© 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.