Download No Slide Title

Chapter 9
Fundamentals of Genetics
Table of Contents
Section 1 Mendel’s Legacy
Section 2 Genetic Crosses
Chapter 9
Section 1 Mendel’s Legacy
Gregor Mendel
• The study of how characteristics are transmitted from parents to
offspring is called genetics.
• Known as the “father of genetics” but not the first person to
study genetics.
• A fair number of practical breeding experiments were done in ancient
times.
• People knew there was a connection between sex and reproduction.
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.
• Every day we observe heritable variations (eyes of brown,
green, blue, or gray) among individuals in a population.
• These traits are transmitted from parents to offspring.
– Each characteristic occurred in two contrasting traits.
– Traits create breeds.
• Another example: dogs were domesticated by 12,000
years ago; selective crossing has given us all the many
breeds we have today
Chapter 9
Section 1 Mendel’s Legacy
Gregor Mendel, continued
• Mendel’s Methods
– Mendel used crosspollination
techniques in which
pollen is transferred
between flowers of
two different plants.
– Studied the traits that
came about.
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Experiments
• Mendel bred plants for several generations that were
true-breeding for specific traits and called these the P
generation.
• 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
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.
• Mendel developed a hypothesis to explain these
results that consisted of four related ideas.
1. Alternative versions of genes (different alleles) account for
variations in inherited characters.
• The purple-flower allele and white-flower allele are two
DNA variations at the flower-color locus.
• 2. For each character, an organism inherits two
alleles, one from each parent.
• In the flower-color example, the F1 plants inherited a
purple-flower allele from one parent and a white-flower
allele from the other
3.If two alleles differ, then one, the dominant allele, is fully expressed in
the the organism’s appearance.
• The other, the recessive allele, has no noticeable effect on the
organism’s appearance.
– Mendel’s F1 plants had purple flowers because the purple-flower
allele is dominant and the white-flower allele is recessive.
4. The two alleles for each character segregate (separate) during gamete
production.
• The separation of alleles into separate gametes is known as Mendel’s
law of segregation.
– If an organism has 2 identical alleles for a particular character, then
that allele exists as a single copy in all gametes.
– If 2 different alleles are present, then 50% (1) of the gametes will
receive one allele and 50% (1) will receive the other.
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.
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.
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Conclusions
Click below to watch the Visual Concept.
Visual Concept
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.
Chapter 9
Section 2 Genetic Crosses
Probability
• Probability is the likelihood that a specific event will
occur.
• 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.
Chapter 9
Section 2 Genetic Crosses
Punnett Square with Homozygous 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
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.
• This is what we have been crossing the last couple
days, traits that had complete dominance.
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.
• This occurs in some flowers. If you cross a red rose
with a white rose, the offspring will all come out PINK!
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.
• This occurs in bulls. When a Roan bull (red colored
fur is crossed with a White bull, all the offspring have
red and white fur.
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Dihybrid Crosses
• A cross in which two
characteristics are
tracked is a
dihybrid cross.
Chapter 12
• Chromosome
– Genes reside on Chromosomes
– Sex chromosomes contain genes that determine
an organism’s sex (gender).
• In mammals, an individual carrying two X
chromosomes is female.
• An individual carrying an X and a Y
chromosome is male.
– The remaining chromosomes that are not directly
involved in determining the sex of an individual are
called autosomes.
Karyotypes: Male and Female
Effects of Gene Location
• Sex-Linked Genes and Traits
– Genes found on the X chromosome are X-linked genes.
– A sex-linked trait is a trait whose allele is located on a sex
chromosome.
– Because males have only one X chromosome, a male who
carries a recessive allele on the X chromosome will exhibit
the sex-linked trait.
• Linked Genes
– Pairs of genes that tend to be inherited together are called
linked genes.
• Chromosome Mapping
– The farther apart two genes are located on a chromosome,
the more likely a cross-over will occur
Mutations
• Germ-cell mutations occur in gametes and can be
passed on to offspring.
• Somatic-cell mutations occur in body
cells and affect only the individual organism.
• Chromosome mutations are changes in the
structure of a chromosome or the loss or gain of an
entire chromosome.
• Gene mutations are changes in one or more of the
nucleotides in a gene.
Chromosome Mutation
Gene Mutation
Ch 12-2
Inheritance of Traits
• Pedigrees
– Geneticists use pedigrees to trace diseases or
traits through families.
– Pedigrees are diagrams that reveal inheritance
patterns of genes.
Pedigree for Cystic Fibrosis
Genetic Traits and Disorders
• Polygenic Inheritance
– Polygenic characters, such as skin color, are
controlled by two or more genes.
• Complex Characters
– Complex characters, such as polygenic traits,
are influenced by both genes and environment.
• Multiple Alleles
– Multiple-allele characters, such as ABO blood
groups, are controlled by three or more alleles of a
gene.
–
(2 visual concepts)
Genetic Traits and Disorders
• X-Linked Traits
– The gene for colorblindness, an X-linked recessive
gene, is found on the X chromosome.
• Sex-influenced Trait
– A sex-influenced trait, such as pattern baldness, is
expressed differently in men than in women even
if it is on an autosome and both sexes have the
same genotype.
–
(Visual concepts)
Treating Genetic Disorders
• Among the treatments are symptom-relieving
treatments and symptom-prevention measures, such
as insulin injections for diabetes.
• Gene Therapy
– In gene therapy, a defective gene is replaced with
a copy of a healthy gene.
– Somatic cell gene therapy alters only body cells.
– Germ cell gene therapy attempts to alter eggs or
sperm.