PowerPoint PresentationCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
From PowerPoint® Lectures for Biology: Concepts & Connections
CHAPTER 9
Mendel’s principles are valid for all sexually reproducing species
However, often the genotype does not dictate the phenotype in the simple way his principles describe
VARIATIONS ON MENDEL’S PRINCIPLES
9.11 The relationship of genotype to phenotype is rarely simple
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9.12 Incomplete dominance results in intermediate phenotypes
When an offspring’s phenotype—such
as flower color— is
in between the phenotypes of its parents, it exhibits incomplete dominance
P GENERATION
F1 GENERATION
F2 GENERATION
Incomplete dominance in human hypercholesterolemia
Figure 9.12B
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9.13 Many genes have more than two alleles in the population
In a population, multiple alleles often exist for a characteristic
The three alleles for ABO blood type in humans is an example
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The alleles for A and B blood types are codominant, and both are expressed in the phenotype
Figure 9.13
Blood
Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left
O
A
B
AB
A
B
AB
ii
This is called pleiotropy
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Individual homozygous
Sickle cells
Clumping of cells
and clogging of
small blood vessels
9.15 Connection: Genetic testing can detect disease-causing alleles
Genetic testing can be of value to those at risk of developing a genetic disorder or of passing it on to offspring
Figure 9.15B
Figure 9.15A
Dr. David Satcher, former U.S. surgeon general, pioneered screening for sickle-cell disease
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9.16 A single characteristic may be influenced by many genes
This situation creates a continuum of phenotypes
Example: skin color
Figure 9.16
P GENERATION
F1 GENERATION
F2 GENERATION
Genes are located on chromosomes
Their behavior during meiosis accounts for inheritance patterns
THE CHROMOSOMAL BASIS OF INHERITANCE
9.17 Chromosome behavior accounts for Mendel’s principles
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The chromosomal basis of Mendel’s principles
Figure 9.17
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9.18 Genes on the same chromosome tend to be inherited together
Certain genes are linked
They tend to be inherited together because they reside close together on the same chromosome
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Figure 9.18
9.19 Crossing over produces new combinations of alleles
This produces gametes with recombinant chromosomes
The fruit fly Drosophila melanogaster was used in the first experiments to demonstrate the effects of crossing over
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A
B
a
b
Tetrad
Figure 9.19C
9.20 Geneticists use crossover data to map genes
Crossing over is more likely to occur between genes that are farther apart
Recombination frequencies can be used to map the relative positions of genes on chromosomes
g
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Alfred H. Sturtevant, seen here at a party with T. H. Morgan and his students, used recombination data from Morgan’s fruit fly crosses to map genes
Figure 9.20A
Figure 9.20C
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A human male has one X chromosome and one Y chromosome
A human female has two X chromosomes
Whether a sperm cell has an X or Y chromosome determines the sex of the offspring
SEX CHROMOSOMES AND SEX-LINKED GENES
9.21 Chromosomes determine sex in many species
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Figure 9.21A
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Other systems of sex determination exist in other animals and plants
Figure 9.21B-D
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9.22 Sex-linked genes exhibit a unique pattern of inheritance
All genes on the sex chromosomes are said to be sex-linked
In many organisms, the X chromosome carries many genes unrelated to sex
Fruit fly eye
color is a
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Their inheritance pattern reflects the fact that males have one X chromosome and females have two
Figure 9.22B-D
These figures illustrate inheritance patterns for white eye color (r) in the fruit fly, an X-linked recessive trait
Female
Male
Female
Male
Female
Male
XrY
XRXR
XRXr
XRY
XR
Xr
Y
XRXr
XR
Xr
XRXR
XR
Y
XRY
XrXR
XRY
XrY
XRXr
XR
Xr
Xr
Y
XRXr
XrXr
XRY
XrY
XrY
9.23 Connection: Sex-linked disorders affect mostly males
Most sex-linked human
These are mostly seen in males
A male receives a single X-linked allele from his mother, and will have the disorder, while a female has to receive the allele from both parents to be affected
Figure 9.23A
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A high incidence of hemophilia has plagued the royal families of Europe
Figure 9.23B