© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
PowerPoint Lectures forCampbell Biology: Concepts & Connections, Seventh EditionReece, Taylor, Simon, and Dickey
Chapter 9Chapter 9 Patterns of Inheritance
Figure 9.0_1Chapter 9: Big Ideas
Mendel’s Laws Variations onMendel’s Laws
The Chromosomal Basisof Inheritance
Sex Chromosomes andSex-Linked Genes
9.5 The law of independent assortment is revealed by tracking two characters at once
The following figure demonstrates the law of independent assortment as it applies to two characters in Labrador retrievers:
– black versus chocolate color,
– normal vision versus progressive retinal atrophy.
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Figure 9.5B
Phenotypes
Genotypes
Black coat,normal vision
B_N_
Black coat,blind (PRA)B_nn
Blind
Chocolate coat,normal vision
bbN_
Blind
Blind Blind
Chocolate coat,blind (PRA)
bbnn
Mating of double heterozygotes (black coat, normal vision)BbNn BbNn
Phenotypic ratioof the offspring
9Black coat,
normal vision
3Black coat,blind (PRA)
1Chocolate coat,
blind (PRA)
3Chocolate coat,normal vision
Figure 9.5B_1
Phenotypes
Genotypes
Phenotypes
Genotypes
Blind
Blind
Black coat,normal vision
B_N_
Black coat,blind (PRA)B_nn
Chocolate coat,normal vision
bbN_
Chocolate coat,blind (PRA)bbnn
Figure 9.5B_2
Blind Blind
Mating of double heterozygotes (black coat, normal vision)
BbNn BbNn
Phenotypic ratio of the offspring
9Black coat,
normal vision
3Black coat,blind (PRA)
1Chocolate coat,
blind (PRA)
3Chocolate coat,normal vision
9.7 Mendel’s laws reflect the rules of probability
Using his strong background in mathematics, Mendel knew that the rules of mathematical probability affected
– the segregation of allele pairs during gamete formation and
– the re-forming of pairs at fertilization.
The probability scale ranges from 0 to 1. An event that is
– certain has a probability of 1 and
– certain not to occur has a probability of 0.
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Evaluating Results Mendel was unable to analyze mathematically how well
the actual outcome of his crosses fulfilled his predictions.
– Karl Pearson developed the chi-square (χ2) test
– Determines whether the observed distribution of individuals in as predicted or occurs by chance.
– If there is no difference between the observed and expected classes
the value for χ2 will be 0.
– The value of χ2 increases with greater difference between the observed and expected classes.
– The formula can be expressed as χ2 = Σ (O-E)2 ÷ E
– O is # observed and E is # expected
We must now convert χ2 into probability in order to determine if the χ2 value is expected.
df (degrees of freedom) = number of classes – 1
We can then use the table below to determine whether the data collected is acceptable.
– A p value of less than 0.05 means that the observations do not meet the expected outcome and needs to be reexamined
9.8 Genetic traits in humans can be tracked through family pedigrees
The inheritance of human traits follows Mendel’s laws.
A pedigree
– shows the inheritance of a trait in a family through multiple generations,
– demonstrates dominant or recessive inheritance, and
– can also be used to deduce genotypes of family members.
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Figure 9.8ADominant Traits Recessive Traits
Freckles No freckles
Widow’s peak Straight hairline
Free earlobe Attached earlobe
Figure 9.8B
First generation(grandparents)
Second generation(parents, aunts,and uncles)
Third generation(two sisters)
Female MaleAttachedFree
Ff Ff Ffff
FfFfff ff ff
ff
FForFf
FForFf
9.9 Many inherited disorders in humans are controlled by a single gene
Inherited human disorders show either
1. recessive inheritance in which
– two recessive alleles are needed to show disease
– heterozygous parents are carriers of the disease-causing allele
– the probability of inheritance increases with inbreeding, mating between close relatives
2. dominant inheritance in which
– one dominant allele is needed to show disease and
– dominant lethal alleles are usually eliminated from the population.
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Figure 9.9A
Parents
Offspring
Sperm
Eggs
NormalDd
NormalDd
D
D
d
d
DDNormal
DdNormal(carrier)
DdNormal(carrier)
ddDeaf
9.9
The most common fatal genetic disease in the United States is cystic fibrosis (CF), resulting in excessive thick mucus secretions. The CF allele is
– recessive and
– carried by about 1 in 31 Americans.
Dominant human disorders include
– achondroplasia, resulting in dwarfism, and
– Huntington’s disease, a degenerative disorder of the nervous system.
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Table 9.9
New technologies offer ways to obtain genetic information
– before conception,
– during pregnancy, and
– after birth.
Genetic testing can identify potential parents who are heterozygous carriers for certain diseases.
9.10 New technologies can provide insight into one’s genetic legacy
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Several technologies can be used for detecting genetic conditions in a fetus.
– Amniocentesis extracts samples of amniotic fluid containing fetal cells
– Usually performed in the sixteenth week of pregnancy
– Chorionic villus sampling removes a sample of chorionic villus tissue from the placenta and permits similar karyotyping and biochemical tests.
– Usually performed in the eighth or ninth week of pregnancy
9.10 New technologies can provide insight into one’s genetic legacy
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Figure 9.10AAmniocentesis
Ultrasoundtransducer
Fetus
Placenta
UterusCervix
Amniotic fluidextracted
Centrifugation
Amniotic fluid
Fetal cells
Culturedcells
Several hours
Several weeks
Several weeks
Biochemicaland geneticstests
Several hours
Several hours
Fetal cells
Cervix
Uterus
Chorionicvilli
PlacentaFetus
Ultrasoundtransducer
Tissue extractedfrom the chorionic villi
Chorionic Villus Sampling (CVS)
Karyotyping
Blood tests on the mother at 14–20 weeks of pregnancy can help identify fetuses at risk for certain birth defects (neural tube defects and Down syndrome).
Fetal imaging enables a physician to examine a fetus directly for anatomical deformities. The most common procedure is ultrasound imaging, using sound waves to produce a picture of the fetus.
Newborn screening can detect diseases that can be prevented by special care and precautions.
PKU
9.10
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Figure 9.10B
New technologies raise ethical considerations that include
– the confidentiality and potential use of results of genetic testing,
– time and financial costs, and
– determining what, if anything, should be done as a result of the testing.
9.10
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9.12 Many genes have more than two alleles in the population
Although an individual can at most carry two different alleles for a particular gene, more than two alleles often exist in the wider population.
Human ABO blood group phenotypes involve three alleles for a single gene.
The four human blood groups, A, B, AB, and O, result from combinations of these three alleles.
The A and B alleles are both expressed in heterozygous individuals, a condition known as codominance.
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9.12 Many genes have more than two alleles in the population
In codominance,
– neither allele is dominant over the other and
– expression of both alleles is observed as a distinct phenotype in the heterozygous individual.
– AB blood type is an example of codominance.
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Figure 9.12
Blood Group(Phenotype) Genotypes
Carbohydrates Presenton Red Blood Cells
AntibodiesPresentin Blood
A
B
AB
O
IAIA
orIAi
IBIB
orIBi
IAIB
ii
Carbohydrate A
Carbohydrate B
Carbohydrate A
and
Carbohydrate B
Neither
Anti-B
Anti-A
Anti-B
Anti-A
None
No reaction Clumping reaction
O A B AB
Reaction When Blood from Groups Below Is Mixedwith Antibodies from Groups at Left
9.14 A single character may be influenced by many genes
Many characteristics result from polygenic inheritance, in which a single phenotypic character results from the additive effects of two or more genes.
Human skin color is an example of polygenic inheritance.
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Figure 9.14_1
P generation
F1 generation
aabbcc(very light)
AABBCC(very dark)
AaBbCc AaBbCc
Figure 9.14_2
F2 generation
Eggs
Sperm
81
81
81
81
81
81
81
81
81
81
81
81
81
81
81
81
641
646
6415
6420
641
646
6415
Figure 9.14_3
Skin color
Fra
ctio
n o
f p
op
ula
tio
n6420
6415
646
641
9.15 The environment affects many characters
Many characters result from a combination of heredity and the environment.
skin color is affected by exposure to sunlight
susceptibility to diseases, such as cancer, has hereditary and environmental components
identical twins show some differences
Complex traits are determined by the cumulative effects of genes and the influence of environment
Examples: Skin color and IQ
Only genetic influences are inherited.© 2012 Pearson Education, Inc.