Transcript monohybrid cross.

Chapter 9
Section 1 Mendel’s Legacy
Objectives
• Describe how Mendel was able to control how his pea plants
were pollinated.
• Describe the steps in Mendel’s experiments on true-breeding
garden peas.
• Distinguish between dominant and recessive traits.
• State two laws of heredity that were developed from Mendel’s
work.
• Describe how Mendel’s results can be explained by scientific
knowledge of genes and chromosomes.
Chapter 9
Section 1 Mendel’s Legacy
Gregor Mendel
• The study of how characteristics are transmitted from
parents to offspring is called genetics.
• Mendel is considered to be the “father” of genetics
because of all of his work with heredity
• Heredity is the passing of traits from parents to
their offspring
Chapter 9
Section 1 Mendel’s Legacy
Gregor Mendel, continued
• Mendel’s Garden Peas
– Mendel observed characteristics of pea plants.
– Traits are genetically determined variants of a
characteristic.
– Each characteristic occurred in two contrasting
traits.
Chapter 9
Section 1 Mendel’s Legacy
Gregor Mendel, continued
• Mendel’s Methods
– Self-pollination occurs when pollen is transferred
from the anthers (male) of a plant to the stigma
(female) of the same plant
– Cross-pollination occurs when pollen is
transferred between flowers of two different plants
• Mendel controlled his experiments by manually
pollinating the other plants through cross-pollination, he
removed anthers from the plants he was working with
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Experiments
• Mendel bred plants for several generations that were
true-breeding (self-pollinating) for specific traits and
called these the P generation.
– True breeding pea plants always produce offspring each of
which can have only one form of a trait
– Ex. True-breed pea plants with yellow pods will selfpollinate and produce offspring with yellow pods
• Offspring of the P generation were called the F1
generation.
• Offspring of the F1 generation were called the F2
generation.
Chapter 9
Section 1 Mendel’s Legacy
Three Steps of Mendel’s Experiments
Pg 175 Figure 9-3
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Experiments
Click below to watch the Visual Concept.
Visual Concept
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Results and Conclusions
• Recessive and Dominant Traits
– Mendel concluded that inherited characteristics
are controlled by factors that occur in pairs.
– In his experiments on pea plants, one factor in a
pair masked the other. The trait that masked the
other was called the dominant trait. The trait that
was masked was called the recessive trait.
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Results and Conclusions, continued
• The Law of Segregation
– The law of segregation states that a pair of
factors is segregated, or separated, during the
formation of gametes.
• Law of segregation is used to describe how traits can
disappear and reappear in a certain pattern from
generation to generation
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Results and Conclusions, continued
• The Law of Independent Assortment
– The law of independent assortment states that
factors for individual characteristics are distributed
to gametes independent of one another.
– The law of independent assortment is observed
only for genes that are located on separate
chromosomes or are far apart on the same
chromosome.
Chapter 9
Section 1 Mendel’s Legacy
Support for Mendel’s Conclusions
• We now know that the factors that Mendel studied
are alleles, or alternative forms of a gene.
• One allele for each trait is passed from each parent
to the offspring.
– We can see this by looking at ourselves in
comparison to our parents, we may have some of
both our mother and father
– We will study this further with Punnett Squares in 9-2
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Conclusions
Click below to watch the Visual Concept.
Visual Concept
Homework
SECTION 9.1 REVIEW
PG 178 #1-8
Chapter 9
Section 2 Genetic Crosses
Objectives
• Differentiate between the genotype and the phenotype of an
organism.
• Explain how probability is used to predict the results of genetic
crosses.
• Use a Punnett square to predict the results of monohybrid and
dihybrid genetic crosses.
• Explain how a testcross is used to show the genotype of an
individual whose phenotype expresses the dominant trait.
• Differentiate a monohybrid cross from a dihybrid cross.
Chapter 9
Section 2 Genetic Crosses
Genotype and Phenotype
• The genotype is the genetic makeup of an organism.
• The phenotype is the appearance of an organism.
• Homozygous – when both alleles of a pair are alike
• Heterozygous – when two alleles in a pair are
different
Chapter 9
Section 2 Genetic Crosses
Probability
• Probability is the likelihood that a specific event will
occur.
– Probability equation page 181
• A probability may be expressed as a decimal, a
percentage, or a fraction.
Chapter 9
Section 2 Genetic Crosses
Calculating Probability
Click below to watch the Visual Concept.
Visual Concept
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Monohybrid Crosses
• A Punnett square can be used to predict the
outcome of genetic crosses.
• A cross in which one characteristic is tracked is a
monohybrid cross.
– Figures 9-7 and 9-8 pg 182
• Genotypic ratio is the ratio of genotypes that appear
in offspring
• Phenotypic ratio is the ratio of offspring’s
phenotypes
Chapter 9
Section 2 Genetic Crosses
Punnett Square with Heterozygous Cross
Click below to watch the Visual Concept.
Visual Concept
Chapter 9
Section 2 Genetic Crosses
Monohybrid Cross
of Heterozygous
Plants
Chapter 9
Section 2 Genetic Crosses
Y = Yellow
y = Green (non-yellow)
What is the genotypic ratio
for this monohybrid cross?
What is the phenotypic
ratio for this monohybrid
cross?
Chapter 9
Section 2 Genetic Crosses
Y = Yellow
y = Green (non-yellow)
What is the genotypic ratio
for this monohybrid cross?
1:2:1
What is the phenotypic
ratio for this monohybrid
cross?
3 yellow : 1 green
3:1
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Monohybrid Crosses, continued
• A testcross, in which an individual of unknown
genotype is crossed with a homozygous recessive
individual, can be used to determine the genotype of
an individual whose phenotype expresses the
dominant trait.
Chapter 9
Section 2 Genetic Crosses
Testcross
Click below to watch the Visual Concept.
Visual Concept
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Monohybrid Crosses, continued
• Complete dominance occurs when heterozygous
individuals and dominant homozygous individuals are
indistinguishable in phenotype.
• Ex. Both pea plants PP and Pp for flower color
have purple flowers
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Monohybrid Crosses, continued
• Incomplete dominance occurs when two or more
alleles influence the phenotype and results in a
phenotype intermediate between the dominant trait
and the recessive trait.
• In four o’clock flowers, red flowers (R) self-pollinate and
only produce red offspring, while white flowers (R’) selfpollinate and only produce white offspring
• IF, red (R) and white (R’) are crossed they will produce
100% pink (RR’) offspring
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Monohybrid Crosses, continued
• Codominance occurs when both alleles for a gene
are expressed in a heterozygous offspring.
• Four human ABO blood types, A, B, and AB and O,
are determined by three alleles. The letters A and B
refer to two molecules on the surface of the red
blood cell. The genotype of a person with blood
type AB is IAIB, and neither allele is dominant over
the other type. Type AB blood cells carry both Aand B-types of molecules on their surface.
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Dihybrid Crosses
• A cross in which two characteristics are tracked is a
dihybrid cross.
– To create this type of cross we will use the FOIL
method to be used in a 4x4 Punnett Square
Chapter 9
Section 2 Genetic Crosses
Dihybrid Crosses
Homework
SECTION 9.2 REVIEW
PG 186 #1-7