09 Lecture Presentation PC

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2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

PowerPoint Lectures for

Campbell Biology: Concepts & Connections, Seventh EditionReece, Taylor, Simon, and Dickey

Chapter 9 Patterns of Inheritance


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Dogs are one of mans longest geneticexperiments.

Over thousands of years, humans have chosen and

mated dogs with specific traits.

The result has been an incredibly diverse array of dogs

with distinct

body types and

behavioral traits.

Introduction

2012 Pearson Education, Inc.


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Figure 9.0_1

Chapter 9: Big Ideas

Mendels Laws Variations on

Mendels Laws

The Chromosomal Basis

of Inheritance

Sex Chromosomes and

Sex-Linked Genes


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Figure 9.0_2


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MENDELS LAWS



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9.1 The science of genetics has ancient roots

Pangenesis, proposed around 400 BCE byHippocrates, was an early explanation for inheritancethat suggested that

particles called pangenes came from all parts of the

organism to be incorporated into eggs or sperm and

characteristics acquired during the parents lifetime couldbe transferred to the offspring.

Aristotle rejected pangenesis and argued that insteadof particles, thepotentialto produce the traits wasinherited.



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Figure 9.1


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9.1 The science of genetics has ancient roots

The idea that hereditary materials mix in formingoffspring, called the blending hypothesis, was

suggested in the 19th century by scientists studyingplants but

later rejected because it did not explain how traits thatdisappear in one generation can reappear in latergenerations.



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9.2 Experimental genetics began in an abbeygarden

Heredity is the transmission of traits from onegeneration to the next.

Genetics is the scientific study of heredity.

Gregor Mendel

began the field of genetics in the 1860s,

deduced the principles of genetics by breeding garden

peas, and

relied upon a background of mathematics, physics, and

chemistry.



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In 1866, Mendel correctly argued that parents pass on to their offspring

discrete heritable factors and

stressed that the heritable factors (today called genes),retain their individuality generation after generation.

A heritable feature that varies among individuals,such as flower color, is called a character.

Each variant for a character, such as purple or whiteflowers, is a trait.



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Figure 9.2A


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True-breeding varieties result when self-fertilizationproduces offspring all identical to the parent.

The offspring of two different varieties are hybrids.

The cross-fertilization is a hybridization, or geneticcross.

True-breeding parental plants are the P generation.

Hybrid offspring are the F1 generation.

A cross of F1 plants produces an F2 generation.


Fi 9 2B


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Figure 9.2B

Stamen

Carpel

Petal

Fi 9 2C 1


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Figure 9.2C_s1

Removal of

stamens

Carpel

White

Stamens

Transfer

of pollenPurpleParents

(P)

2

1

Figure 9 2C s2


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Figure 9.2C_s2

Removal of

stamens

Carpel

White

Stamens

Transfer

of pollenPurple

Carpel maturesinto pea pod

Parents

(P)

2

3

1

Figure 9 2C s3


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Figure 9.2C_s3

Removal of

stamens

Carpel

White

Stamens

Transfer

of pollenPurple

Carpel maturesinto pea pod

Seeds from

pod planted

Offspring

(F1)

Parents

(P)

2

3

1

4

Figure 9 2D


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Figure 9.2DCharacter Traits

Dominant Recessive

Flower color

Purple White

Flower position

Axial Terminal

Seed colorYellow Green

Seed shape

Round Wrinkled

Pod shape

Inflated Constricted

Pod colorGreen Yellow

Stem length

Tall Dwarf

Figure 9 2D 1


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Figure 9.2D_1

Character Traits

Dominant Recessive

Flower color

Purple White

Flower position

Axial Terminal

Seed color

Yellow Green

Seed shape

Round Wrinkled

Figure 9 2D 2


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Figure 9.2D_2

Character

Dominant Recessive

Traits

Pod shape

Inflated Constricted

Pod color

Green Yellow

Stem length

Tall Dwarf


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9.3 Mendels law of segregation describes theinheritance of a single character

A cross between two individuals differing in asingle character is a monohybrid cross.

Mendel performed a monohybrid cross between aplant with purple flowers and a plant with whiteflowers.

The F1 generation produced all plants with purpleflowers.

A cross of F1 plants with each other produced an F2generation with purple and white flowers.


Figure 9 3A s1


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Figure 9.3A_s1

The Experiment

P generation

(true-breeding

parents)

Purpleflowers

Whiteflowers

Figure 9 3A s2


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Figure 9.3A_s2

The Experiment

P generation

(true-breeding

parents)

F1 generation

Purpleflowers

Whiteflowers

All plants have

purple flowers


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9 3 M d l l f i d ib h


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The all-purple F1 generation did not produce lightpurple flowers, as predicted by the blendinghypothesis.

Mendel needed to explain why

white color seemed to disappear in the F1 generationand

white color reappeared in one quarter of the F2offspring.

Mendel observed the same patterns of inheritancefor six other pea plant characters.


9 3 M d l l f i d ib h


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Mendel developed four hypotheses, describedbelow using modern terminology.

1. Alleles are alternative versions of genes that account

for variations in inherited characters.

2. For each characteristic, an organism inherits two

alleles, one from each parent. The alleles can be the

same or different.

A homozygous genotype has identical alleles.

A heterozygous genotype has two different alleles.


9 3 M d l l f ti d ib th


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3. If the alleles of an inherited pair differ, then onedetermines the organisms appearance and is called the

dominant allele. The other has no noticeable effect on

the organisms appearance and is called the recessive

allele.

The phenotype is the appearance or expression of a trait.

The genotype is the genetic makeup of a trait.

The same phenotype may be determined by more than one

genotype.


9 3 M d l l f ti d ib th


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4. A sperm or egg carries only one allele for each inheritedcharacter because allele pairs separate (segregate) from

each other during the production of gametes. This

statement is called the law of segregation.

Mendels hypotheses also explain the 3:1 ratio in theF2 generation.

The F1 hybrids all have a Pp genotype.

A Punnett square shows the four possible combinations

of alleles that could occur when these gametes combine.


Figure 9.3B_s1


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The Explanation

P generation Genetic makeup (alleles)

Purple flowers White flowers

Gametes All p

ppPP

PAll

Figure 9.3B_s2


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The Explanation

P generation

F1 generation

(hybrids)

Genetic makeup (alleles)


Gametes All p

ppPP

P pGametes

All Pp

2

1

2

1

PAll

Figure 9.3B_s3


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The Explanation

P generation

F1 generation

(hybrids)

F2 generation

Genetic makeup (alleles)


Gametes P All p

ppPP

P

P

P

p

p

p

PP Pp

Pp pp

Eggs

from F1

plant

Gametes

Fertilization

All Pp

Alleles

segregate

Phenotypic ratio

3 purple : 1 white

Genotypic ratio

1 PP: 2 Pp: 1 pp

Sperm from F1 plant

2

1

2

1

All

Figure 9.3B_4


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F2 generation

P

P

p

p

PP Pp

Pp pp

Eggs

from F1

plant

Phenotypic ratio

3 purple : 1 white

Genotypic ratio

1 PP : 2 Pp : 1 pp

Sperm from F1 plant

9 4 H l h b th ll l


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9.4 Homologous chromosomes bear the allelesfor each character

A locus (plural, loci) is the specific location of agene along a chromosome.

For a pair of homologous chromosomes, alleles ofa gene reside at the same locus.

Homozygous individuals have the same allele on bothhomologues.

Heterozygous individuals have a different allele on

each homologue.


Figure 9.4


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P

P

a

a

B

b

PP aa Bb

Dominant

allele

Recessive

allele

Gene loci

Homologous

chromosomes

Genotype:

Heterozygous,

with one dominant

and one recessive

allele

Homozygous

for the

recessive

allele

Homozygous

for the

dominant

allele

9 5 The law of independent assortment is


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9.5 The law of independent assortment isrevealed by tracking two characters at once

A dihybrid cross is a mating of parental varietiesthat differ in two characters.

Mendel performed the following dihybrid cross withthe following results:

P generation: round yellow seeds wrinkled green seeds

F1 generation: all plants with round yellow seeds

F2 generation:

9/16 had round yellow seeds 3/16 had wrinkled yellow seeds

3/16 had round green seeds

1/16 had wrinkled green seeds


Figure 9.5A


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41

41

41

41

41

41

41

4

1

169

163

163

161

2

1

2

1

21

21

F1 generation

F2 generation

P generation

Gametes

Sperm

Eggs

Yellowround

Greenround

Yellowwrinkled

Greenwrinkled

RRYY rryy

RY ry

RrYy

The hypothesis of dependent assortment

Data did not support; hypothesis refutedThe hypothesis of independent assortment

Actual results; hypothesis supported

RY

RY

ry

ry

Eggs

RY

RY

rY

rY

Ry

Ry ry

ry

RRYY RrYY RRYy RrYy

RrYY rrYY RrYy rrYy

RRYy RrYy RRyy Rryy

RrYy rrYy Rryy rryy

Sperm

Figure 9.5A_1


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F1 generation

P generation

Gametes

RRYY rryy

RY ry

RrYy

Figure 9.5A_2


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21

F2 generation

The hypothesis of dependent assortment

Data did not support; hypothesis refuted

RY

RY

ry

ry

Eggs

Sperm

21

21

21

F1 generation RrYy


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Mendel needed to explain why the F2 offspring had new nonparental combinations of traits and

a 9:3:3:1 phenotypic ratio.

Mendel

suggested that the inheritance of one character has noeffect on the inheritance of another,

suggested that the dihybrid cross is the equivalent to twomonohybrid crosses, and

called this the law of independent assortment.




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The following figure demonstrates the law ofindependent 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 9.6


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What is the genotype of the black dog?

Two possibilities for the black dog:

Testcross

Genotypes

Gametes

Offspring All black 1 black : 1 chocolate

or

B_? bb

BbBB

B B

b b

b

Bb Bb bb

9 7 Mendels laws reflect the rules of probability


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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 notto occur has a probability of 0.



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9.8 CONNECTION: Genetic traits in humans can


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9.8 CONNECTION: Genetic traits in humans canbe tracked through family pedigrees

In a simple dominant-recessive inheritance ofdominant alleleA and recessive allele a,

a recessive phenotype always results from a

homozygous recessive genotype (aa) but

a dominant phenotype can result from either

the homozygous dominant genotype (AA) or

a heterozygous genotype (Aa).

Wild-type traits, those prevailing in nature, are

not necessarily specified by dominant alleles.


Figure 9.8ADominant Traits Recessive Traits


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Freckles No freckles

Widows peak Straight hairline

Free earlobe Attached earlobe

Figure 9.8A_1


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Freckles

Figure 9.8A_2


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No freckles


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Figure 9.8A_4


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Straight hairline


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9.8 CONNECTION: Genetic traits in humans can


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be tracked through family pedigrees

The inheritance of human traits follows Mendelslaws.

A pedigree

shows the inheritance of a trait in a family throughmultiple generations,

demonstrates dominant or recessive inheritance, and

can also be used to deduce genotypes of familymembers.



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9.9 CONNECTION: Many inherited disorders in


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yhumans are controlled by a single gene

Inherited human disorders show either1. recessive inheritance in which

two recessive alleles are needed to show disease,

heterozygous parents are carriers of the disease-causingallele, and

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.


Figure 9.9A

ParentsNormal Normal


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Parents

Offspring

Sperm

Eggs

Dd Dd

D

D

d

d

DD

Normal

DdNormal

(carrier)

Dd

Normal

(carrier)

dd

Deaf


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Table 9.9


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Figure 9.9B


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9.10 CONNECTION: New technologies can


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New technologies offer ways to obtain geneticinformation

before conception,

during pregnancy, and

after birth.

Genetic testing can identify potential parents who

are heterozygous carriers for certain diseases.

gprovide insight into ones genetic legacy




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Several technologies can be used for detectinggenetic conditions in a fetus.

Amniocentesis extracts samples of amniotic fluid

containing fetal cells and permits

karyotyping and

biochemical tests on cultured fetal cells to detect other

conditions, such as Tay-Sachs disease.

Chorionic villus sampling removes a sample of

chorionic villus tissue from the placenta and permitssimilar karyotyping and biochemical tests.

provide insight into ones genetic legacy



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Video: Ultrasound of Human FetusUse windows controls to play

Figure 9.10A Amniocentesis

Amniotic fluid Tissue extracted

Chorionic Villus Sampling (CVS)


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Ultrasound

transducer

Fetus

Placenta

Uterus

Cervix

Amniotic fluid

extracted

Centrifugation

Amniotic fluidFetal cells

Cultured

cells

Several

hours

Several

weeks

Several

weeks

Biochemical

and genetics

tests

Several

hours

Several

hours

Fetal cells

Cervix

Uterus

Chorionic

villi

Placenta

Fetus

Ultrasound

transducer

Tissue extracted

from the

chorionic villi

Karyotyping



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Blood tests on the mother at 1420 weeks ofpregnancy can help identify fetuses at risk for

certain birth defects.

Fetal imaging enables a physician to examine a

fetus directly for anatomical deformities. The mostcommon procedure is ultrasound imaging, using

sound waves to produce a picture of the fetus.

Newborn screening can detect diseases that canbe prevented by special care and precautions.




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Figure 9.10B_1


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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.




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VARIATIONS ONMENDELS LAWS


9.11 Incomplete dominance results ini i


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intermediate phenotypes

Mendels pea crosses always looked like one of the

parental varieties, called complete dominance.

For some characters, the appearance of F1 hybrids

falls between the phenotypes of the two parental

varieties. This is called incomplete dominance, in

which

neither allele is dominant over the other and

expression of both alleles occurs.


Figure 9.11AP generation


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F1 generation

F2 generation

21

21

2

1

2

1

21

21

Gametes

Gametes

Eggs

Sperm

Red

RR

White

r r

Pink hybrid

Rr

R

R

R

R

r

r

r

r

RR rR

Rr rr


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Figure 9.11A_3


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2

12

1

2

1

2

1

F2 generation

Eggs

Sperm

R

R

r

r

RR rR

Rr rr

9.11 Incomplete dominance results ini t di t h t


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intermediate phenotypes

Incomplete dominance does not support the

blending hypothesis because the original parental

phenotypes reappear in the F2 generation.

One example of incomplete dominance in humans

is hypercholesterolemia, in which

dangerously high levels of cholesterol occur in the blood

and

heterozygotes have intermediately high cholesterol

levels.


Figure 9.11B


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Normal Mild disease Severe disease

Phenotypes

Cell

LDL

receptor

LDL

HH

Homozygous

for ability to make

LDL receptors

hh

Homozygous

for inability to make

LDL receptors

Genotypes

Hh

Heterozygous

9.12 Many genes have more than two alleles inth l ti


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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. 2012 Pearson Education, Inc.


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Figure 9.12


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BloodGroup

(Phenotype) Genotypes

Carbohydrates Present

on Red Blood Cells

AntibodiesPresent

in Blood

A

B

AB

O

IA IA

or

IA i

IBIB

or

IBi

IA IB

i i

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 Mixed

with Antibodies from Groups at Left

Figure 9.12_1

Blood

Group Carbohydrates Present


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Group

(Phenotype) Genotypes

Carbohydrates Present

on Red Blood Cells

A

B

AB

O

I

A

I

A

or

IA i

IBIB

orIBi

IA IB

ii

Carbohydrate A

Carbohydrate B

Carbohydrate A

and

Carbohydrate B

Neither

Figure 9.12_2


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Antibodies

Present

in Blood

Anti-B

Anti-A

Anti-B

Anti-A

None

O A B AB

Reaction When Blood from Groups Below Is

Mixed with Antibodies from Groups at Left

Blood

Group

(Phenotype)

A

B

AB

O

9.13 A single gene may affect many phenotypiccharacters


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characters

Pleiotropy occurs when one gene influences many

characteristics.

Sickle-cell disease is a human example of pleiotropy.

This disease

affects the type of hemoglobin produced and the shape of

red blood cells and

causes anemia and organ damage.

Sickle-cell and nonsickle alleles are codominant.

Carriers of sickle-cell disease are resistant to malaria.


Figure 9.13A


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Figure 9.13B An individual homozygous for the sickle-cell allele


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Produces sickle-cell (abnormal) hemoglobin

The abnormal hemoglobin crystallizes,causing red blood cells to become sickle-shaped

Sickled cell

The multiple effects of sickled cells

Damage to organs Other effects

Kidney failure

Heart failure

Spleen damage

Brain damage (impaired

mental function,

paralysis)

Pain and fever

Joint problems

Physical weakness

Anemia

Pneumonia and other

infections

9.14 A single character may be influenced bymany genes


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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.


Figure 9.14P generation

aabbcc

( li ht)AABBCC

( d k)


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F1 generation

F2 generation

Eggs

Sperm

Skin color

Fractiono

fpopulation

(very light) (very dark)

AaBbCc AaBbCc

81

64

15

64

20

64

6

64

1

64

15

64

6

64

1

81

81

8

1

81

81

81

81

81

81

81

81

81

81

81

81

Figure 9.14_1


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P generation

F1 generation

aabbcc

(very light)AABBCC

(very dark)

AaBbCc AaBbCc

Figure 9.14_2 Sperm

81

81

81

81

81

81

81

81


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F2 generation

Eggs

81

81

81

81

81

81

81

81

8 8 8 8 8 8 8 8

64

1

64

6

64

15

64

20

64

1

64

6

64

15


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9.15 The environment affects many characters


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Many characters result from a combination of

heredity and the environment. For example,

skin color is affected by exposure to sunlight,

susceptibility to diseases, such as cancer, has

hereditary and environmental components, and

identical twins show some differences.

Only genetic influences are inherited.


Figure 9.15A


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Figure 9.15B


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9.16 Chromosome behavior accounts forMendels laws


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Mendel s laws

The chromosome theory of inheritance states that

genes occupy specific loci (positions) on chromosomes

and

chromosomes undergo segregation and independent

assortment during meiosis.


9.16 Chromosome behavior accounts forMendels laws


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Mendel s laws

Mendels laws correlate with chromosomeseparation in meiosis.

The law of segregation depends on separation ofhomologous chromosomes in anaphase I.

The law of independent assortment depends onalternative orientations of chromosomes in metaphase I.


Figure 9.16_s1F1 generation All yellow round seeds

(RrYy)rR

y


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Meta-phase I

of meiosis

Y y

R r r R

Y

Y y


(RrYy)rR

y


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Meta-phase I

of meiosis

Anaphase I

Metaphase IIR

y

r

YY

R r

y

Y

Y

y

y

R

R

r

r r

r

R

R

Y

Y

Y

y

y


(RrYy)rR

y


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4

1

4

1

4

1

4

1

Meta-phase I

of meiosis

Anaphase I

Metaphase II

Fertilization

Gametes

F2 generation 9 :3 :3 :1

RY ry rY Ry

R

R

R

yy

y

rr

r

YY

Y

YY

Y

R

R R

r

rr

y

yy

Y

Y

y

y

R

R

r

r r

r

R

R

Y

Y

Y

y

y

Figure 9.16_4


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Sperm

Eggs

Yellow

round

Green

round

Yellow

wrinkled

Green

wrinkled

RY

RY

rY

rY

Ry

Ry ry

ry

RRYYRrYYRRYy RrYy

RrYY rrYY RrYy rrYy

RRYy RrYy RRyy Rryy

RrYy rrYy Rryy rryy

41

169

163

163

161

41

41

41

41

41

41

41

9.17 SCIENTIFIC DISCOVERY: Genes on the samechromosome tend to be inherited together


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c o oso e te d to be e ted toget e

Bateson and Punnett studied plants that did not show

a 9:3:3:1 ratio in the F2 generation. What they found

was an example oflinked genes, which

are located close together on the same chromosome and

tend to be inherited together.


Figure 9.17 The Experiment

Purple flower


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Long pollenPpLl PpLl

Phenotypes Observed

offspring

Prediction

(9:3:3:1)

Purple longPurple round

Red long

Red round

28421

21

55

21571

71

24

The Explanation: Linked Genes

Parental

diploid cell

PpLl

Meiosis

P L

P L

p l

p lMost

gametes

Fertilization

Sperm

Most

offspring Eggs

3 purple long : 1 red round

Not accounted for: purple round and red long

P L P L

P L

P L

PL

PL

p l

p l

p l

p l

p l

p l

Figure 9.17_1


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The Experiment

Purple flower

Long pollenPpLl PpLl

Phenotypes Observed

offspring

Prediction

(9:3:3:1)

Purple long

Purple roundRed long

Red round

284

2121

55

215

71

7124

Figure 9.17_2 The Explanation: Linked Genes

Parental P L


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diploid cell

PpLl

Meiosis

P L

p l

p lMost

gametes

Fertilization

Sperm

Mostoffspring Eggs

3 purple long : 1 red round

Not accounted for: purple round and red long

P L P L

P L

P L

PL

PL

p l

p l

p l

p l

p l

pl

9.18 SCIENTIFIC DISCOVERY: Crossing overproduces new combinations of alleles


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p

Crossing over between homologous

chromosomes produces new combinations of

alleles in gametes.

Linked alleles can be separated by crossing over,

forming recombinant gametes.

The percentage of recombinants is the

recombination frequency.


Figure 9.18A


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P L

Tetrad

(pair of

homologous

chromosomes)

p l

p lp L

p L P lCrossing over

Parental gametes

Recombinant gametes

Figure 9.18B


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Figure 9.18C


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The Experiment

Female Male

ggl lGgLl

Black body,

vestigial wings

Gray body,

long wings

(wild type)

Offspring

Gray long Black vestigial Gray vestigial Black long

Recombinantphenotypes

Parentalphenotypes

Recombination frequency 0.17 or 17%391 recombinants2,300 total offspring

965 944 206 185

Offspring

Parental Recombinant

Eggs Sperm

Crossing over

G L

g l g l

g l

g l g l

G l gL

G L g l G l gL g l

g l g l

g l

The Explanation

GgLl

Femaleggl l

Male

G L

Figure 9.18C_1

The Experiment

Black bodyGray body


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Female Male

ggl lGgLl

Black body,

vestigial wings

Gray body,

long wings

(wild type)

Offspring: Gray long Black vestigial Gray vestigial Black long

Recombinant

phenotypes

Parental

phenotypes

Recombination frequency 0.17 or 17%391 recombinants2,300 total offspring

965 944 206 185

Figure 9.18C_2

The Explanation


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Offspring

Parental Recombinant

Eggs Sperm

Crossing over

G Lg l g l

g l

g l g lG l

g L

G L g l G l g L g l

g l g l

g lGgLl

Femaleggl l

Male

G L

9.19 Geneticists use crossover data to map genes


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When examining recombinant frequency, Morgan

and his students found that the greater the

distance between two genes on a chromosome,

the more points there are between them where

crossing over can occur. Recombination frequencies can thus be used to

map the relative position of genes on

chromosomes.


Figure 9.19A


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Section of chromosome carrying linked genes

Recombination

frequencies

17%

9% 9.5%

g c l

Figure 9.19B


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Mutant phenotypes

Short

aristae

Black

body(g)

Cinnabar

eyes(c)

Vestigial

wings(l)

Brown

eyes

Red

eyes

Normal

wings(L )

Red

eyes(C)

Gray

body(G)

Long aristae

(appendageson head)

Wild-type phenotypes


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SEX CHROMOSOMES ANDSEX-LINKED GENES



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Figure 9.20A


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X

Y

Figure 9.20B


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Parents(diploid)

Gametes

(haploid)

Offspring

(diploid)

Female

Female

Male

Male

EggSperm

44

XY

44

XX

22X

22

Y

22X

44

XX

44

XY


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9.20 Chromosomes determine sex in manyspecies


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Grasshoppers, roaches, and some other insects

have an X-O system, in which

O stands for the absence of a sex chromosome,

females are XX, and

males are XO.

In certain fishes, butterflies, and birds,

the sex chromosomes are Z and W, males are ZZ, and

females are ZW.


Figure 9.20C


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22

XX

22X

Male Female


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Figure 9.20D


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76

ZW

76

ZZ

Male Female


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Some organisms lack sex chromosomes altogether.

In bees, sex is determined by chromosome number.

Females are diploid.

Males are haploid.


Figure 9.20E


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Male Female

16 32

Figure 9.20E_1


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In some animals, environmental temperature

determines the sex.

For some species of reptiles, the temperature at which

the eggs are incubated during a specific period of

development determines whether the embryo will developinto a male or female.

Global climate change may therefore impact the sex ratio

of such species.



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Figure 9.21A


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Figure 9.21A_1


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Figure 9.21B

MaleFemale

XrYXRXR


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Sperm

Eggs

R red-eye alleler white-eye allele

XR

Xr

XrYXRXR

XRXr XRY

Y

Figure 9.21C

MaleFemale

XRYXRXr


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R red-eye alleler white-eye allele

Sperm

Eggs

XR

xR

Y

Xr XrY

XRYXRXR

XrXR


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9.22 CONNECTION: Human sex-linkeddisorders affect mostly males


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Most sex-linked human disorders are

due to recessive alleles and

seen mostly in males.

A male receiving a single X-linked recessive allelefrom his mother will have the disorder.

A female must receive the allele from both parents

to be affected.



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Figure 9.22


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Female Male

Hemophilia

Carrier

NormalAlexis

Alexandra Czar

Nicholas II

of Russia

Queen

Victoria

Alice Louis

Albert

Figure 9.22_1


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9.23 EVOLUTION CONNECTION: The Ychromosome provides clues about humanmale evolution


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male evolution

The Y chromosome provides clues about humanmale evolution because

Y chromosomes are passed intact from father to son

and

mutations in Y chromosomes can reveal data about

recent shared ancestry.


Figure 9.23


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You should now be able to


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1. Describe pangenesis theory and the blending

hypothesis. Explain why both ideas are nowrejected.

2. Define and distinguish between true-breeding

organisms, hybrids, the P generation, the F1generation, and the F2 generation.

3. Define and distinguish between the following pairs of

terms: homozygous and heterozygous; dominantallele and recessive allele; genotype and phenotype.

Also, define a monohybrid cross and a Punnett

square. 2012 Pearson Education, Inc.



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4. Explain how Mendels law of segregation

describes the inheritance of a singlecharacteristic.

5. Describe the genetic relationships between

homologous chromosomes.

6. Explain how Mendels law of independent

assortment applies to a dihybrid cross.

7. Explain how and when the rule of multiplication

and the rule of addition can be used to determine

the probability of an event.




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8. Explain how family pedigrees can help

determine the inheritance of many human traits.

9. Explain how recessive and dominant disorders

are inherited. Provide examples of each.

10. Compare the health risks, advantages, and

disadvantages of the following forms of fetal

testing: amniocentesis, chorionic villus sampling,

and ultrasound imaging.



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15. Explain how linked genes are inherited differently

from nonlinked genes.

16. Describe T. H. Morgans studies of crossing over in

fruit flies. Explain how Sturtevant created linkage

maps.17. Explain how sex is genetically determined in humans

and the significance of the SRYgene.

18. Describe patterns of sex-linked inheritance and

examples of sex-linked disorders.

19. Explain how the Y chromosome can be used to trace

human ancestry.


Figure 9.UN01


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Fertilization

Meiosis

Homologouschromosomes

Alleles, residingat the same locus

Paired alleles,different formsof a gene Haploid gametes

(allele pairs separated)

Gamete

from theotherparent

Diploid zygote

(containingpaired alleles)


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Figure 9.UN03


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Single

gene

PleiotropyMultiple characters

Figure 9.UN04


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Multiple

genes

Polygenic

inheritance

Single characters(such as skin color)

Figure 9.UN05

Genes

l t d lt ti


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chromosomes

heterozygous

located

onalternative

versions called

at specific

locations calledif both are the same,

the genotype is calledif different, the

genotype is called

the expressed

allele is calledthe unexpressed

allele is called

inheritance when the phenotypeis in between is called

(a)

(b) (c)

(d) (e)

(f)

Figure 9.UN06


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