LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserma...
Overview: Drawing from the Deck of Genes
• What genetic principles account for the passing
of traits from parents to offsp...
• The “particulate” hypothesis is the idea that
parents pass on discrete heritable units
(genes)
• This hypothesis can exp...
Figure 14.1
Concept 14.1: Mendel used the scientific
approach to identify two laws of inheritance
• Mendel discovered the basic princi...
Mendel’s Experimental, Quantitative
Approach
• Advantages of pea plants for genetic study
– There are many varieties with ...
Figure 14.2

TECHNIQUE
1

2
Parental
generation
(P)
3

Stamens
Carpel
4

RESULTS
First filial
generation
offspring
(F1)

5
Figure 14.2a

TECHNIQUE
1

2
Parental
generation
(P)

Stamens
3

Carpel
4
Figure 14.2b

RESULTS
First filial
generation
offspring
(F1)

5
• Mendel chose to track only those characters
that occurred in two distinct alternative forms
• He also used varieties tha...
• In a typical experiment, Mendel mated two
contrasting, true-breeding varieties, a process
called hybridization
• The tru...
The Law of Segregation
• When Mendel crossed contrasting, truebreeding white- and purple-flowered pea plants,
all of the F...
Figure 14.3-1

EXPERIMENT
P Generation
(true-breeding
parents)

Purple
flowers

White
flowers
Figure 14.3-2

EXPERIMENT
P Generation
(true-breeding
parents)

F1 Generation
(hybrids)

Purple
flowers

White
flowers

Al...
Figure 14.3-3

EXPERIMENT
P Generation
(true-breeding
parents)

Purple
flowers

White
flowers

F1 Generation
(hybrids)

Al...
• Mendel reasoned that only the purple flower
factor was affecting flower color in the F1 hybrids
• Mendel called the purp...
• Mendel observed the same pattern of
inheritance in six other pea plant characters,
each represented by two traits
• What...
Table 14.1
Mendel’s Model
• Mendel developed a hypothesis to explain the
3:1 inheritance pattern he observed in F 2
offspring
• Four ...
• First: alternative versions of genes account for
variations in inherited characters
• For example, the gene for flower c...
Figure 14.4

Allele for purple flowers

Locus for flower-color gene

Pair of
homologous
chromosomes

Allele for white flow...
• Second: for each character, an organism
inherits two alleles, one from each parent
• Mendel made this deduction without ...
• Third: if the two alleles at a locus differ, then one
(the dominant allele) determines the organism’s
appearance, and th...
• Fourth: (now known as the law of segregation):
the two alleles for a heritable character separate
(segregate) during gam...
• Mendel’s segregation model accounts for the 3:1
ratio he observed in the F2 generation of his
numerous crosses
• The pos...
Figure 14.5-1

P Generation
Appearance:
Purple flowers White flowers
Genetic makeup:
pp
PP
p
Gametes:
P
Figure 14.5-2

P Generation
Appearance:
Purple flowers White flowers
Genetic makeup:
pp
PP
p
Gametes:
P

F1 Generation
App...
Figure 14.5-3

P Generation
Appearance:
Purple flowers White flowers
Genetic makeup:
pp
PP
p
Gametes:
P

F1 Generation
App...
Useful Genetic Vocabulary
• An organism with two identical alleles for a
character is said to be homozygous for the
gene c...
• Because of the different effects of dominant and
recessive alleles, an organism’s traits do not
always reveal its geneti...
Figure 14.6

Genotype

Purple

3

Phenotype

PP
(homozygous)

Purple

Pp
(heterozygous)

1

2
Purple

1

Pp
(heterozygous)...
The Testcross
• How can we tell the genotype of an individual with
the dominant phenotype?
• Such an individual could be e...
Figure 14.7

TECHNIQUE

Dominant phenotype,
unknown genotype:
PP or Pp?
Predictions
If purple-flowered
parent is PP
Sperm
...
The Law of Independent Assortment
• Mendel derived the law of segregation by
following a single character
• The F1 offspri...
• Mendel identified his second law of inheritance by
following two characters at the same time
• Crossing two true-breedin...
Figure 14.8
EXPERIMENT
YYRR

P Generation

yyrr

Gametes YR

yr

F1 Generation

Predictions

YyRr
Hypothesis of
dependent ...
• Using a dihybrid cross, Mendel developed the
law of independent assortment
• The law of independent assortment states th...
Concept 14.2: The laws of probability govern
Mendelian inheritance
• Mendel’s laws of segregation and independent
assortme...
The Multiplication and Addition Rules
Applied to Monohybrid Crosses
• The multiplication rule states that the probability
...
Figure 14.9

×

Rr
Segregation of
alleles into eggs

Rr
Segregation of
alleles into sperm

Sperm
/2

1

R

/2

/4

Eggs

1...
• The addition rule states that the probability that
any one of two or more exclusive events will
occur is calculated by a...
Solving Complex Genetics Problems with the
Rules of Probability
• We can apply the multiplication and addition
rules to pr...
Figure 14.UN01

Probability of YYRR = 1/4 (probability of YY) × 1/4 (RR) = 1/16
Probability of YyRR = 1/2 (Yy)

× 1/4 (RR)...
Figure 14.UN02

ppyyRr
ppYyrr
Ppyyrr
PPyyrr
ppyyrr

/4 (probability of pp) × 1/2 (yy) × 1/2 (Rr)
1
/ 4 × 1 /2 × 1 /2
1
/2 ...
Concept 14.3: Inheritance patterns are often
more complex than predicted by simple
Mendelian genetics
• The relationship b...
Extending Mendelian Genetics for a Single
Gene
• Inheritance of characters by a single gene may
deviate from simple Mendel...
Degrees of Dominance
• Complete dominance occurs when phenotypes
of the heterozygote and dominant homozygote are
identical...
Figure 14.10-1

P Generation
White
CWCW

Red
CRCR
Gametes

CR

CW
Figure 14.10-2

P Generation
White
CWCW

Red
CRCR
Gametes

CR

CW

F1 Generation

Gametes 1/2 CR

Pink
CRCW
/2 CW

1
Figure 14.10-3

P Generation
White
CWCW

Red
CRCR
Gametes

CW

CR

F1 Generation

Pink
CRCW
/2 CW

Gametes 1/2 CR

1

Sper...
The Relation Between Dominance and
Phenotype
• A dominant allele does not subdue a recessive
allele; alleles don’t interac...
• Tay-Sachs disease is fatal; a dysfunctional
enzyme causes an accumulation of lipids in the
brain
– At the organismal lev...
Frequency of Dominant Alleles
• Dominant alleles are not necessarily more
common in populations than recessive alleles
• F...
• The allele for this unusual trait is dominant to the
allele for the more common trait of five digits per
appendage
• In ...
Multiple Alleles
• Most genes exist in populations in more than two
allelic forms
• For example, the four phenotypes of th...
Figure 14.11

(a) The three alleles for the ABO blood groups and their
carbohydrates
Allele
Carbohydrate

IA

IB

i
none

...
Pleiotropy
• Most genes have multiple phenotypic effects, a
property called pleiotropy
• For example, pleiotropic alleles ...
Extending Mendelian Genetics for Two or
More Genes
• Some traits may be determined by two or more
genes

© 2011 Pearson Ed...
Epistasis
• In epistasis, a gene at one locus alters the
phenotypic expression of a gene at a second
locus
• For example, ...
Figure 14.12

BbEe

Eggs
/4

/4

Be

/4

bE

/4

1

Be

/4

1

be

1

1

/4

bE

1

1

1

BE

/4

Sperm
1
/4 BE

BbEe

BBE...
Polygenic Inheritance
• Quantitative characters are those that vary in the
population along a continuum
• Quantitative var...
Figure 14.13

AaBbCc

AaBbCc
Sperm
1
/8 1/8
1
1

/8

1

/8

/8

/8

1

1

/64

15

1

/8

1

/8

/8

/8

1

/8

1

Eggs

1...
Nature and Nurture: The Environmental
Impact on Phenotype
• Another departure from Mendelian genetics
arises when the phen...
Figure 14.14
Figure 14.14a
Figure 14.14b
• Norms of reaction are generally broadest for
polygenic characters
• Such characters are called multifactorial
because ge...
Integrating a Mendelian View of Heredity
and Variation
• An organism’s phenotype includes its physical
appearance, interna...
Concept 14.4: Many human traits follow
Mendelian patterns of inheritance
• Humans are not good subjects for genetic
resear...
Pedigree Analysis
• A pedigree is a family tree that describes the
interrelationships of parents and children
across gener...
Figure 14.15

Key
Male

1st
generation

Affected
male

Female

Affected
female

Mating

1st
generation

Offspring

ww

ww
...
Figure 14.15a

Widow’s
peak
Figure 14.15b

No widow’s
peak
Figure 14.15c

Attached
earlobe
Figure 14.15d

Free
earlobe
• Pedigrees can also be used to make
predictions about future offspring
• We can use the multiplication and addition
rules...
Recessively Inherited Disorders
• Many genetic disorders are inherited in a
recessive manner
• These range from relatively...
The Behavior of Recessive Alleles
• Recessively inherited disorders show up only in
individuals homozygous for the allele
...
Figure 14.16

Parents
Normal
Aa

Normal
Aa

Sperm
A

a

A

AA
Normal

Aa
Normal
(carrier)

a

Aa
Normal
(carrier)

aa
Albi...
Figure 14.16a
• If a recessive allele that causes a disease is
rare, then the chance of two carriers meeting
and mating is low
• Consang...
Cystic Fibrosis
• Cystic fibrosis is the most common lethal
genetic disease in the United States,striking
one out of every...
Sickle-Cell Disease: A Genetic Disorder with
Evolutionary Implications
• Sickle-cell disease affects one out of 400
Africa...
Fig. 14-UN1

• Heterozygotes (said to have sickle-cell trait) are
usually healthy but may suffer some symptoms
• About one...
Dominantly Inherited Disorders
• Some human disorders are caused by
dominant alleles
• Dominant alleles that cause a letha...
Figure 14.17

Parents
Dwarf
Dd

Normal
dd

Sperm
D

d

d

Dd
Dwarf

dd
Normal

d

Dd
Dwarf

dd
Normal

Eggs
Figure 14.17a
Huntington’s Disease: A Late-Onset Lethal
Disease
• The timing of onset of a disease significantly
affects its inheritance...
Multifactorial Disorders
• Many diseases, such as heart disease,
diabetes, alcoholism, mental illnesses, and
cancer have b...
Genetic Testing and Counseling
• Genetic counselors can provide information to
prospective parents concerned about a famil...
Counseling Based on Mendelian Genetics
and Probability Rules
• Using family histories, genetic counselors help
couples det...
Tests for Identifying Carriers
• For a growing number of diseases, tests are
available that identify carriers and help def...
Figure 14.18
Fetal Testing
• In amniocentesis, the liquid that bathes the
fetus is removed and tested
• In chorionic villus sampling (C...
Figure 14.19

(a) Amniocentesis
1

(b) Chorionic villus sampling (CVS)
Ultrasound monitor
Amniotic
fluid
withdrawn

Ultras...
Newborn Screening
• Some genetic disorders can be detected at birth
by simple tests that are now routinely performed
in mo...
Figure 14.UN03

Relationship among
alleles of a single gene
Complete dominance
of one allele

Description
Heterozygous phe...
Figure 14.UN04

Relationship among
two or more genes
Epistasis

Description
The phenotypic
expression of one
gene affects ...
Figure 14.UN05

Character

Dominant

Recessive

Flower position

Axial (A)

Terminal (a)

Stem length

Tall (T)

Dwarf (t)...
Figure 14.UN06
Figure 14.UN07

George

Sandra

Tom

Sam

Arlene

Wilma

Ann

Michael
Carla

Daniel

Alan

Tina

Christopher
Figure 14.UN08
Figure 14.UN09
Figure 14.UN10
Figure 14.UN11
Figure 14.UN12
Figure 14.UN13
Figure 14.UN14
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  • Figure 14.1 What principles of inheritance did Gregor Mendel discover by breeding garden pea plants?
  • Figure 14.2 Research Method: Crossing Pea Plants
  • Figure 14.2 Research Method: Crossing Pea Plants
  • Figure 14.2 Research Method: Crossing Pea Plants
  • Figure 14.3 Inquiry: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?
  • Figure 14.3 Inquiry: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?
  • Figure 14.3 Inquiry: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?
  • Table 14.1 The Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants
  • Figure 14.4 Alleles, alternative versions of a gene.
  • Figure 14.5 Mendel’s law of segregation.
  • Figure 14.5 Mendel’s law of segregation.
  • Figure 14.5 Mendel’s law of segregation.
  • Figure 14.6 Phenotype versus genotype.
  • Figure 14.7 Research Method: The Testcross
  • Figure 14.8 Inquiry: Do the alleles for one character assort into gametes dependently or independently of the alleles for a different character?
  • Figure 14.9 Segregation of alleles and fertilization as chance events.
  • Figure 14.UN01 In-text figure, p. 270
  • Figure 14.UN02 In-text figure, p. 270
  • Figure 14.10 Incomplete dominance in snapdragon color.
  • Figure 14.10 Incomplete dominance in snapdragon color.
  • Figure 14.10 Incomplete dominance in snapdragon color.
  • Figure 14.11 Multiple alleles for the ABO blood groups.
  • Figure 14.12 An example of epistasis.
  • Figure 14.13 A simplified model for polygenic inheritance of skin color.
  • Figure 14.14 The effect of environment on phenotype.
  • Figure 14.14 The effect of environment on phenotype.
  • Figure 14.14 The effect of environment on phenotype.
  • Figure 14.15 Pedigree analysis.
  • Figure 14.15 Pedigree analysis.
  • Figure 14.15 Pedigree analysis.
  • Figure 14.15 Pedigree analysis.
  • Figure 14.15 Pedigree analysis.
  • Figure 14.16 Albinism: a recessive trait.
  • Figure 14.16 Albinism: a recessive trait.
  • Figure 14.17 Achondroplasia: a dominant trait.
  • Figure 14.17 Achondroplasia: a dominant trait.
  • Figure 14.18 Impact: Genetic Testing
  • Figure 14.19 Testing a fetus for genetic disorders.
  • Figure 14.UN03 Summary figure, Concept 14.3
  • Figure 14.UN04 Summary figure, Concept 14.3
  • Figure 14.UN05 Test Your Understanding, question 7
  • Figure 14.UN06 Test Your Understanding, question 14
  • Figure 14.UN07 Test Your Understanding, question 18
  • Figure 14.UN08 Appendix A: answer to Figure 14.8 legend question
  • Figure 14.UN09 Appendix A: answer to Figure 14.13 legend question
  • Figure 14.UN10 Appendix A: answer to Concept Check 14.1, question 1
  • Figure 14.UN11 Appendix A: answer to Concept Check 14.2, question 3
  • Figure 14.UN12 Appendix A: answer to Summary of Concept 14.2 Draw It question
  • Figure 14.UN13 Appendix A: answer to Test Your Understanding, question 2
  • Figure 14.UN14 Appendix A: answer to Test Your Understanding, question 6
  • 14 lecture presentation

    1. 1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 14 Mendel and the Gene Idea Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc.
    2. 2. Overview: Drawing from the Deck of Genes • What genetic principles account for the passing of traits from parents to offspring? • The “blending” hypothesis is the idea that genetic material from the two parents blends together (like blue and yellow paint blend to make green) © 2011 Pearson Education, Inc.
    3. 3. • The “particulate” hypothesis is the idea that parents pass on discrete heritable units (genes) • This hypothesis can explain the reappearance of traits after several generations • Mendel documented a particulate mechanism through his experiments with garden peas © 2011 Pearson Education, Inc.
    4. 4. Figure 14.1
    5. 5. Concept 14.1: Mendel used the scientific approach to identify two laws of inheritance • Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments © 2011 Pearson Education, Inc.
    6. 6. Mendel’s Experimental, Quantitative Approach • Advantages of pea plants for genetic study – There are many varieties with distinct heritable features, or characters (such as flower color); character variants (such as purple or white flowers) are called traits – Mating can be controlled – Each flower has sperm-producing organs (stamens) and egg-producing organ (carpel) – Cross-pollination (fertilization between different plants) involves dusting one plant with pollen from another © 2011 Pearson Education, Inc.
    7. 7. Figure 14.2 TECHNIQUE 1 2 Parental generation (P) 3 Stamens Carpel 4 RESULTS First filial generation offspring (F1) 5
    8. 8. Figure 14.2a TECHNIQUE 1 2 Parental generation (P) Stamens 3 Carpel 4
    9. 9. Figure 14.2b RESULTS First filial generation offspring (F1) 5
    10. 10. • Mendel chose to track only those characters that occurred in two distinct alternative forms • He also used varieties that were true-breeding (plants that produce offspring of the same variety when they self-pollinate) © 2011 Pearson Education, Inc.
    11. 11. • In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization • The true-breeding parents are the P generation • The hybrid offspring of the P generation are called the F1 generation • When F1 individuals self-pollinate or crosspollinate with other F1 hybrids, the F2 generation is produced © 2011 Pearson Education, Inc.
    12. 12. The Law of Segregation • When Mendel crossed contrasting, truebreeding white- and purple-flowered pea plants, all of the F1 hybrids were purple • When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white • Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation © 2011 Pearson Education, Inc.
    13. 13. Figure 14.3-1 EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers
    14. 14. Figure 14.3-2 EXPERIMENT P Generation (true-breeding parents) F1 Generation (hybrids) Purple flowers White flowers All plants had purple flowers Self- or cross-pollination
    15. 15. Figure 14.3-3 EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers Self- or cross-pollination F2 Generation 705 purpleflowered plants 224 white flowered plants
    16. 16. • Mendel reasoned that only the purple flower factor was affecting flower color in the F1 hybrids • Mendel called the purple flower color a dominant trait and the white flower color a recessive trait • The factor for white flowers was not diluted or destroyed because it reappeared in the F2 generation © 2011 Pearson Education, Inc.
    17. 17. • Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits • What Mendel called a “heritable factor” is what we now call a gene © 2011 Pearson Education, Inc.
    18. 18. Table 14.1
    19. 19. Mendel’s Model • Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F 2 offspring • Four related concepts make up this model • These concepts can be related to what we now know about genes and chromosomes © 2011 Pearson Education, Inc.
    20. 20. • First: alternative versions of genes account for variations in inherited characters • For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers • These alternative versions of a gene are now called alleles • Each gene resides at a specific locus on a specific chromosome © 2011 Pearson Education, Inc.
    21. 21. Figure 14.4 Allele for purple flowers Locus for flower-color gene Pair of homologous chromosomes Allele for white flowers
    22. 22. • Second: for each character, an organism inherits two alleles, one from each parent • Mendel made this deduction without knowing about the role of chromosomes • The two alleles at a particular locus may be identical, as in the true-breeding plants of Mendel’s P generation • Alternatively, the two alleles at a locus may differ, as in the F1 hybrids © 2011 Pearson Education, Inc.
    23. 23. • Third: if the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance • In the flower-color example, the F1 plants had purple flowers because the allele for that trait is dominant © 2011 Pearson Education, Inc.
    24. 24. • Fourth: (now known as the law of segregation): the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes • Thus, an egg or a sperm gets only one of the two alleles that are present in the organism • This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis © 2011 Pearson Education, Inc.
    25. 25. • Mendel’s segregation model accounts for the 3:1 ratio he observed in the F2 generation of his numerous crosses • The possible combinations of sperm and egg can be shown using a Punnett square, a diagram for predicting the results of a genetic cross between individuals of known genetic makeup • A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele © 2011 Pearson Education, Inc.
    26. 26. Figure 14.5-1 P Generation Appearance: Purple flowers White flowers Genetic makeup: pp PP p Gametes: P
    27. 27. Figure 14.5-2 P Generation Appearance: Purple flowers White flowers Genetic makeup: pp PP p Gametes: P F1 Generation Appearance: Genetic makeup: Gametes: Purple flowers Pp 1 1 /2 p /2 P
    28. 28. Figure 14.5-3 P Generation Appearance: Purple flowers White flowers Genetic makeup: pp PP p Gametes: P F1 Generation Appearance: Genetic makeup: Gametes: Purple flowers Pp 1 1 /2 p /2 P Sperm from F1 (Pp) plant F2 Generation Eggs from F1 (Pp) plant P p PP Pp Pp pp P p 3 :1
    29. 29. Useful Genetic Vocabulary • An organism with two identical alleles for a character is said to be homozygous for the gene controlling that character • An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that character • Unlike homozygotes, heterozygotes are not true-breeding © 2011 Pearson Education, Inc.
    30. 30. • Because of the different effects of dominant and recessive alleles, an organism’s traits do not always reveal its genetic composition • Therefore, we distinguish between an organism’s phenotype, or physical appearance, and its genotype, or genetic makeup • In the example of flower color in pea plants, PP and Pp plants have the same phenotype (purple) but different genotypes © 2011 Pearson Education, Inc.
    31. 31. Figure 14.6 Genotype Purple 3 Phenotype PP (homozygous) Purple Pp (heterozygous) 1 2 Purple 1 Pp (heterozygous) White pp (homozygous) Ratio 3:1 Ratio 1:2:1 1
    32. 32. The Testcross • How can we tell the genotype of an individual with the dominant phenotype? • Such an individual could be either homozygous dominant or heterozygous • The answer is to carry out a testcross: breeding the mystery individual with a homozygous recessive individual • If any offspring display the recessive phenotype, the mystery parent must be heterozygous © 2011 Pearson Education, Inc.
    33. 33. Figure 14.7 TECHNIQUE Dominant phenotype, unknown genotype: PP or Pp? Predictions If purple-flowered parent is PP Sperm p p Recessive phenotype, known genotype: pp P P Pp Eggs If purple-flowered parent is Pp Sperm p p or Pp Pp P Pp pp Eggs pp p Pp Pp RESULTS or All offspring purple /2 offspring purple and 1 /2 offspring white 1
    34. 34. The Law of Independent Assortment • Mendel derived the law of segregation by following a single character • The F1 offspring produced in this cross were monohybrids, individuals that are heterozygous for one character • A cross between such heterozygotes is called a monohybrid cross © 2011 Pearson Education, Inc.
    35. 35. • Mendel identified his second law of inheritance by following two characters at the same time • Crossing two true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters • A dihybrid cross, a cross between F1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independently © 2011 Pearson Education, Inc.
    36. 36. Figure 14.8 EXPERIMENT YYRR P Generation yyrr Gametes YR yr F1 Generation Predictions YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Sperm or Predicted offspring of F2 generation /4 YR 1 Sperm /2 yr /2 YR /4 Yr 1 1 /4 yR /4 yr 1 1 1 1 /4 YR YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr /2 YR 1 YyRr YYRR Eggs 1 /4 Yr Eggs /2 yr 1 YyRr /4 yyrr 1 /4 yR /4 3 1 1 Phenotypic ratio 3:1 /4 yr 9 /16 /16 3 3 /16 /16 1 Phenotypic ratio 9:3:3:1 RESULTS 315 108 101 32 Phenotypic ratio approximately 9:3:3:1
    37. 37. • Using a dihybrid cross, Mendel developed the law of independent assortment • The law of independent assortment states that each pair of alleles segregates independently of each other pair of alleles during gamete formation • Strictly speaking, this law applies only to genes on different, nonhomologous chromosomes or those far apart on the same chromosome • Genes located near each other on the same chromosome tend to be inherited together © 2011 Pearson Education, Inc.
    38. 38. Concept 14.2: The laws of probability govern Mendelian inheritance • Mendel’s laws of segregation and independent assortment reflect the rules of probability • When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss • In the same way, the alleles of one gene segregate into gametes independently of another gene’s alleles © 2011 Pearson Education, Inc.
    39. 39. The Multiplication and Addition Rules Applied to Monohybrid Crosses • The multiplication rule states that the probability that two or more independent events will occur together is the product of their individual probabilities • Probability in an F1 monohybrid cross can be determined using the multiplication rule • Segregation in a heterozygous plant is like flipping 1 a coin: Each gamete has a 2 chance of carrying 1 the dominant allele and a 2 chance of carrying the recessive allele © 2011 Pearson Education, Inc.
    40. 40. Figure 14.9 × Rr Segregation of alleles into eggs Rr Segregation of alleles into sperm Sperm /2 1 R /2 /4 Eggs 1 r /2 r R R 1 1 r R R 1 /2 1 /4 r r R r /4 1 /4 1
    41. 41. • The addition rule states that the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities • The rule of addition can be used to figure out the probability that an F2 plant from a monohybrid cross will be heterozygous rather than homozygous © 2011 Pearson Education, Inc.
    42. 42. Solving Complex Genetics Problems with the Rules of Probability • We can apply the multiplication and addition rules to predict the outcome of crosses involving multiple characters • A dihybrid or other multicharacter cross is equivalent to two or more independent monohybrid crosses occurring simultaneously • In calculating the chances for various genotypes, each character is considered separately, and then the individual probabilities are multiplied © 2011 Pearson Education, Inc.
    43. 43. Figure 14.UN01 Probability of YYRR = 1/4 (probability of YY) × 1/4 (RR) = 1/16 Probability of YyRR = 1/2 (Yy) × 1/4 (RR) = 1/8
    44. 44. Figure 14.UN02 ppyyRr ppYyrr Ppyyrr PPyyrr ppyyrr /4 (probability of pp) × 1/2 (yy) × 1/2 (Rr) 1 / 4 × 1 /2 × 1 /2 1 /2 × 1 /2 × 1 /2 1 /4 × 1 /2 × 1 /2 1 /4 × 1 /2 × 1 /2 1 Chance of at least two recessive traits = 1/16 = 1/16 = 2/16 = 1/16 = 1/16 = 6/16 or 3/8
    45. 45. Concept 14.3: Inheritance patterns are often more complex than predicted by simple Mendelian genetics • The relationship between genotype and phenotype is rarely as simple as in the pea plant characters Mendel studied • Many heritable characters are not determined by only one gene with two alleles • However, the basic principles of segregation and independent assortment apply even to more complex patterns of inheritance © 2011 Pearson Education, Inc.
    46. 46. Extending Mendelian Genetics for a Single Gene • Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations: – When alleles are not completely dominant or recessive – When a gene has more than two alleles – When a gene produces multiple phenotypes © 2011 Pearson Education, Inc.
    47. 47. Degrees of Dominance • Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical • In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties • In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways © 2011 Pearson Education, Inc.
    48. 48. Figure 14.10-1 P Generation White CWCW Red CRCR Gametes CR CW
    49. 49. Figure 14.10-2 P Generation White CWCW Red CRCR Gametes CR CW F1 Generation Gametes 1/2 CR Pink CRCW /2 CW 1
    50. 50. Figure 14.10-3 P Generation White CWCW Red CRCR Gametes CW CR F1 Generation Pink CRCW /2 CW Gametes 1/2 CR 1 Sperm F2 Generation /2 CR 1 /2 CW 1 /2 CR 1 CRCR CRCW Eggs /2 CW 1 CRCW CWCW
    51. 51. The Relation Between Dominance and Phenotype • A dominant allele does not subdue a recessive allele; alleles don’t interact that way • Alleles are simply variations in a gene’s nucleotide sequence • For any character, dominance/recessiveness relationships of alleles depend on the level at which we examine the phenotype © 2011 Pearson Education, Inc.
    52. 52. • Tay-Sachs disease is fatal; a dysfunctional enzyme causes an accumulation of lipids in the brain – At the organismal level, the allele is recessive – At the biochemical level, the phenotype (i.e., the enzyme activity level) is incompletely dominant – At the molecular level, the alleles are codominant © 2011 Pearson Education, Inc.
    53. 53. Frequency of Dominant Alleles • Dominant alleles are not necessarily more common in populations than recessive alleles • For example, one baby out of 400 in the United States is born with extra fingers or toes © 2011 Pearson Education, Inc.
    54. 54. • The allele for this unusual trait is dominant to the allele for the more common trait of five digits per appendage • In this example, the recessive allele is far more prevalent than the population’s dominant allele © 2011 Pearson Education, Inc.
    55. 55. Multiple Alleles • Most genes exist in populations in more than two allelic forms • For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: IA, IB, and i. • The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither © 2011 Pearson Education, Inc.
    56. 56. Figure 14.11 (a) The three alleles for the ABO blood groups and their carbohydrates Allele Carbohydrate IA IB i none B A (b) Blood group genotypes and phenotypes Genotype IAIA or IAi IBIB or IBi IAIB ii A B AB O Red blood cell appearance Phenotype (blood group)
    57. 57. Pleiotropy • Most genes have multiple phenotypic effects, a property called pleiotropy • For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease © 2011 Pearson Education, Inc.
    58. 58. Extending Mendelian Genetics for Two or More Genes • Some traits may be determined by two or more genes © 2011 Pearson Education, Inc.
    59. 59. Epistasis • In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus • For example, in Labrador retrievers and many other mammals, coat color depends on two genes • One gene determines the pigment color (with alleles B for black and b for brown) • The other gene (with alleles C for color and c for no color) determines whether the pigment will be deposited in the hair © 2011 Pearson Education, Inc.
    60. 60. Figure 14.12 BbEe Eggs /4 /4 Be /4 bE /4 1 Be /4 1 be 1 1 /4 bE 1 1 1 BE /4 Sperm 1 /4 BE BbEe BBEE BbEE BBEe BbEe BbEE bbEE BbEe bbEe BBEe BbEe BBee Bbee BbEe bbEe Bbee bbee 9 : 3 : 4 be
    61. 61. Polygenic Inheritance • Quantitative characters are those that vary in the population along a continuum • Quantitative variation usually indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype • Skin color in humans is an example of polygenic inheritance © 2011 Pearson Education, Inc.
    62. 62. Figure 14.13 AaBbCc AaBbCc Sperm 1 /8 1/8 1 1 /8 1 /8 /8 /8 1 1 /64 15 1 /8 1 /8 /8 /8 1 /8 1 Eggs 1 /8 1 /8 /8 1 1 /8 1 /8 Phenotypes: Number of dark-skin alleles: /64 1 0 6 /64 1 /64 15 2 20 3 /64 4 /64 6 5 1 /64 6
    63. 63. Nature and Nurture: The Environmental Impact on Phenotype • Another departure from Mendelian genetics arises when the phenotype for a character depends on environment as well as genotype • The norm of reaction is the phenotypic range of a genotype influenced by the environment • For example, hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity © 2011 Pearson Education, Inc.
    64. 64. Figure 14.14
    65. 65. Figure 14.14a
    66. 66. Figure 14.14b
    67. 67. • Norms of reaction are generally broadest for polygenic characters • Such characters are called multifactorial because genetic and environmental factors collectively influence phenotype © 2011 Pearson Education, Inc.
    68. 68. Integrating a Mendelian View of Heredity and Variation • An organism’s phenotype includes its physical appearance, internal anatomy, physiology, and behavior • An organism’s phenotype reflects its overall genotype and unique environmental history © 2011 Pearson Education, Inc.
    69. 69. Concept 14.4: Many human traits follow Mendelian patterns of inheritance • Humans are not good subjects for genetic research – Generation time is too long – Parents produce relatively few offspring – Breeding experiments are unacceptable • However, basic Mendelian genetics endures as the foundation of human genetics © 2011 Pearson Education, Inc.
    70. 70. Pedigree Analysis • A pedigree is a family tree that describes the interrelationships of parents and children across generations • Inheritance patterns of particular traits can be traced and described using pedigrees © 2011 Pearson Education, Inc.
    71. 71. Figure 14.15 Key Male 1st generation Affected male Female Affected female Mating 1st generation Offspring ww ww Ww 2nd generation Ww ww 3rd generation WW or Ww Widow’s peak ff ff (a) Is a widow’s peak a dominant or recessive trait? Ff Ff ff FF or Ff 3rd generation ww No widow’s peak Ff Ff 2nd generation FF or Ff Ww ww ww Ww ff ff Ww Ff Attached earlobe Free earlobe b) Is an attached earlobe a dominant or recessive trait?
    72. 72. Figure 14.15a Widow’s peak
    73. 73. Figure 14.15b No widow’s peak
    74. 74. Figure 14.15c Attached earlobe
    75. 75. Figure 14.15d Free earlobe
    76. 76. • Pedigrees can also be used to make predictions about future offspring • We can use the multiplication and addition rules to predict the probability of specific phenotypes © 2011 Pearson Education, Inc.
    77. 77. Recessively Inherited Disorders • Many genetic disorders are inherited in a recessive manner • These range from relatively mild to lifethreatening © 2011 Pearson Education, Inc.
    78. 78. The Behavior of Recessive Alleles • Recessively inherited disorders show up only in individuals homozygous for the allele • Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal; most individuals with recessive disorders are born to carrier parents • Albinism is a recessive condition characterized by a lack of pigmentation in skin and hair © 2011 Pearson Education, Inc.
    79. 79. Figure 14.16 Parents Normal Aa Normal Aa Sperm A a A AA Normal Aa Normal (carrier) a Aa Normal (carrier) aa Albino Eggs
    80. 80. Figure 14.16a
    81. 81. • If a recessive allele that causes a disease is rare, then the chance of two carriers meeting and mating is low • Consanguineous matings (i.e., matings between close relatives) increase the chance of mating between two carriers of the same rare allele • Most societies and cultures have laws or taboos against marriages between close relatives © 2011 Pearson Education, Inc.
    82. 82. Cystic Fibrosis • Cystic fibrosis is the most common lethal genetic disease in the United States,striking one out of every 2,500 people of European descent • The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes leading to a buildup of chloride ions outside the cell • Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine © 2011 Pearson Education, Inc.
    83. 83. Sickle-Cell Disease: A Genetic Disorder with Evolutionary Implications • Sickle-cell disease affects one out of 400 African-Americans • The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells • In homozygous individuals, all hemoglobin is abnormal (sickle-cell) • Symptoms include physical weakness, pain, organ damage, and even paralysis © 2011 Pearson Education, Inc.
    84. 84. Fig. 14-UN1 • Heterozygotes (said to have sickle-cell trait) are usually healthy but may suffer some symptoms • About one out of ten African Americans has sickle cell trait, an unusually high frequency of an allele with detrimental effects in homozygotes • Heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being heterozygous © 2011 Pearson Education, Inc.
    85. 85. Dominantly Inherited Disorders • Some human disorders are caused by dominant alleles • Dominant alleles that cause a lethal disease are rare and arise by mutation • Achondroplasia is a form of dwarfism caused by a rare dominant allele © 2011 Pearson Education, Inc.
    86. 86. Figure 14.17 Parents Dwarf Dd Normal dd Sperm D d d Dd Dwarf dd Normal d Dd Dwarf dd Normal Eggs
    87. 87. Figure 14.17a
    88. 88. Huntington’s Disease: A Late-Onset Lethal Disease • The timing of onset of a disease significantly affects its inheritance • Huntington’s disease is a degenerative disease of the nervous system • The disease has no obvious phenotypic effects until the individual is about 35 to 40 years of age • Once the deterioration of the nervous system begins the condition is irreversible and fatal © 2011 Pearson Education, Inc.
    89. 89. Multifactorial Disorders • Many diseases, such as heart disease, diabetes, alcoholism, mental illnesses, and cancer have both genetic and environmental components • Little is understood about the genetic contribution to most multifactorial diseases © 2011 Pearson Education, Inc.
    90. 90. Genetic Testing and Counseling • Genetic counselors can provide information to prospective parents concerned about a family history for a specific disease © 2011 Pearson Education, Inc.
    91. 91. Counseling Based on Mendelian Genetics and Probability Rules • Using family histories, genetic counselors help couples determine the odds that their children will have genetic disorders • Probabilities are predicted on the most accurate information at the time; predicted probabilities may change as new information is available © 2011 Pearson Education, Inc.
    92. 92. Tests for Identifying Carriers • For a growing number of diseases, tests are available that identify carriers and help define the odds more accurately © 2011 Pearson Education, Inc.
    93. 93. Figure 14.18
    94. 94. Fetal Testing • In amniocentesis, the liquid that bathes the fetus is removed and tested • In chorionic villus sampling (CVS), a sample of the placenta is removed and tested • Other techniques, such as ultrasound and fetoscopy, allow fetal health to be assessed visually in utero Video: Ultrasound of Human Fetus I © 2011 Pearson Education, Inc.
    95. 95. Figure 14.19 (a) Amniocentesis 1 (b) Chorionic villus sampling (CVS) Ultrasound monitor Amniotic fluid withdrawn Ultrasound monitor Fetus 1 Placenta Chorionic villi Fetus Placenta Uterus Cervix Cervix Uterus Centrifugation Fluid Fetal cells Several hours 2 Several weeks Biochemical and genetic tests Several hours Fetal cells 2 Several hours Several weeks 3 Karyotyping Suction tube inserted through cervix
    96. 96. 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 © 2011 Pearson Education, Inc.
    97. 97. Figure 14.UN03 Relationship among alleles of a single gene Complete dominance of one allele Description Heterozygous phenotype same as that of homozygous dominant Incomplete dominance Heterozygous phenotype intermediate between of either allele the two homozygous phenotypes Codominance Both phenotypes expressed in heterozygotes Example PP Pp CRCR CRCW CWCW IAIB Multiple alleles In the whole population, ABO blood group alleles some genes have more IA, IB, i than two alleles Pleiotropy One gene is able to affect Sickle-cell disease multiple phenotypic characters
    98. 98. Figure 14.UN04 Relationship among two or more genes Epistasis Description The phenotypic expression of one gene affects that of another Example BbEe BE BbEe bE Be be BE bE Be be 9 Polygenic inheritance A single phenotypic character is affected by two or more genes AaBbCc :3 :4 AaBbCc
    99. 99. Figure 14.UN05 Character Dominant Recessive Flower position Axial (A) Terminal (a) Stem length Tall (T) Dwarf (t) Seed shape Round (R) Wrinkled (r)
    100. 100. Figure 14.UN06
    101. 101. Figure 14.UN07 George Sandra Tom Sam Arlene Wilma Ann Michael Carla Daniel Alan Tina Christopher
    102. 102. Figure 14.UN08
    103. 103. Figure 14.UN09
    104. 104. Figure 14.UN10
    105. 105. Figure 14.UN11
    106. 106. Figure 14.UN12
    107. 107. Figure 14.UN13
    108. 108. Figure 14.UN14
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