Download Ch 4 : Heredity

Chapter 4
Section 1 Mendel and His Peas
Objectives
Content
Explain the relationship between traits and heredity.
Explain the difference between dominant and
recessive traits.
Language
Describe the experiments of Gregor Mendel.
Chapter 4
What is Heredity?
Who discovered it?
Chapter 4
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.
Chapter 4
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.
Chapter 4
Section 1 Mendel and His Peas
• Pea plants can also cross-pollinate.
Pollen from one plant fertilizes the ovule
of a flower on a different plant.
• The image below shows crosspollination and self-pollination.
Chapter 4
Section 1 Mendel and His Peas
• 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.
Chapter 4
Section 1 Mendel and His Peas
• 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.
Chapter 4
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.
Chapter 4
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.
Chapter 4
Section 1 Mendel and His Peas
Mendel’s Second
Experiments
• To find out more about recessive traits,
Mendel allowed the first-generation
plants to self-pollinate.
• In each case some of the secondgeneration plants had the recessive trait.
Chapter 4
Section 1 Mendel and His Peas
• 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.
Chapter 4
In all cases the ratio
was about ____:____
dominant : recessive.
Chapter 4
Section 1 Mendel and His Peas
Mendel’s Second Experiments
• 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.
Chapter 4
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?
Record your answers in your science journal.
Chapter 4
Section 2 Traits and Inheritance
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 Mendel’s
observations.
Chapter 4
Section 2 Traits and Inheritance
Genes are found on the chromosomes(DNA) of an
individual. Genes are the instructions for an inherited
trait.
The different forms (often dominant or recessive) of a
gene are alleles.
Pea plants have a gene for flower color, the alleles
are either purple(Dominant) or white(recessive)
Chapter 4
Section 2 Traits and Inheritance
Genotype The combination of inherited alleles together form
an organism’s genotype.
We use letters to represent the Alleles of a genotype
•The letter is chosen based on the name of the dominant
trait
•Capitol letter for a dominant allele
•Lowercase letter for a recessive allele
•Ex: Purple flowers is a dominant trait in pea plants so we
use a capitol P for Dominant and a lower case p for
Recessive
•Chromosomes work in pairs so you have two copies of
each allele resulting in three possible genotypes
Chapter 4
Possible Genotypes Ex : Flower color in peas
 Homozygous Dominant (PP)
 Both alleles are dominant
 Homozygous Recessive (pp)
 Both alleles are recessive
 Heterozygous (Pp)
 One dominant and one recessive allele
Chapter 4
Phenotype is an organism appearance due to its genotype
Different Genotypes result in different Phenotypes
Homozygous Dominant will show the Dominant Phenotype
Homozygous Recessive will show the Recessive Phenotype
Heterozygous will show the Dominant Phenotype
PP =
pp =
Pp=
Chapter 4
Punnett Squares are used to organize all the possible
genotype combinations of offspring from particular
parents.
Chapter 4
Section 2 Traits and Inheritance
Chapter 4
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.
Chapter 4
Section 2 Traits and Inheritance
Calculating Probability
Chapter 4
Section 2 Traits and Inheritance
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.
Chapter 4
Section 2 Traits and Inheritance
More About Traits, continued
• 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.