BIOLOGY Outline Chapter 11: 10th Edition Mendelian ...

Sylvia S. Mader

Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or displayPowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor

BIOLOGY10th Edition

Mendelian Patterns of Inheritance

Chapter 11: pp. 189 - 210

1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Parents

eggs

Ee Ee

spem

Punn

ett s

quar

e

Offspring

E e

E

e

Ee

EeEE

ee

TT tt

tT

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eggs

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Offspring

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Outline

!Blending Inheritance!Monohybrid Cross

!Law of Segregation!Modern Genetics

!Genotype vs. Phenotype!Punnett Square

!Dihybrid Cross!Law of Independent Assortment

!Human Genetic Disorders

3

Gregor Mendel

!Austrian monk!Studied science and mathematics at University of Vienna!Conducted breeding experiments with the garden pea

Pisum sativum!Carefully gathered and documented mathematical data

from his experiments!Formulated fundamental laws of heredity in early

1860s!Had no knowledge of cells or chromosomes!Did not have a microscope

4

Gregor MendelCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© Ned M. Seidler/Nationa1 Geographic Image Collection

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Fruit and Flower of the Garden Pea


a.

Flower Structure

filamentanther

stamen

stigmastyle

ovules inovary

carpel

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Garden Pea Traits Studied by Mendel


Cutting awayanthers

Brushing onpollen fromanother plant

All peas are yellow whenone parent produces yellowseeds and the other parentproduces green seeds.

7

Blending Inheritance

!Theories of inheritance in Mendel’s time:!Based on blending!Parents of contrasting appearance produce

offspring of intermediate appearance!Mendel’s findings were in contrast with this

!He formulated the particulate theory of inheritance!Inheritance involves reshuffling of genes from

generation to generation

8

One-Trait Inheritance

!Mendel performed cross-breeding experiments!Used “true-breeding” (homozygous) plants!Chose varieties that differed in only one trait

(monohybrid cross)!Performed reciprocal crosses

!Parental generation = P!First filial generation offspring = F1 !Second filial generation offspring = F2

!Formulated the Law of Segregation

9

Mendel’s Monohybrid Crosses:An Example


TT tt

tT

P generation

P gametes

F1 gametes

F2 generation

F1 generation

Tt

T t

sper

m

T

t

TT Tt

Tt tt

Offspring

Phenotypic Ratio

short1tall3

Allele KeyT = tall plantt = short plant

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Law of Segregation

!Each individual has a pair of factors (alleles) for each trait

!The factors (alleles) segregate (separate) during gamete (sperm & egg) formation

!Each gamete contains only one factor (allele) from each pair

!Fertilization gives the offspring two factors for each trait

11

Modern Genetics View

!Each trait in a pea plant is controlled by two alleles (alternate forms of a gene)

!Dominant allele (capital letter) masks the expression of the recessive allele (lower-case)

!Alleles occur on a homologous pair of chromosomes at a particular gene locus!Homozygous = identical alleles

!Heterozygous = different alleles

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Homologous Chromosomes

Replication

alleles at agene locus

sister chromatids

b. Sister chromatids of duplicated chromosomes have same alleles for each gene.

a. Homologous chromosomes have alleles for same genes at specific loci.

G

R

S

t

G

R

S

t

G

R

S

t

g

r

s

T

g

r

s

T

g

r

s

T


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Genotype versus Phenotype

!Genotype

!Refers to the two alleles an individual has for a specific trait

! If identical, genotype is homozygous

! If different, genotype is heterozygous

!Phenotype

!Refers to the physical appearance of the individual

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Genotype versus Phenotype

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Punnett Square

!Table listing all possible genotypes resulting from a cross

!All possible sperm genotypes are lined up on one side

!All possible egg genotypes are lined up on the other side

!Every possible zygote genotypes are placed within the squares

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Punnett Square

!Allows us to easily calculate probability, of genotypes and phenotypes among the offspring

!Punnett square in next slide shows a 50% (or !) chance !The chance of E = !!The chance of e = !

!An offspring will inherit:!The chance of EE =!!!=" !The chance of Ee =!!!=" !The chance of eE =!!!=" !The chance of ee =!!!="

17

Punnett Square Showing Earlobe Inheritance Patterns

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Parents

Ee Ee

eggs

spem

Punn

ett s

quar

e

Offspring

E e

E

e

Ee

EeEE

e e

Allele key Phenotypic Ratio

unattached earlobes3

1

E = unattached earlobese = attached earlobes attached earlobes

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Monohybrid Test cross

! Individuals with recessive phenotype always have the homozygous recessive genotype

!However, individuals with dominant phenotype have indeterminate genotype

!May be homozygous dominant, or

!Heterozygous

!Test cross determines genotype of individual having dominant phenotype

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One-Trait Test Cross

Insert figure 11.7a here

Phenotypic Ratio

eggs

a.

sper

m

t

T

t

Offspring

Tt tt

Tt

tt

Allele Key

short1tall1

T = tall plantt = short plant


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One-Trait Test Cross


b.

tT

Tt

Offspring

eggssperm

TT tt

Allele Key

Phenotypic RatioAll tall plants

T = tall plantt = short plant

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Two-Trait Inheritance

! Dihybrid cross uses true-breeding plants differing in two traits

! Observed phenotypes among F2 plants

! Formulated Law of Independent Assortment

! The pair of factors for one trait segregate independently of the factors for other traits

! All possible combinations of factors can occur in the gametes! Mendel tracked each trait through two generations.

! P generation is the parental generation in a breeding experiment.! F1 generation is the first-generation offspring in a breeding

experiment.! F2 generation is the second-generation offspring in a breeding

experiment

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Two-Trait (Dihybrid) Cross


TtGg

ttgg

TTGG

Offspring

P generation

P gametes

F2 generation

F1 generation

F1 gametes

eggs

sper

m

TG Tg

TG

Tg

tg

tG

tG tg

tgTG

TTGg TtGG TtGg

TTGg Ttgg

TtGG ttGG ttGg

TtGg Ttgg ttGg

ttggTTGG

TtGg

TTgg

TtGg

Allele Key====

TtGg

tall plantshort plantgreen podyellow pod

Phenotypic Ratio9 tall plant, green pod3 tall plant, yellow pod3 short plant, green pod1 short plant, yellow pod

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Independent Assortment and Segregation during Meiosis


Parent cell has twopairs of homologouschromosomes.

All possible combina-tions of chromosomesand alleles occur inthe gametes assuggested by Mendel'stwo laws.

All orientations of ho-mologous chromosomesare possible at meta-phase I in keeping withthe law of independentassortment.

At metaphase II, eachdaughter cell has onlyone member of eachhomologous pair inkeeping with the law ofsegregation.

A

A A

A A

A

A

AB

ab

Ab

aB

a

a

a

a

aa

a

A

AbA

aa aB

B

BB

B

B

B

B

B

Ba

B

b

b b

A A

b b BB

a a

b

b

b

b

b

A

b

b

either

or

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Human Genetic Disorders

! Genetic disorders are medical conditions caused by alleles inherited from parents

! Autosome - Any chromosome other than a sex chromosome (X or Y)

! Genetic disorders caused by genes on autosomes are called autosomal disorders ! Some genetic disorders are autosomal dominant

! An individual with AA has the disorder! An individual with Aa has the disorder! An individual with aa does NOT have disorder

! Other genetic disorders are autosomal recessive! An individual with AA does NOT have disorder! An individual with Aa does NOT have disorder, but is a carrier! An individual with aa DOES have the disorder

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Autosomal Recessive Pedigree ChartCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Autosomal recessive disorders• Most affected children have unaffected parents.• Heterozygotes (Aa) have an unaffected phenotype.• Two affected parents will always have affected children.• Close relatives who reproduce are more likely to have affected children.• Both males and females are affected with equal frequency.

aa aa

Aa Aa

Aa

A? A?

A?

Aa

*

aa A?

A?A?

Key

aa = affectedAa = carrier (unaffected)AA = unaffectedA? = unaffected(one allele unknown)

I

II

III

IV

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Autosomal Dominant Pedigree Chart

Aa

aa aa aa

aaaaaaaaAa

aa

Aa

Aa A?

Aa

Autosomal dominant disorders• affected children will usually have an affected parent.• Heterozygotes (Aa) are affected. Two affected parents can produce an unaffected child.• Two unaffected parents will not have affected children.• Both males and females are affected with equal frequency.

*

I

II

III

•

KeyAA = affectedAa = affected

A? = affected(one allele unknown)aa = unaffected


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Autosomal Recessive Disorders

!Tay-Sachs Disease!Progressive deterioration of psychomotor functions

!Cystic Fibrosis!Mucus in bronchial tubes and pancreatic ducts is

particularly thick and viscous

!Phenylketonuria (PKU)!Lack enzyme for normal metabolism of phenylalanine

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Cystic Fibrosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cl-H2O

H2O

H2O

Cl-Cl-

Cl-Cl-

thick mucus

defectivechannel

nebulizer

percussionvest

© Pat Pendarvis

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MethemoglobinemiaCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Courtesy Division of Medical Toxicology, University of Virginia

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Autosomal Dominant Disorders

!Neurofibromatosis!Tan or dark spots develop on skin and darken !Small, benign tumors may arise from fibrous nerve

coverings!Huntington Disease

!Neurological disorder!Progressive degeneration of brain cells

!Severe muscle spasms!Personality disorders

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A Victim of Huntington Disease


a: © Steve Uzzell

JJ JK JK JK

JK JJ

KL JK JK JK JK KL JK JK KL KK KL JL JJ

JL JK

JL KL KL

JL JL JL JL JJ KL JJ KL JJ KL KL

a. b.

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Incomplete Dominance

!Heterozygote has phenotype intermediate between that of either homozygote

!Homozygous red has red phenotype

!Homozygous white has white phenotype

!Heterozygote has pink (intermediate) phenotype

!Phenotype reveals genotype without test cross

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Incomplete DominanceCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

R1 R2

R1

R2

R1R2

R1R2R1R1

R2R2

R1R2 R1R2

eggs

sper

m

Offspring

Key1 R1R12 R1R21 R2R2

redpinkwhite

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Multiple Allelic Traits

! Some traits controlled by multiple alleles

! The gene exists in several allelic forms (but each individual only has two)

! ABO blood types

! The alleles:! IA = A antigen on red cells, anti-B antibody in plasma

! IB = B antigen on red cells, anti-AB antibody in plasma

! I = Neither A nor B antigens, both antibodies

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Multiple Allelic Traits

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Pleioptropic Effects!Pleiotropy occurs when a single mutant

gene affects two or more distinct and seemingly unrelated traits. !Marfan syndrome have disproportionately long

arms, legs, hands, and feet; a weakened aorta; poor eyesight

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Marfan Syndrome


(Left): © AP/Wide World Photos; (Right): © Ed Reschke

Chest wall deformitiesLong, thin fingers, arms, legsScoliosis (curvature of the spine)Flat feetLong, narrow faceLoose joints

Skeleton SkinLungsEyes

Mitral valveprolapse

Lens dislocationSevere nearsightedness Collapsed lungs

Stretch marks in skinRecurrent herniasDural ectasia: stretching of the membrane that holds spinal fluid

Enlargementof aorta

Heart and blood vessels

AneurysmAortic wall tear

Connectivetissue defects

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Polygenic Inheritance

!Occurs when a trait is governed by two or more genes having different alleles

!Each dominant allele has a quantitative effect on the phenotype

!These effects are additive

!Result in continuous variation of phenotypes

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Frequency Distributions in Polygenic Inheritance


F2 generation

F1 generation

P generation

aabbcc

Aabbcc

AaBbcc

AaBbCc

AABbCc

AABBCc

AABBCC

Genotype Examples

1

64—

6—64

15—64

20—64

Prop

ortio

n of

Pop

ulat

ion

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X – Linked Inheritance

! In mammals!The X and Y chromosomes determine gender!Females are XX !Males are XY

!The term X-linked is used for genes that have nothing to do with gender!Carried on the X chromosome. !The Y chromosome does not carry these genes !Discovered in the early 1900s by a group at Columbia

University, headed by Thomas Hunt Morgan. ! Performed experiments with fruit flies

! They can be easily and inexpensively raised in simple laboratory glassware

! Fruit flies have the same sex chromosome pattern as humans

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X – Linked InheritanceCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Offspring

eggs

sper

m

P generation

P gametes

F2 generation

F1 generation

F1 gametes

XRXRXrY

Xr XRY

XRY XRXr

XrXR

XRXrXRXR

XrYXRY

XR

Y

Allele Key

XR = red eyesXr = white eyes

Phenotypic Ratio

females: all red-eyedmales : 1 red-eyed 1 white-eyed

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Human X-Linked Disorders! Several X-linked recessive disorders occur in humans:

! Color blindness! The allele for the blue-sensitive protein is autosomal! The alleles for the red- and green-sensitive pigments are on the X chromosome.

! Menkes syndrome! Caused by a defective allele on the X chromosome ! Disrupts movement of the metal copper in and out of cells.

! Muscular dystrophy! Wasting away of the muscle

! Adrenoleukodystrophy! X-linked recessive disorder! Failure of a carrier protein to move either an enzyme or very long chain fatty acid into

peroxisomes. ! Hemophilia

! Absence or minimal presence of a clotting factor VIII, or clotting factor IX ! Affected person’s blood either does not clot or clots very slowly.

X-Linked Recessive Pedigree

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XBXB XbY grandfather

daughterXBXbXBY XBY XbXb

XbY

XBXb grandsonXBY XBXB XbY

KeyXBXB = Unaffected femaleXBXb = Carrier femaleXbXb = Color-blind femaleXbY = Unaffected maleXbY = Color-blind maleX-Linked Recessive

Disorders• More males than females are affected.

• An affected son can have parents who have the normal phenotype.• For a female to have the characteristic, her father must also have it. Her mother must have it or be a carrier.

• The characteristic often skips a generation from the grandfather to the grandson.

• If a woman has the characteristic, all of her sons will have it.

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Muscle DystrophyCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

(Abnormal): Courtesy Dr. Rabi Tawil, Director, Neuromuscular Pathology Laboratory, University of Rochester Medical Center; (Boy): Courtesy Muscular Dystrophy Association; (Normal): Courtesy Dr. Rabi Tawil, Director, Neuromuscular Pathology Laboratory, University of

Rochester Medical Center.

abnormalmuscle

normaltissue

fibroustissue

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Terminology

!Pleiotropy!A gene that affects more than one characteristic of an

individual!Sickle-cell (incomplete dominance)

!Codominance!More than one allele is fully expressed!ABO blood type (multiple allelic traits)

!Epistasis!A gene at one locus interferes with the expression of a

gene at a different locus!Human skin color (polygenic inheritance)

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Review

!Blending Inheritance!Monohybrid Cross

!Law of Segregation!Modern Genetics

!Genotype vs. Phenotype!Punnett Square

!Dihybrid Cross!Law of Independent Assortment

!Human Genetic Disorders

Sylvia S. Mader

Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or displayPowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor

BIOLOGY10th Edition

Mendelian Patterns of Inheritance

Chapter 11: pp. 189 - 210

49


Parents

eggs

Ee Ee

spem

Punn

ett s

quar

e

Offspring

E e

E

e

Ee

EeEE

ee

TT tt

tT

Tt

eggs

sper

m

Offspring

T t

T

t

TT Tt

Tt tt

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