powerlecture: chapter 20 observing patterns in inherited traits

PowerLecture:PowerLecture:Chapter 20Chapter 20

Observing Patterns in Observing Patterns in Inherited TraitsInherited Traits

Learning ObjectivesLearning Objectives

Be able to distinguish between “genes” and Be able to distinguish between “genes” and “alleles.”“alleles.”

Know Mendel’s principles of dominance, Know Mendel’s principles of dominance, segregation, and independent assortment.segregation, and independent assortment.

Understand how to solve genetics problems Understand how to solve genetics problems that involve monohybrid and dihybrid that involve monohybrid and dihybrid crosses.crosses.

Understand the variations that can occur in Understand the variations that can occur in observable patterns of inheritance.observable patterns of inheritance.

Learning Objectives (cont’d)Learning Objectives (cont’d)

Explain how a given pair of genes on Explain how a given pair of genes on homologous chromosomes can separate homologous chromosomes can separate during meiosis. during meiosis.

Impacts/IssuesImpacts/Issues

Designer Genes?Designer Genes?

Designer Genes? Designer Genes?

Our ability to tinker with genes Our ability to tinker with genes is growing all the time.is growing all the time.

Mapping of the human genome is Mapping of the human genome is pinpointing the locations of genes pinpointing the locations of genes on chromosomes.on chromosomes.

One result of this effort could be One result of this effort could be the correction of genetic defects, the correction of genetic defects, but another could be but another could be eugenic eugenic engineeringengineering..

Designer Genes? Designer Genes?

There may be moral and ethical concerns There may be moral and ethical concerns involved in deciding which forms of a trait involved in deciding which forms of a trait are more “desirable” or “acceptable” than are more “desirable” or “acceptable” than others.others.

Forty percent of Americans say it would be Forty percent of Americans say it would be acceptable to manipulate genes to make their acceptable to manipulate genes to make their children smarter or better looking.children smarter or better looking.

Eighteen percent of British parents said it would Eighteen percent of British parents said it would be all right to use genetic enhancement to be all right to use genetic enhancement to prevent children from being aggressive.prevent children from being aggressive.

Video: Genetics in SportsVideo: Genetics in Sports

This video clip is available in CNN Today This video clip is available in CNN Today Videos for Genetics, 2005, Volume VII. Videos for Genetics, 2005, Volume VII. Instructors, contact your local sales Instructors, contact your local sales representative to order this volume, while representative to order this volume, while supplies last.supplies last.

Useful References for Impacts/IssuesUseful References for Impacts/Issues

The latest references for topics covered in this section can be found at The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articleswww.thomsonedu.com to access InfoTrac articles. .

Washington PostWashington Post: Beyond Steroids: Designer : Beyond Steroids: Designer Genes For Unscrupulous AthletesGenes For Unscrupulous Athletes

InfoTrac: Designer Genes: Will DNA InfoTrac: Designer Genes: Will DNA Technology Let Parents Design Their Kids? Technology Let Parents Design Their Kids? Ingrid Wickelgren. Ingrid Wickelgren. Current Science, Current Science, Dec. 3, Dec. 3, 2004.2004.

How Would You Vote?How Would You Vote?To conduct an instant in-class survey using a classroom response To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main system, access “JoinIn Clicker Content” from the PowerLecture main menu. menu.

Would you favor legislation that limits or Would you favor legislation that limits or prohibits engineering genes except for health prohibits engineering genes except for health reasons?reasons? a. Yes, parents should accept their children as a. Yes, parents should accept their children as

they are.they are. b. No, parents should have the right to choose b. No, parents should have the right to choose

the kind of child they want to raise. the kind of child they want to raise.

Useful References for Useful References for How Would You Vote?How Would You Vote?


InfoTrac: The Science and Politics of InfoTrac: The Science and Politics of Genetically Modified Humans. Richard Genetically Modified Humans. Richard Hayes. Hayes. World Watch, World Watch, July–Aug. 2002.July–Aug. 2002.

InfoTrac: Who Gets the Good Genes? Robert InfoTrac: Who Gets the Good Genes? Robert Wright. Wright. TimeTime, Jan. 11, 1999., Jan. 11, 1999.

InfoTrac: To Build a Baby. Fred Guterl. InfoTrac: To Build a Baby. Fred Guterl. Newsweek International, Newsweek International, June 30, 2003.June 30, 2003.

Section 1Section 1

Basic Concepts Basic Concepts

of Heredityof Heredity

Basic Concepts of Heredity Basic Concepts of Heredity

Gregor Mendel used experiments in plant Gregor Mendel used experiments in plant breeding to investigate how sexually breeding to investigate how sexually reproducing organisms inherited traits; he reproducing organisms inherited traits; he hypothesized that “factors” from each parent hypothesized that “factors” from each parent were the units of heredity and formulated were the units of heredity and formulated early ideas concerning how they were early ideas concerning how they were passed on. passed on.

Animation: Crossing Garden Pea PlantsAnimation: Crossing Garden Pea Plants

CLICKTO PLAY


The following express Mendel’s ideas in The following express Mendel’s ideas in modern language.modern language.

GenesGenes carry encoded carry encoded information about information about specific traits; each gene has a specific specific traits; each gene has a specific locuslocus on a on a chromosome.chromosome.

Diploid cells have two genes (a gene pair) for Diploid cells have two genes (a gene pair) for each trait—each on a homologous each trait—each on a homologous chromosome.chromosome.

AllelesAlleles are various molecular forms of a gene are various molecular forms of a gene for the same trait.for the same trait.

Identical alleles are said to be Identical alleles are said to be homozygoushomozygous; if ; if the alleles differ, they are the alleles differ, they are heterozygousheterozygous..

Animation: Genetic TermsAnimation: Genetic Terms

CLICKTO PLAY

© 2007 Thomson Higher Education

a A pair of homologous chromosomes, each in the unduplicated state (most often, one from a male parent and its partner from a female parent)

b A gene locus (plural, loci) the location for a specific gene on a specific type of chromosome

c A pair of alleles (each being one chemical form of a gene) at corresponding loci on a pair of homologous chromosomes

d Three pairs of genes (at three loci on this pair of homologous chromosomes) same thing as three pairs of alleles

Fig. 20.1, p. 374


DominantDominant (A) alleles mask the effect of (A) alleles mask the effect of recessiverecessive (a) alleles. (a) alleles.

Thus, Thus, homozygous dominanthomozygous dominant = AA, = AA, homozygous recessivehomozygous recessive = aa, and = aa, and heterozygousheterozygous =Aa. =Aa.

GenotypeGenotype refers to refers to

the sum of the genes the sum of the genes

we inherit, and we inherit, and

phenotypephenotype is how is how

the genes are the genes are

expressed (what you observe).expressed (what you observe).

Useful References for Section 1Useful References for Section 1


Genetics Society of America: Genetics Society of America: GeneticsGenetics InfoTrac: Darwin Would Have Loved It. InfoTrac: Darwin Would Have Loved It.

Michael J. Novacek. Michael J. Novacek. TimeTime, April 17, 2006., April 17, 2006.

Section 2Section 2

One Chromosome, One One Chromosome, One Copy of a GeneCopy of a Gene

©2007 Thomson Higher Education

One Chromosome, One Copy of a Gene One Chromosome, One Copy of a Gene

Mendel hypothesized that each diploid Mendel hypothesized that each diploid organism inherits two units for each trait, organism inherits two units for each trait, one from each parent.one from each parent.

C C c c

ccCCParents:

(meiosis)

Gametes:

(meiosis)

In-text Fig, p. 375In-text Fig, p. 375

One Chromosome, One Copy of a Gene One Chromosome, One Copy of a Gene

His first experiment to show this was the His first experiment to show this was the monohybrid crossmonohybrid cross..

Monohybrid crosses have two parents, P, that Monohybrid crosses have two parents, P, that are true-breeding for contrasting forms of a are true-breeding for contrasting forms of a trait, that is CC and cc.trait, that is CC and cc.

Mendel discovered that each gene segregates Mendel discovered that each gene segregates from the other during meiosis such that each from the other during meiosis such that each gamete will receive only one gene per trait.gamete will receive only one gene per trait.

This separation of genes is the This separation of genes is the principle of principle of segregationsegregation..


fertilization produces heterozygous offspring

meiosis II

meiosis I

(chromosomes duplicated before

meiosis)

homozygous-dominant parent homozygous-recessive parent

gametes gametes

Fig. 20.4, p. 375

fertilization produces heterozygous offspring

meiosis II

meiosis I

(chromosomes duplicated before

meiosis)

homozygous-dominant parent homozygous-recessive parent

gametes gametes

Fig. 20.4, p. 375

Stepped Art

Animation: Chromosome SegregationAnimation: Chromosome Segregation

CLICKTO PLAY



InfoTrac: Human Chromosome 3 Is InfoTrac: Human Chromosome 3 Is Sequenced. Sequenced. UPI NewsTrackUPI NewsTrack, April 27, 2006., April 27, 2006.

Section 3Section 3

Figuring Genetic Figuring Genetic ProbabilitiesProbabilities

Figuring Genetic Probabilities Figuring Genetic Probabilities

The parental generation in a cross is The parental generation in a cross is designated designated PP; the children are ; the children are FF11 (first filial); (first filial);

the grandchildren are the the grandchildren are the FF22 (second filial) (second filial)

generation.generation. A A Punnett squarePunnett square can be used to predict can be used to predict

the result of a genetic cross.the result of a genetic cross.

female gametes (n)(eggs)

mal

e g

amet

es (

n)

(sp

erm

)C c

C

c cc

C c

C

c ccCc

Cc

C c

ccCc

C

c

C c

ccCc

CcCCC

c

Fig 20.5, p. 376


With a monohybrid cross for two heterozygous With a monohybrid cross for two heterozygous parents (Cc), four outcomes are possible each parents (Cc), four outcomes are possible each time a sperm fertilizes an egg.time a sperm fertilizes an egg.

• Each parent produces C gametes and c gametes.Each parent produces C gametes and c gametes.• Put together, the offspring show a 3:1 phenotypic Put together, the offspring show a 3:1 phenotypic

ratio indicating that 75% of the time the child will ratio indicating that 75% of the time the child will have the dominant trait (either CC or Cc).have the dominant trait (either CC or Cc).


Fig. 20.6 (1), p. 377

F1 phenotypes

Parent:homozygousrecessive

Alleles segregate

Parent:homozygousdominant

Cc Cc

Cc Cc

CC

C

C

cc

c c

c c

C

C

Cc Cc

Cc Cc


Fig. 20.6 (2), p. 377

F2

phenotypesF1

offspring:

F1

offspring: CC Cc

Cccc

CC Cc

Cc cc

3 dominant (CC, Cc, Cc)1 recessive (cc)

Cc

C

c

C

c

Cc

C c

C c

Animation: Monohybrid CrossAnimation: Monohybrid Cross

CLICKTO PLAY

Animation: Three-to-One RatioAnimation: Three-to-One Ratio

CLICKTO PLAY


Fertilization depends on probability. Fertilization depends on probability. • ProbabilityProbability is a number between 0 and 1 that is a number between 0 and 1 that

indicates the likelihood that something will happen (if indicates the likelihood that something will happen (if 0, it never happens; if 1, it always happens).0, it never happens; if 1, it always happens).

• Thus, each new organism has a probability of three Thus, each new organism has a probability of three chances in four of having at least one dominant allele chances in four of having at least one dominant allele in the above example.in the above example.

Figuring Genetic Figuring Genetic Probabilities Probabilities

It is important to It is important to remember two things remember two things about genetic probability:about genetic probability:

• Probability is not the same Probability is not the same as possibility; that is, the as possibility; that is, the outcomes predicted by outcomes predicted by probability don’t have to probability don’t have to turn up in a given family.turn up in a given family.

• Probability does not Probability does not change; that is, the change; that is, the probability of having a son probability of having a son or daughter is always 50% or daughter is always 50% no matter how many total no matter how many total children you bear.children you bear.

Figure 20.7Figure 20.7

Animation: Genotypes Animation: Genotypes Variation CalculatorVariation Calculator

CLICKTO PLAY


A testcross also can reveal genotypes.A testcross also can reveal genotypes. To determine an unknown genotype (a question To determine an unknown genotype (a question

of whether it is homozygous dominant [DD] or of whether it is homozygous dominant [DD] or heterozygous [Dd]) a heterozygous [Dd]) a testcrosstestcross is done is done between the organism in question and a known between the organism in question and a known recessive (dd).recessive (dd).

If any recessive offspring are produced, then If any recessive offspring are produced, then the organism in question can be designated the organism in question can be designated heterozygous.heterozygous.

Animation: TestcrossAnimation: Testcross

CLICKTO PLAY



InfoTrac: Advances in Preconception Genetic InfoTrac: Advances in Preconception Genetic Counseling. Marta C. Wille. Counseling. Marta C. Wille. Journal of Journal of Perinatal & Neonatal NursingPerinatal & Neonatal Nursing, Jan.–Mar. , Jan.–Mar. 2004.2004.

Section 4Section 4

How Genes for Different How Genes for Different Traits Are Sorted into Traits Are Sorted into

GametesGametes

How Genes for Different Traits Are Sorted How Genes for Different Traits Are Sorted into Gametesinto Gametes

The Mendelian principle of The Mendelian principle of independent independent assortmentassortment states that each gene of a pair states that each gene of a pair tends to assort into gametes independently tends to assort into gametes independently of other gene pairs located on of other gene pairs located on nonhomologous chromosomes.nonhomologous chromosomes.

Evidence for independent assortment was Evidence for independent assortment was obtained from obtained from dihybrid crossesdihybrid crosses, crosses , crosses involving two traits at a time where simple involving two traits at a time where simple dominance exists.dominance exists.

How Genes for Different Traits Are Sorted How Genes for Different Traits Are Sorted into Gametesinto Gametes

There are 16 possible allele combinations in the There are 16 possible allele combinations in the offspring when each parent is heterozygous for offspring when each parent is heterozygous for two traits.two traits.

If we look at chin fissure and dimples as being If we look at chin fissure and dimples as being dominant, then the probable phenotypic ratio dominant, then the probable phenotypic ratio for a cross between heterozygotes is 9:3:3:1 (9 for a cross between heterozygotes is 9:3:3:1 (9 with chin fissure and dimples; 3 with chin with chin fissure and dimples; 3 with chin fissure but no dimples; 3 with a smooth chin fissure but no dimples; 3 with a smooth chin and dimples; 1 with a smooth chin and no and dimples; 1 with a smooth chin and no dimples).dimples).

Animation: Independent AssortmentAnimation: Independent Assortment

CLICKTO PLAY


Fig. 20.8, p. 378

Nucleus of a diploid (2n) germ cells with two pairs of homologous chromosomes

OR

a. Possible alignments of the two homologous chromosomes during metaphase I of meiosis

b. The resulting alignments atmetaphase II

c. Allele combinations possible in gametes

1/4 CD 1/4 cd 1/4 Cd 1/4 cD

Animation: Dyhibrid CrossAnimation: Dyhibrid Cross

CLICKTO PLAY

Dyhibrid CrossDyhibrid Cross

Figures 20.9 and 20.10Figures 20.9 and 20.10



InfoTrac: Germline Susceptibility to InfoTrac: Germline Susceptibility to Colorectal Cancer Due to Base-Excision Colorectal Cancer Due to Base-Excision Repair Gene Defects. Susan M. Farrington et Repair Gene Defects. Susan M. Farrington et al. al. American Journal of Human GeneticsAmerican Journal of Human Genetics, , July 2005.July 2005.

Section 5Section 5

Single Genes, Single Genes,

Varying EffectsVarying Effects

Single Genes, Varying Effects Single Genes, Varying Effects

One gene may affect several traits.One gene may affect several traits. PleiotropyPleiotropy occurs when a single gene affects occurs when a single gene affects

two or more aspects of the phenotype.two or more aspects of the phenotype. The recessive condition The recessive condition CHHCHH (cartilage-hair (cartilage-hair

hypoplasia) occurs following mutation to a gene hypoplasia) occurs following mutation to a gene called RMRP; individuals commonly have little called RMRP; individuals commonly have little body hair, abnormally short limbs, loose body hair, abnormally short limbs, loose ligaments, and immunological dysfunction.ligaments, and immunological dysfunction.

Fig 20.11, p. 380

leads to multipleeffects

Sparse bodyhair

Abnormallyshort stature,loose ligaments

Weak cellularimmunity,susceptibilityto lymphatic cancer

Mutation of RMRP geneon chromosome 9

Skin Skeleton Immunesystem


In another example, the gene for In another example, the gene for sickle-cell sickle-cell anemiaanemia codes for a variant form of hemoglobin, codes for a variant form of hemoglobin, which in turn not only affects the shape of the which in turn not only affects the shape of the red blood cells, but produces perhaps a dozen red blood cells, but produces perhaps a dozen other effects; individuals with other effects; individuals with sickle-cell traitsickle-cell trait (i.e. they are heterozygous for the gene) (i.e. they are heterozygous for the gene) generally do not have symptoms. generally do not have symptoms.

Figure 20.12aFigure 20.12a

Fig 20.12c, p. 381

Normal HbA

One amino acidsubstituted inhemoglobin

glu

val

pro

thr

leu

his

val

glu

val

pro

thr

leu

his

val

Sickle-cell HbS

Animation: Symptoms of Animation: Symptoms of Sickle-Cell AnemiaSickle-Cell Anemia

CLICKTO PLAY

Fig 20.12b, p. 381

overactivity ofbone marrow

homozygous recessive individual ( HbS/ HbS)

abnormal hemoglobin

sickling of red blood cells

collection of sicklecells in the spleen

clumping of cells andinterference withblood circulation

local failures in blood supply

enlargement,then fibrosis

of spleen

paralysispneumoniakidneyfailure

lungdamage

gastrointestinaltract damage

muscle andjoint damage

braindamage

kidneydamage

heartdamage

abdominalpain

skulldeformation

impairedmental

functionheart failure rheumatism

rapid destructionof sickle cells

dilationof heart

increase in amountof bone marrow

poor physicaldevelopment

weaknessand fatigue

anemia

Animation: Overview of Animation: Overview of Sickle-Cell AnemiaSickle-Cell Anemia

CLICKTO PLAY


In codominance, more than one allele of a In codominance, more than one allele of a gene is expressed.gene is expressed.

In In codominancecodominance, both of the alleles for a given , both of the alleles for a given trait are expressed; this occurs in people trait are expressed; this occurs in people heterozygous for alleles that confer A and B heterozygous for alleles that confer A and B blood types.blood types.

In the ABO blood typing system, there are three In the ABO blood typing system, there are three alleles: two that are dominant (alleles: two that are dominant (IAIA and and IBIB) and ) and one that is recessive (one that is recessive ( ii).).

In situations where there are more than two In situations where there are more than two forms of the gene, we call it a forms of the gene, we call it a multiple allele multiple allele systemsystem..



InfoTrac: Pleiotropy and the Genomic InfoTrac: Pleiotropy and the Genomic Location of Sexually Selected Genes. Mark J. Location of Sexually Selected Genes. Mark J. FitzpatrickFitzpatrick. The American Naturalist. The American Naturalist, June , June 2004.2004.

InfoTrac: Bone Area and Bone Mineral InfoTrac: Bone Area and Bone Mineral Content Deficits in Children with Sickle Cell Content Deficits in Children with Sickle Cell Disease. Anne M. Buison et al. Disease. Anne M. Buison et al. PediatricsPediatrics, , Oct. 2005.Oct. 2005.

Section 6Section 6

Other Gene Impacts Other Gene Impacts and Interactionsand Interactions

Other Gene Impacts and Interactions Other Gene Impacts and Interactions

PenetrancePenetrance refers to the probability that refers to the probability that someone inheriting an allele will have the someone inheriting an allele will have the phenotype associated with that allele.phenotype associated with that allele.

A given phenotype can vary by different A given phenotype can vary by different degrees from one individual to the next in a degrees from one individual to the next in a population—the result of interactions with other population—the result of interactions with other genes and environmental influences.genes and environmental influences.


Several examples illustrate penetrance:Several examples illustrate penetrance:• Cystic fibrosis, caused by a recessive gene, is Cystic fibrosis, caused by a recessive gene, is

completely penetrant.completely penetrant.• PolydactylyPolydactyly and and campodactylycampodactyly are incompletely are incompletely

penetrant and show “variable expressivity.”penetrant and show “variable expressivity.”



Polygenic traits: several genes combined.Polygenic traits: several genes combined. Most traits are Most traits are polygenicpolygenic—they result from the —they result from the

combined expression of two or more genes; combined expression of two or more genes; skin and eye color are examples.skin and eye color are examples.


Many traits show Many traits show continuous variationcontinuous variation (example: height in humans).(example: height in humans).


Animation: Height Bar GraphAnimation: Height Bar Graph

CLICKTO PLAY


Do genes “program” behavior?Do genes “program” behavior? There is strong evidence that certain basic There is strong evidence that certain basic

human behaviors are genetically programmed.human behaviors are genetically programmed. Human behavior is so complex, however, that it Human behavior is so complex, however, that it

is difficult to design experiments to answer the is difficult to design experiments to answer the question conclusively.question conclusively.

Useful References for Section 6 Useful References for Section 6


InfoTrac: Disease Versus Disease. E. InfoTrac: Disease Versus Disease. E. Richard Stiehm. Richard Stiehm. PediatricsPediatrics, Jan. 2006., Jan. 2006.

InfoTrac: Mitochondrial Disease. Anthony InfoTrac: Mitochondrial Disease. Anthony H.V. Schapira. H.V. Schapira. The LancetThe Lancet, July 1, 2006., July 1, 2006.

American Psychological Association: American Psychological Association: Searching for Genes That Explain Our Searching for Genes That Explain Our PersonalitiesPersonalities

NPR: Genes and BehaviorNPR: Genes and Behavior

Section 7Section 7

Searching for Searching for Custom CuresCustom Cures

Each of us, because of our Each of us, because of our own personal mix of alleles, own personal mix of alleles, responds differently to responds differently to therapeutic drugs; the field therapeutic drugs; the field of of pharmacogeneticspharmacogenetics aims at pinpointing the aims at pinpointing the relationship between relationship between genetic variation and genetic variation and response to medications.response to medications.

Searching for Custom Cures Searching for Custom Cures


Once genes that control reactions to drugs Once genes that control reactions to drugs are identified, it will become easier and are identified, it will become easier and easier to match therapy to need while at the easier to match therapy to need while at the same time limiting side effects.same time limiting side effects.

Searching for Custom Cures Searching for Custom Cures

Useful References for Section 7 Useful References for Section 7


InfoTrac: Scientific, Ethical Questions InfoTrac: Scientific, Ethical Questions Temper Pharmacogenetics. Karen Young Temper Pharmacogenetics. Karen Young Kreeger. Kreeger. The ScientistThe Scientist, June 11, 2001., June 11, 2001.

InfoTrac: A Target for Iressa: The Fall and InfoTrac: A Target for Iressa: The Fall and Rise (And Fall) of a Pharmacogenetics Rise (And Fall) of a Pharmacogenetics Poster Child. David Secko. Poster Child. David Secko. The ScientistThe Scientist, , April 2006.April 2006.

powerlecture: chapter 20 observing patterns in inherited traits

Documents

engineering genes

locations of genes

impactsissuesdesigner

good genes

given pair of genes

infotrac articles

useful references

playbasic concepts of