
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Chapter 19
Section 3 Meiosis
Asexual Reproduction, continued
• Advantages of Asexual Reproduction One
advantage of asexual reproduction is that organisms
can produce many offspring in a relatively short
amount of time.
• An advantage for animals that reproduce asexually
is that they do not have to use energy to find a
mate.
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Chapter 19
Section 3 Meiosis
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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Chapter 19
Section 3 Meiosis
Sexual Reproduction, continued
• Advantages of Sexual Reproduction The
combination of genetic information during
sexual reproduction allows for variation among
a population.
• The variation of genes allows a population to
adapt to changes in the environment over time.
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Chapter 19
Section 3 Meiosis
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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Chapter 19
Section 3 Meiosis
Meiosis
Click below to watch the Visual Concept.
You may stop the video at any time by pressing
the Esc key.
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Chapter 19
Section 3 Meiosis
Sexual Reproduction, continued
• Genes and Chromosomes Walter Sutton
studied meiosis in sperm cells in grasshoppers.
• Using his observations and his knowledge of
Mendel’s work, Sutton proposed that:
Genes are located on chromosomes.
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Chapter 19
Section 3 Meiosis
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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Chapter 19
Section 3 Meiosis
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Chapter 19
Section 3 Meiosis
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Chapter 19
Section 3 Meiosis
Meiosis and Fertilization
• The next slide shows what happens to a pair of
homologous chromosomes during meiosis and
fertilization. The cross shown is between a plant
that is homozygous for round seeds (dominant
trait) and a plant that is homozygous for wrinkled
seeds (recessive trait).
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Chapter 19
Section 3 Meiosis
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Chapter 19
Section 3 Meiosis
Meiosis and Fertilization, 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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Chapter 19
Section 3 Meiosis
Meiosis and Fertilization, 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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Chapter 19
Heredity
Concept Mapping
Use the terms below to complete the concept map on
the next slide.
meiosis
eggs
cell division
sperm
X chromosome
mitosis
Y chromosome
sex cells
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Chapter 19
Heredity
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Chapter 19
Heredity
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End of Chapter 19 Show
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Chapter 19
Standardized Test Preparation
FCAT
For the following questions, write your answers on a
separate sheet of paper.
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Chapter 19
Standardized Test Preparation
1. A peach tree has been bred to produce more
peaches. While the peach crop from the tree has
been considerably larger, the tree has also
become susceptible to a disease that will
eventually kill it. If this tree is self-pollinating, what
is the chance that seedlings from this tree will also
be susceptible to the disease?
A. 25%
B. 50%
C. 75%
D. 100%
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Chapter 19
Standardized Test Preparation
1. A peach tree has been bred to produce more
peaches. While the peach crop from the tree has
been considerably larger, the tree has also
become susceptible to a disease that will
eventually kill it. If this tree is self-pollinating, what
is the chance that seedlings from this tree will also
be susceptible to the disease?
A. 25%
B. 50%
C. 75%
D. 100%
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Standardized Test Preparation
2. Caroline has two lilies in her garden. She wants to
see if she can produce offspring that will have
traits of both lilies. Which of the following
structures will Caroline have to remove from the
plant she is pollinating to ensure that crosspollination occurs?
F. the anthers
G. the ovule
H. the petals
I. the stigma
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Standardized Test Preparation
2. Caroline has two lilies in her garden. She wants to
see if she can produce offspring that will have
traits of both lilies. Which of the following
structures will Caroline have to remove from the
plant she is pollinating to ensure that crosspollination occurs?
F. the anthers
G. the ovule
H. the petals
I. the stigma
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Standardized Test Preparation
3. Juanita visited a friend’s farm. At the farm she
noticed a calf with a mixture of brown and white
fur. The calf’s father had brown fur and the calf’s
mother had white fur. What principle of heredity
can explain why the calf had a mixture of brown
and white fur?
A. cross-pollination
B. selective breeding
C. incomplete dominance
D. environmental influence
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3. Juanita visited a friend’s farm. At the farm she
noticed a calf with a mixture of brown and white
fur. The calf’s father had brown fur and the calf’s
mother had white fur. What principle of heredity
can explain why the calf had a mixture of brown
and white fur?
A. cross-pollination
B. selective breeding
C. incomplete dominance
D. environmental influence
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Standardized Test Preparation
4. Organisms reproduce either asexually or sexually.
In asexual reproduction, there is only one parent
and the offspring are genetically identical to the
parent. In sexual reproduction, there are two
parents and the offspring inherit traits from both
parents. How is the process of cell division in
asexual reproduction different than the process of
cell division in sexual reproduction?
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Standardized Test Preparation
Question 4, continued
Full credit answers should include the following points:
Students should explain that asexual reproduction is
referred to as mitosis and that sexual reproduction is
referred to as meiosis. Students should explain that the
main difference between the two processes is the
number of times the cell divides and the resulting number of chromosomes in each final cell. In mitosis
the cell divides one time and both of these cells have
the same number of chromosomes as the parent cell. In
meiosis the cell divides two times and each of the four
resulting cells has half the number of chromosomes as
the parent cell.
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Chapter 19
Standardized Test Preparation
5. Chad created the pedigree diagram shown below
to show the occurrence of sickle cell anemia in his
family. Sickle cell anemia is a recessive disease
(ss) that affects the ability of red blood cells to
carry oxygen. Those who do not carry the gene are
noted as (SS). According to the diagram, Chad is
one of five children. Both a brother and a sister do
not carry the gene for the disease. One of his
sisters has the disease.
Continued on the slide
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Standardized Test Preparation
Question 5, continued
5. Which of the following are the genotypes of Chad’s
parents?
F. Ss and SS
G. Ss and Ss
H. ss and ss
I. ss and SS
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Question 5, continued
5. Which of the following are the genotypes of Chad’s
parents?
F. Ss and SS
G. Ss and Ss
H. ss and ss
I. ss and SS
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6. Traits vary from person to person. Two traits
include straight hair and curly hair. Curly hair is the
dominant trait (WW), while straight hair is the
recessive trait (ww). If a man with straight hair
(WW) and a woman with curly hair (ww) have
children, what percentage of their children will
have straight hair?
Complete the Punnett square below to show the
possible genotypes for the children.
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Standardized Test Preparation
6. Complete the Punnett square below to show the
possible genotypes for the children.
w
w
W
Ww
Ww
W
Ww
Ww
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Chapter 19
Section 1 Mendel and His Peas
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Chapter 19
Section 1 Mendel and His Peas
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Chapter 19
Section 1 Mendel and His Peas
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Chapter 19
Section 1 Mendel and His Peas
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Chapter 19
Section 1 Mendel and His Peas
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Chapter 19
Section 2 Traits and Inheritance
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Chapter 19
Section 3 Mitosis
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Chapter 19
Section 3 Mitosis
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Chapter 19
Standardized Test Preparation
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