09 Pptlecture Lec

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

PowerPoint Lectures forBiology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon

Lectures by Chris Romero

Chapter 9Chapter 9

Patterns of Inheritance


Purebreds and Mutts–A Difference of Heredity

• Purebred dogs

– Are very similar on a genetic level due to selective breeding


• Mutts, or mixed breed dogs on the other hand

– Show considerably more genetic variation


MENDEL’S LAWS

9.1 The science of genetics has ancient roots

• The historical roots of genetics, the science of heredity

– Date back to ancient attempts at selective breeding


9.2 Experimental genetics began in an abbey garden

• Modern genetics

– Began with Gregor Mendel’s quantitative experiments with pea plants

Petal

CarpelStamen

Figure 9.2 BFigure 9.2 A


• Mendel crossed pea plants that differed in certain characteristics

– And traced traits from generation to generation

Figure 9.2 C

1 Removed stamens from purple flower

2 Transferred pollen from stamens of white flower to carpel of purple flower

3 Pollinated carpel matured into pod

4 Planted seeds from pod

Offspring(F1)

Parents(P)

Purple

Carpel

White

Stamens


• Mendel hypothesized that there are alternative forms of genes

– The units that determine heritable traits

Flower color

Flower position

Seed color

Seed shape

Pod color

Pod shape

Stem length

Purple White

Axial Terminal

Round Wrinkled

Inflated Constricted

Tall Dwarf

GreenYellow

Green Yellow

Figure 9.2 D


9.3 Mendel’s law of segregation describes the inheritance of a single characteristic

• From his experimental data

– Mendel deduced that an organism has two genes (alleles) for each inherited characteristic

Figure 9.3 A

P generation(true-breedingparents)

F1 generation

F2 generation

Purple flowers White flowers

All plants havepurple flowers

Fertilizationamong F1 plants(F1 F1)

of plantshave purple flowers

34 of plants

have white flowers

14


• For each characteristic

– An organism inherits two alleles, one from each parent


• If the two alleles of an inherited pair differ

– Then one determines the organism’s appearance and is called the dominant allele

• The other allele

– Has no noticeable effect on the organism’s appearance and is called the recessive allele


• Mendel’s law of segregation

– Predicts that allele pairs separate from each other during the production of gametes

Figure 9.3 B

P plants

Gametes

Genetic makeup (alleles)

Gametes

F1 plants(hybrids)

F2 plants

PP pp

All P All p

All Pp

Sperm

12

P

P

P

p

p

PP Pp

Pp pp

EggsGenotypic ratio1 PP : 2 Pp: 1 pp

Phenotypic ratio3 purple : 1 white

12

p


9.4 Homologous chromosomes bear the two alleles for each characteristic

• Alternative forms of a gene

– Reside at the same locus on homologous chromosomes

Figure 9.4

Genotype: PP aa BbHeterozygous

P a b

P a B

Gene loci

Recessiveallele

Dominantallele

Homozygousfor thedominant allele

Homozygousfor therecessive allele


9.5 The law of independent assortment is revealed by tracking two characteristics at once

• By looking at two characteristics at once

– Mendel tried to determine how two characteristics were inherited


• Mendel’s law of independent assortment

– States that alleles of a pair segregate independently of other allele pairs during gamete formation

Figure 9.5 A

Hypothesis: Dependent assortment Hypothesis: Independent assortment

RRYY rryy

Gametes Gametes

RRYY rryy

RrYy RrYy

RY ry ryRY

Sperm Sperm

RY ry

ry

RY

ry

Ry

ry

RYRRYY

RrYY

RRYy

RrYy

RrYY

rrYY

RrYy

rrYy

RRYy

RrYy

RRyy

Rryy

RrYy

rrYy

Rryy

rryy

RY ry ryRY

Actual resultscontradict hypothesis

Actual resultssupport hypothesis

YellowroundGreenround

Yellowwrinkled

Greenwrinkled

Eggs

P generation

F1 generation

F2 generation

Eggs

12

12

12

12

14

14

14

14

14

14

14

14

916

316

3161

16


• An example of independent assortment

Black coat, normal visionB_N_

Black coat, blind (PRA)B_nn

Chocolate coat, normal visionbbN_

Chocolate coat, blind (PRA)bbnn

Blind Blind

9 black coat, normal vision

3 black coat,blind (PRA)

3 chocolate coat, normal vision

1 chocolate coat, blind (PRA)

BbNn BbNn

PhenotypesGenotypes

Mating of heterozygotes(black, normal vision)

Phenotypic ratioof offspring

Figure 9.5 B


9.6 Geneticists use the testcross to determine unknown genotypes

• The offspring of a testcross, a mating between an individual of unknown genotype and a homozygous recessive individual

– Can reveal the unknown’s genotype

Testcross:

Genotypes

Gametes

Offspring

B_ bb

Two possibilities for the black dog:

BB or Bb

B B b

b Bb b Bb bb

All black 1 black : 1 chocolateFigure 9.6


9.7 Mendel’s laws reflect the rules of probability

• Inheritance follows the rules of probability


• The rule of multiplication

– Calculates the probability of two independent events

• The rule of addition

– Calculates the probability of an event that can occur in alternate ways

Figure 9.7

F1 genotypes

Bb female

Formation of eggs

F2 genotypes

Bb male

Formation of sperm

B b

BB B B b

b b B b b

12

12

12

12

14

14

14

14


CONNECTION

9.8 Genetic traits in humans can be tracked through family pedigrees

• The inheritance of many human traits

– Follows Mendel’s lawsDominant Traits Recessive Traits

Freckles No freckles

Widow’s peak Straight hairline

Free earlobe Attached earlobe

Figure 9.8 A


• Family pedigrees

– Can be used to determine individual genotypes

DdJoshuaLambert

DdAbigailLinnell

D ?JohnEddy

D ?HepzibahDaggett

D ?Abigail

Lambert

ddJonathanLambert

DdElizabeth

Eddy

Dd Dd dd Dd Dd Dd dd

Female MaleDeafHearing

Figure 9.8 B


CONNECTION

9.9 Many inherited disorders in humans are controlled by a single gene

• Some autosomal disorders in humans

Table 9.9


Parents

Offspring

Sperm

NormalDd

NormalDd

D d

Eggs

D

d

DDNormal

DdNormal(carrier)

DdNormal(carrier)

ddDeaf

Figure 9.9 A

Recessive Disorders• Most human genetic disorders are recessive


Figure 9.9 B

Dominant Disorders

• Some human genetic disorders are dominant


CONNECTION

9.10 New technologies can provide insight into one’s genetic legacy

• New technologies

– Can provide insight for reproductive decisions


Identifying Carriers

• For an increasing number of genetic disorders

– Tests are available that can distinguish carriers of genetic disorders


Figure 9.10 A

Amniocentesis Chorionic villus sampling (CVS)

Ultrasoundmonitor

Fetus

Uterus

Amnioticfluid

Fetalcells

Severalweeks

Biochemicaltests

Severalhours

Fetalcells

Uterus

Cervix

Suction tube insertedthrough cervix to extracttissue from chorionic villi

Needle insertedthrough abdomen toextract amniotic fluid

Centrifugation

Ultrasoundmonitor

Fetus

Placenta

Chorionicvilli

Karyotyping

Placenta

Cervix

Fetal Testing• Amniocentesis and chorionic villus sampling (CVS)

– Allow doctors to remove fetal cells that can be tested for genetic abnormalities


Figure 9.10 B

Fetal Imaging• Ultrasound imaging

– Uses sound waves to produce a picture of the fetus


Newborn Screening

• Some genetic disorders can be detected at birth

– By simple tests that are now routinely performed in most hospitals in the United States


Ethical Considerations

• New technologies such as fetal imaging and testing

– Raise new ethical questions


VARIATIONS ON MENDEL’S LAWS

9.11 The relationship of genotype to phenotype is rarely simple

• Mendel’s principles are valid for all sexually reproducing species

– But genotype often does not dictate phenotype in the simple way his laws describe


9.12 Incomplete dominance results in intermediate phenotypes

• When an offspring’s phenotype is in between the phenotypes of its parents

– It exhibits incomplete dominance

Figure 9.12 A

P generation

F1 generation

F2 generation

RedRR

Gametes

Whiterr

Gametes

Sperm

Eggs

PinkRr

R

R

R

r

rR

r

r

RedRR

PinkrR

PinkRr

Whiterr

12

12

12

12

12

12

Genotypes:

HHHomozygous

for ability to makeLDL receptors

HhHeterozygous

hhHomozygous

for inability to makeLDL receptors

Phenotypes:

LDLLDLreceptor

Cell

Normal Mild disease Severe disease

Figure 9.12 B


9.13 Many genes have more than two alleles in the population

• In a population

– Multiple alleles often exist for a characteristic


• The ABO blood type in humans

– Involves three alleles of a single gene

• The alleles for A and B blood types are codominant

– And both are expressed in the phenotype

Figure 9.13

BloodGroup(Phenotype) Genotypes

AntibodiesPresent inBlood

Reaction When Blood from Groups Below Is Mixed withAntibodies from Groups at Left

O A B AB

O

A

B

AB

ii

IAIA

orIAi

IBIB

orIBi

IAIB

Anti-AAnti-B

Anti-B

Anti-A

—


9.14 A single gene may affect many phenotypic characteristics

• In pleiotropy

– A single gene may affect phenotype in many waysIndividual homozygous

for sickle-cell allele

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

Sickle-cell (abnormal) hemoglobin

Sickle cells

Breakdown ofred blood cells

Clumping of cellsand clogging of

small blood vessels

Accumulation ofsickled cells in spleen

Physicalweakness

Anemia Heartfailure

Pain andfever

Braindamage

Damage toother organs

Spleendamage

Impairedmentalfunction

ParalysisPneumoniaand otherinfections

Rheumatism Kidneyfailure

5,55

5

Figure 9.14


9.15 A single characteristic may be influenced by many genes

• Polygenic inheritance

– Creates a continuum of phenotypes

Figure 9.15

P generation

F1 generation

F2 generation

Sperm

Eggs

aabbcc(very light)

AABBCC(very dark)

AaBbCc AaBbCc

18

18

18

18

18

18

18

18

18

18

18

18

18

18

18

18

1 64

6 64

15 64

2064

1564

6 64

1 64

1 64

2064

15 64

6 64

Skin color

Fra

ctio

n of

pop

ulat

ion


9.16 The environmental affects many characteristics

• Many traits are affected, in varying degrees

– By both genetic and environmental factors

Figure 9.16


CONNECTION

9.17 Genetic testing can detect disease-causing alleles

• Predictive genetic testing

– May inform people of their risk for developing genetic diseases


THE CHROMOSOMAL BASIS OF INHERITANCE

9.18 Chromosome behavior accounts for Mendel’s laws

• Genes are located on chromosomes

– Whose behavior during meiosis and fertilization accounts for inheritance patterns


• The chromosomal basis of Mendel’s laws

All round yellow seeds(RrYy)

Metaphase Iof meiosis

(alternative arrangements)

Anaphase Iof meiosis

Metaphase IIof meiosis

Gametes

F1 generation

F2 generation

Fertilization among the F1 plants

(See Figure 9.5A)

1

4 RY

1

4ry

R

R

R

R RR

R

y

Y

Y

Y

Y Yy Y Y

r

r

y

R

Y

r

y

R r r r r

rr

y

r

Y

R

y

r

Y

R

y

1

4rY

1

4 Ry

9 : 3 : 3 : 1

y y y

yY

Figure 9.18


9.19 Genes on the same chromosome tend to be inherited together

• Certain genes are linked

– They tend to be inheritedtogether because they reside close together onthe same chromosome

Experiment

Explanation: linked genes

PpLI PpLILong pollen

Observed PredictionPhenotypes offspring (9:3:3:1)

Purple longPurple roundRed longRed round

Parentaldiploid cellPpLI

Most gametes

Mostoffspring Eggs

3 purple long : 1 red roundNot accounted for: purple round and red long

Meiosis

Fertilization

Sperm

284212155

215717124

P I

P L

P L

P L

P LP LP I

P L P I

P I

P L

P I

P I

P I

P I

P L

Purple flower

Figure 9.19


9.20 Crossing over produces new combinations of alleles

• Crossing over can separate linked alleles

– Producing gametes with recombinant chromosomes

A B

a b

Tetrad Crossing over

A B

A b

a b

a B

GametesFigure 9.20 A


• Thomas Hunt Morgan

– Performed some of the early studies of crossing over using the fruit fly Drosophila melanogaster

Figure 9.20 B


• Morgan’s experiments

– Demonstrated the roleof crossing over in inheritance

Figure 9.20 C

Experiment

Gray body,long wings(wild type)

GgLI

Female

Black body,vestigial wings

ggll

Male

Offspring Gray long

965 944 206 185

Black vestigial Gray vestigial Black long

Parentalphenotypes

Recombinantphenotypes

Recombination frequency = = 0.17 or 17%391 recombinants

2,300 total offspring

Explanation

GgLI(female)

ggll(male)

G L

g l

g l

g l

G L g l G l gL g l

Eggs Sperm

G L g lg l g l g l g l

LglG

Offspring


9.21 Geneticists use crossover data to map genes

• Morgan and his students

– Used crossover data to map genes in Drosophila

Figure 9.21 A


• Recombination frequencies

– Can be used to map the relative positions of genes on chromosomes.

Figure 9.21 B

Mutant phenotypes

Shortaristae

Blackbody(g)

Cinnabareyes(c)

Vestigialwings(l)

Browneyes

Long aristae(appendageson head)

Gray body(G)

Redeyes(C)

Normalwings(L)

Redeyes

Wild-type phenotypes

Chromosomeg c l

9% 9.5%

17%

Recombinationfrequencies

Figure 9.21 C


SEX CHROMOSOMES AND SEX-LINKED GENES

9.22 Chromosomes determine sex in many species

• In mammals, a male has one X chromosome and one Y chromosome

– And a female has two X chromosomes

(male) (female)

Parents’diploidcells

Sperm Egg

Offspring(diploid)

44+

XY

44+

XX

22+X

22+Y

22+X

44+

XX

44+

XY

Figure 9.22 A


• The Y chromosome

– Has genes for the development of testes

• The absence of a Y chromosome

– Allows ovaries to develop


• Other systems of sex determination exist in other animals and plants

22+

XX

22+X

76+

ZW

76+

ZZ

32 16

Figure 9.22 D

Figure 9.22 C

Figure 9.22 B


9.23 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


• In Drosophila

– White eye color is a sex-linked trait

Figure 9.23 A


• The inheritance pattern of sex-linked genes

– Is reflected in females and males

Female Male

Sperm

Xr Y

XR

Xr Y XR XR

XR Xr XR YEggs

R = red-eye alleler = white-eye allele

Female Male

Sperm

XR Y

XR

XR Y XR Xr

XR XR XR Y

Eggs

Xr Xr XR Xr Y

Female

Sperm

Xr Y

XR

Xr Y XR Xr

XR Xr XR Y

Eggs

Male

Xr Xr Xr Xr Y

Figure 9.23 B Figure 9.23 C Figure 9.23 D


CONNECTION

9.24 Sex-linked disorders affect mostly males

• Most sex-linked human disorders

– Are due to recessive alleles

– Are mostly seen in males

Queenvictoria

Albert

Alice Louis

Alexandra CzarNicholas IIof Russia

AlexisFigure 9.24 A Figure 9.24 B


• A male receiving a single X-linked allele from his mother

– Will have the disorder

• A female

– Has to receive the allele from both parents to be affected

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