Chapter 9•Each of the characters Mendel studied occurred in two distinct traits. In an Abbey...

© 2013 Pearson Education, Inc.Lectures by Edward J. Zalisko

PowerPoint® Lectures forCampbell Essential Biology, Fifth Edition, and

Campbell Essential Biology with Physiology,

Fourth Edition

– Eric J. Simon, Jean L. Dickey, and Jane B. Reece

Chapter 9Patterns of Inheritance

20_02SeaLion_SV.mpg

• People have selected and mated dogs with

preferred traits for more than 15,000 years.

• Over thousands of years, such genetic tinkering

has led to the incredible variety of body types

and behaviors in dogs today.

• The biological principles underlying genetics

have only recently been understood.

Biology and Society: Our Longest-Running Genetic Experiment: Dogs

© 2013 Pearson Education, Inc.

Figure 9.0

• Heredity is the transmission of traits from one

generation to the next.

• Genetics is the scientific study of heredity.

• Gregor Mendel

– worked in the 1860s,

– was the first person to analyze patterns of

inheritance, and

– deduced the fundamental principles of genetics.

HERITABLE VARIATION AND PATTERNS OF INHERITANCE


Figure 9.1

In an Abbey Garden

• Mendel studied garden peas because they

– were easy to grow,

– came in many readily distinguishable varieties,

– are easily manipulated, and

– can self-fertilize.


Figure 9.3-3

Removedstamensfrom purpleflower.

Stamens

Transferred pollen fromstamens of white flower

to carpel of purple flower.

Parents

(P)

Carpel

Offspring

(F1)

Pollinated carpel

matured into pod.

Planted seeds

from pod.

4

3

2

1

• A character is a heritable feature that varies

among individuals.

• A trait is a variant of a character.

• Each of the characters Mendel studied occurred in

two distinct traits.

In an Abbey Garden


• Mendel

– created purebred varieties of plants and

– crossed two different purebred varieties.

In an Abbey Garden


• Hybrids are the offspring of two different

purebred varieties.

– The parental plants are the P generation.

– Their hybrid offspring are the F1 generation.

– A cross of the F1 plants forms the F2 generation.

In an Abbey Garden


Mendel’s Law of Segregation

• Mendel performed many experiments.

• He tracked the inheritance of characters that occur

as two alternative traits.


Figure 9.4

WhitePurple

RecessiveDominant

Green Yellow

Terminal Axial

Wrinkled Round

Green Yellow

Seed

shape

Seed

color

Flower

position

Flower

color

Pod

color

RecessiveDominant

Pod

shape

Stem

length

Inflated Constricted

Tall Dwarf

Figure 9.4a

Monohybrid Crosses

• A monohybrid cross is a cross between purebred

parent plants that differ in only one character.


Figure 9.5-3

Purple flowers

F1 Generation

White flowers

P Generation(purebredparents)

All plants havepurple flowers

F2 Generation

Fertilization

among F1 plants

(F1 F1)

of plants

have purple flowers

of plants

have white flowers

34

14

Figure 9.5a

• Mendel developed four hypotheses from the

monohybrid cross, listed here using modern

terminology (including “gene” instead of “heritable

factor”).

1. The alternative versions of genes are called

alleles.

Monohybrid Crosses


2. For each inherited character, an organism inherits

two alleles, one from each parent.

– An organism is homozygous for that gene if both

alleles are identical.

– An organism is heterozygous for that gene if the

alleles are different.

Monohybrid Crosses


3. If two alleles of an inherited pair differ,

– then one determines the organism’s appearance

and is called the dominant allele and

– the other has no noticeable effect on the organism’s

appearance and is called the recessive allele.

Monohybrid Crosses


4. Gametes carry only one allele for each inherited

character.

– The two alleles for a character segregate (separate)

from each other during the production of gametes.

– This statement is called the law of segregation.

Monohybrid Crosses


• Do Mendel’s hypotheses account for the 3:1 ratio

he observed in the F2 generation?

• A Punnett square highlights

– the four possible combinations of gametes and

– the four possible offspring in the F2 generation.

Monohybrid Crosses


Figure 9.6P Generation Genetic makeup (alleles)

Alleles carried

by parents

Gametes

Purple flowers

PP

White flowers

pp

All P All p

pP

F1 Generation

(hybrids)

F2 Generation

(hybrids)

Alleles

segregate

Gametes

Purple flowers

All Pp

21

21

Sperm from

F1 plant

Eggs from

F1 plant

Phenotypic ratio

3 purple : 1 white

Genotypic ratio

1 PP : 2 Pp : 1 pp

p

p

P

PPP Pp

Pp pp

• Geneticists distinguish between an organism’s

physical appearance and its genetic makeup.

– An organism’s physical appearance is its

phenotype.

– An organism’s genetic makeup is its genotype.

Monohybrid Crosses


Genetic Alleles and Homologous Chromosomes

• A gene locus is a specific location of a gene along

a chromosome.

• Homologous chromosomes have alleles (alternate

versions) of a gene at the same locus.


Figure 9.7

Homologous

chromosomes

P

Genotype:

Gene loci

P

a

aa

b

B

Dominant

allele

Recessive

alleleBbPP

Homozygous

for the

dominant allele

Homozygous

for the

recessive allele

Heterozygous

with one dominant

and one recessive

allele

a

Figure 9.UN01

Meiosis

Haploid gametes

(allele pairs separate)

Diploid cell

(contains paired

alleles, alternate

forms of a gene)

Diploid zygote

(contains

paired alleles)

Gamete

from other

parent

Alleles

Fertilization

Mendel’s Law of Independent Assortment

• A dihybrid cross is the mating of parental

varieties differing in two characters.

• What would result from a dihybrid cross? Two

hypotheses are possible:

1. dependent assortment or

2. independent assortment.


Figure 9.8

F1 Generation

F2 Generation

RRYY

Predicted results

(not actually seen)

P Generation

Gametes RY

rryy

ry

(a) Hypothesis: Dependent assortment

RrYy

RY ry

Sperm

EggsEggs

RY

ry

Actual results

(support hypothesis)

RRYY

RY

rryy

ry

RrYy

(b) Hypothesis:

Independent assortment

Gametes

RY ry

Sperm

RY

ry

Ry

rY

RyrY

RRYY

RryyRRyyRrYyRRYy

RrYy rrYy Rryy rryy

RrYY

RrYY rrYY RrYy rrYy

RRYy RrYy

Yellowround

Yellowwrinkled

Greenwrinkled

Greenround

16

1

16

3

16

3

16

9

4

1

4

1

4

1

4

1

4

1

4

1

4

1

4

1

2

1

2

1

2

1

2

1

• Mendel’s dihybrid cross supported the hypothesis

that each pair of alleles segregates independently

of the other pairs during gamete formation.

• Thus, the inheritance of one character has no

effect on the inheritance of another.

• This is called Mendel’s law of independent

assortment.

• Independent assortment is also seen in two

hereditary characters in Labrador retrievers.

Mendel’s Law of Independent Assortment


Figure 9.9Blind dog

Phenotypes

(a) Possible phenotypes of Labrador retrievers

B_N_

Blind dog

Genotypes

(b) A Labrador dihybrid cross

Black coat,

normal visionB_nn

Black coat,

blind (PRA)

bbnn

Chocolate coat,blind (PRA)

bbN_

Chocolate coat,

normal vision

Mating of double heterozygotes

(black coat, normal vision)

BbNn BbNn

Phenotypicratio ofoffspring

9 black coat,

normal vision

3 black coat,

blind (PRA)

3 chocolate coat,

normal vision

1 chocolate coat,

blind (PRA)

Blind Blind

Using a Testcross to Determine an Unknown Genotype

• A testcross is a mating between

– an individual of dominant phenotype (but unknown

genotype) and

– a homozygous recessive individual.


Figure 9.UN02

Phenotype

Phenotype

Genotype

Conclusion

RecessiveDominantppP ?

All dominant

or

Unknown parent

is PP

1 dominant : 1 recessive

Unknown parent

is Pp

Figure 9.10

Two possible genotypes for the black dog:

B_ bb

Testcross

Genotypes

Bb

B b

orBB

B

b Bb Bb bbb

Gametes

Offspring All black 1 black : 1 chocolate

The Rules of Probability

• Mendel’s strong background in mathematics

helped him understand patterns of inheritance.

• The rule of multiplication states that the

probability of a compound event is the product of

the separate probabilities of the independent

events.


Figure 9.11

F1 Genotypes

F2 Genotypes

Bb female Bb male

Formation of eggs Formation of sperm

Male

gametes

Fem

ale

gam

ete

s

2

1

2

1

2

1

2

1

2

1

2

14

1

4

1

4

1

4

1

( )

B

BB B B

B

b

b

b b b b

Family Pedigrees

• Mendel’s principles apply to the inheritance of

many human traits.


Figure 9.12

DO

MIN

AN

T T

RA

ITS

Free earlobe

RE

CE

SS

IVE

TR

AIT

S

Widow’s peakFreckles

Attached earlobeStraight hairlineNo freckles

• Dominant traits are not necessarily

– normal or

– more common.

• Wild-type traits are

– those seen most often in nature and

– not necessarily specified by dominant alleles.

Family Pedigrees


• A family pedigree

– shows the history of a trait in a family and

– allows geneticists to analyze human traits.

Family Pedigrees


Figure 9.13

Female Male

Attached Free

Female Male

First generation(grandparents)

Second generation(parents, aunts, anduncles)

Third generation(brother andsister)

AaronFf

BettyFf

Cletusff

DebraFf

EvelynFForFf

LisaFForFf

Fredff

Gabeff

HalFf

InaFf

Jillff

Kevinff

Figure 9.13a

Human Disorders Controlled by a Single Gene

• Many human traits

– show simple inheritance patterns and

– are controlled by single genes on autosomes.


Table 9.1

Recessive Disorders

• Most human genetic disorders are recessive.

• Individuals who have the recessive allele but

appear normal are carriers of the disorder.


Figure 9.14

Parents

Offspring

DdHearing Hearing

Dd

Sperm

Eggs

D

HearingD

Dd

d

Hearing

(carrier)

DD

DdHearing

(carrier)

dd

Deafd

• Cystic fibrosis is

– the most common lethal genetic disease in the

United States and

– caused by a recessive allele carried by about one

in 31 Americans.

Recessive Disorders


• Prolonged geographic isolation of certain

populations can lead to inbreeding, the mating of

close relatives.

• Inbreeding increases the chance of offspring that

are homozygous for a harmful recessive trait.

Recessive Disorders


Dominant Disorders

• Some human genetic disorders are dominant.

– Achondroplasia is a form of dwarfism.

– The homozygous dominant genotype causes

death of the embryo.

– Thus, only heterozygotes have this disorder.

– Huntington’s disease, which leads to

degeneration of the nervous system, does not

usually begin until middle age.


Figure 9.15

Figure 9.16

Parents

Sperm

Eggs

d

DwarfD

Dd

d

Dd

ddd

Normal

(no achondroplasia) Molly JoDwarf

(achondroplasia)Dddd

Normaldd

Normal

DwarfMatt AmyJacob Zachary

Jeremy

The Process of Science: What Is the Genetic Basis of Coat Variation in Dogs?

• Observation: Dogs come in a wide variety of physical

types.

• Question: What is the genetic basis for canine coats?

• Hypothesis: A comparison of genes of a wide variety

of dogs with different coats would identify the genes

responsible.


• Prediction: Mutations in just a few genes account for

the coat appearance.

• Experiment: Compared DNA sequences of 622 dogs

from dozens of breeds.

• Results: Three genes in different combinations

produced seven different coat appearances, from very

short hair to full, thick, wired hair.

The Process of Science: What Is the Genetic Basis of Coat Variation in Dogs?


Figure 9.17

Genetic Testing

• Today many tests can detect the presence of

disease-causing alleles.

• Most genetic tests are performed during

pregnancy.

– Amniocentesis collects cells from amniotic fluid.

– Chorionic villus sampling removes cells from

placental tissue.

• Genetic counseling helps patients understand the

results and implications of genetic testing.


VARIATIONS ON MENDEL’S LAWS

• Some patterns of genetic inheritance are not

explained by Mendel’s laws.


Incomplete Dominance in Plants and People

• In incomplete dominance, F1 hybrids have an

appearance between the phenotypes of the two

parents.


Figure 9.UN03

Dominant phenotype

(RR)

Recessive phenotype

(rr)

Intermediate phenotype

(incomplete dominance)

(Rr)

Figure 9.18-3

F1 Generation

RR rr

Gametes

P Generation

F2 Generation Sperm

Gametes

Red White

R r

RrPink

R r

R r

R

r

RR Rr

rrRr

Eggs

21

21

21

21

21

21

• Hypercholesterolemia

– is a human trait that is an example of incomplete

dominance and

– is characterized by dangerously high levels of

cholesterol in the blood.



• In hypercholesterolemia,

– heterozygotes have blood cholesterol levels about twice normal, and

– homozygotes have about five times the normal amount of blood cholesterol and may have heart attacks as early as age 2.



Figure 9.19

Homozygousfor ability to make

LDL receptors

Severe diseaseMild disease

Cell

LDLreceptor

LDL

Homozygousfor inability to make

LDL receptors

HeterozygousHH Hh hh

GE

NO

TY

PE

PH

EN

OT

YP

E

Normal

ABO Blood Groups: An Example of Multiple Alleles and Codominance

• The ABO blood groups in humans are an

example of multiple alleles.

• The immune system produces blood proteins

called antibodies that bind specifically to foreign

carbohydrates.


• If a donor’s blood cells have a carbohydrate (A or B) that is foreign to the recipient, the blood cells may clump together, potentially killing the recipient.

• The clumping reaction is the basis of a blood-typing lab test.

• The human blood type alleles IA and IB are codominant, meaning that both alleles are expressed in heterozygous individuals who have type AB blood.

ABO Blood Groups: An Example of Multiple Alleles and Codominance


Figure 9.20

BloodGroup(Phenotype) OGenotypes

AntibodiesPresent inBloodRed Blood Cells

Reactions When Blood from Groups Below

Is Mixed with Antibodies from Groups at Left

A B AB

O

A

B

AB

ii

IAIB

IBIB

or

IBi

IAIA

or

IAi

Carbohydrate

A

Carbohydrate

BAnti-A

Anti-B

Anti-A

Anti-B

—

Pleiotropy and Sickle-Cell Disease

• Pleiotropy is when one gene influences several

characters.

• Sickle-cell disease

– exhibits pleiotropy,

– results in abnormal hemoglobin proteins, and

– causes disk-shaped red blood cells to deform into

a sickle shape with jagged edges.


Figure 9.UN04

Pleiotropy Multiple traits

(e.g., sickle-cell

disease)

Singlegene

Figure 9.21

Sickled cells can lead to a cascade

of symptoms, such as weakness,

pain, organ damage, and paralysis.

Abnormal hemoglobin crystallizesinto long flexible chains, causing

red blood cells to becomesickle-shaped.

Individual homozygous

for sickle-cell allele

Sickle-cell (abnormal) hemoglobin

Co

lori

ze

d S

EM

Polygenic Inheritance

• Polygenic inheritance is the additive effects of

two or more genes on a single phenotype.


Figure 9.UN05

Multiple genes

Polygenic

inheritance Single trait

(e.g., height)

Figure 9.22

F1 Generation

P Generation

F2 Generation Sperm

Eggs

Fra

cti

on

of

po

pu

lati

on

aabbcc

(very short)

AABBCC

(very tall)

AaBbCc

(medium height)

AaBbCc

(medium height)

short allele

tall allele

Very short Very tallAdult height

2064

1564

664

164

164

664

1564

2064

1564

664

164

18

18

18

18

18

18

18

18

18

18

18

18

18

18

18

18

Figure 9.22a

F1 Generation

P Generation

aabbcc

(very short)

AABBCC

(very tall)

AaBbCc

(medium height)

AaBbCc

(medium height)

short allele

tall allele

The Role of Environment

• Many human characters result from a combination

of

– heredity and

– environment.

• Only genetic influences are inherited.


Figure 9.23

THE CHROMOSOMAL BASIS OF INHERITANCE

• The chromosome theory of inheritance states

that

– genes are located at specific positions (loci) on

chromosomes and

– the behavior of chromosomes during meiosis and

fertilization accounts for inheritance patterns.


THE CHROMOSOMAL BASIS OF INHERITANCE

• It is chromosomes that

– undergo segregation and independent assortment

during meiosis and

– account for Mendel’s laws.


Figure 9.24

F1 Generation

P Generation

Gametes

Round-yellowseeds

(RRYY)

Wrinkled-greenseeds(rryy)

MEIOSIS

FERTILIZATION

MEIOSIS

All round-yellowseeds(RrYy)

Law of Segregation: Follow the long

chromosomes (carrying R and r) taking

either the left or right branch.

The R and r alleles segregate in

anaphase I of meiosis.

Only one long

chromosome ends

up in each gamete.

Gametes

Fertilization recombines the r

and R alleles at random.

F2 Generation9 : 3 : 3 : 1

FERTILIZATION AMONG THE F1 PLANTSFertilization results in the 9:3:3:1

phenotypic ratio in the F2 generation.

They sort independently,

giving four gamete types.

They are arranged in either of

two equally likely ways at

metaphase I.

Law of Independent Assortment:

Follow both the long and the short

chromosomes.

Metaphase I(alternative

arrangements)

Metaphase

II

Y

Y

Y

R R

R

y

y

y

r

r

r

r

r r

rr

r r r r

y

y y

yy

yy y y

RRRR

R R

R R

R

Y

Y Y

YY

Y Y Y Y

RY ry rY Ry4

1

4

1

4

1

4

1

Linked Genes

• Linked genes

– are located close together on a chromosome and

– tend to be inherited together.

• Thomas Hunt Morgan

– used the fruit fly Drosophila melanogaster and

– determined that some genes were linked based on

the inheritance patterns of their traits.


Figure 9.25-2

Dihybrid testcross

Results

Gray body,

long wings

(wild-type)

Black body,

short wings

(mutant)

Female Male

GgLl ggll

Offspring

Gray-long

GgLl

Black-short

ggll

Gray-short

GgllBlack-long

ggLl

965 944 206 185

Parental phenotypes 83% Recombinant phenotypes 17%

Genetic Recombination: Crossing Over

• Crossing over can

– separate linked alleles,

– produce gametes with recombinant gametes, and

– produce offspring with recombinant phenotypes.

• The percentage of recombinant offspring among

the total is called the recombination frequency.


Figure 9.26

Crossing overPair ofhomologouschromosomes

A

Recombinant gametes

B

A B

a b

a b

Parental gametes

A Bab

Figure 9.27

Parental gametes Recombinant gametesSperm

CROSSING OVER

Parental Recombinant

GgLl

(female)

ggll

(male)

Eggs

Offspring

FERTILIZATION

G L

g l

g l

g l

g lg LG lg lG L

G L

g l

g l

g l g l g l

G l g L

Linkage Maps

• Early studies of crossing over were performed

using the fruit fly Drosophila melanogaster.

• Alfred H. Sturtevant, a student of Morgan,

– developed a method for mapping the relative gene

locations,

– which resulted in the creation of linkage maps.


Figure 9.28

Chromosomeg c

Recombination

frequencies

l

17%

9.5%9%

SEX CHROMOSOMES AND SEX-LINKED GENES

• Sex chromosomes influence the inheritance of

certain traits. For example, humans that have a

pair of sex chromosomes designated

– X and Y are male or

– X and X are female.


Figure 9.29

Male Female

Sperm Egg

Offspring

Female Male

YX

44

XY

44

XX

22X

22Y

22X

44

XX

44

XY

Somatic

cells

Co

lori

zed

SE

M

Sex Determination in Humans

• Nearly all mammals have a pair of sex

chromosomes designated X and Y.

– Males have an X and Y.

– Females have XX.


Figure 9.UN06

Female

Somatic

cells

Male

44

XY

44

XX

Sex-Linked Genes

• Any gene located on a sex chromosome is called a

sex-linked gene.

– Most sex-linked genes are found on the X

chromosome.

– Red-green colorblindness is

– a common human sex-linked disorder and

– caused by a malfunction of light-sensitive cells in

the eyes.


Figure 9.UN07

Figure 9.30

Figure 9.31

Sperm

Colorblind individual

Sperm Sperm

Unaffected individual Carrier

(a) Normal female colorblind male (b) Carrier female normal male (c) Carrier female colorblind male

EggsEggsEggs

Key

XNXN XnY

Xn Y Y YXnXN

XNXn XNY XNXn XnY

Xn Xn

XNXN

XN

XN XNXn

XNXn

XNXN

XNXn

XNXn

XnXn

XNY

XnY

XNYXNY

XNY XnY

• Hemophilia

– is a sex-linked recessive blood-clotting trait that

may result in excessive bleeding and death after

relatively minor cuts and bruises and

– has plagued the royal families of Europe.

Sex-Linked Genes


Figure 9.32

AlbertQueen

Victoria

Alice Louis

Alexandra CzarNicholas IIof Russia

Alexis

Evolution Connection: Barking Up the Evolutionary Tree

• About 15,000 years ago in East Asia, people

began to cohabit with ancestral canines that were

predecessors of modern wolves and dogs.

• As people settled into geographically distinct

populations,

– different canines became separated and

– eventually became inbred.


• A 2010 study indicated that small dogs were

developed within the first permanent agricultural

settlements of the Middle East around 12,000

years ago.

• Continued over millennia, genetic tinkering has

resulted in a diverse array of dog body types and

behaviors.

Evolution Connection: Barking Up the Evolutionary Tree


Figure 9.33

Chinese shar-pei

Ancestralcanine

Wolf

Akita

Basenji

Siberian husky

Alaskanmalamute

Afghan hound

Rottweiler

Saluki

Sheepdog

Retriever

Chapter 9•Each of the characters Mendel studied occurred in two distinct traits. In an Abbey...

Documents

Transcript of Chapter 9•Each of the characters Mendel studied occurred in two distinct traits. In an Abbey...