Mendel and the Gene Idea

Слайд 1Chapter 14
Mendel and the Gene Idea

Слайд 2Overview: 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)

Слайд 3The “particulate” hypothesis is the idea that parents pass on discrete

heritable units (genes)
Mendel documented a particulate mechanism through his experiments with garden peas

Слайд 4Fig. 14-1

Слайд 5Concept 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

Слайд 6Mendel’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 of plants can be controlled
Each pea plant has sperm-producing organs (stamens) and egg-producing organs (carpels)
Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another

Слайд 7

Fig. 14-2
TECHNIQUE
RESULTS
Parental
generation
(P)
Stamens
Carpel
1
2
3
4
First
filial
gener-
ation
offspring
(F1)
5

Слайд 8

Fig. 14-2a
Stamens
Carpel
Parental
generation
(P)
TECHNIQUE
1
2
3
4

Слайд 9

Fig. 14-2b
First
filial
gener-
ation
offspring
(F1)
RESULTS
5

Слайд 10Mendel chose to track only those characters that varied in an

either-or manner
He also used varieties that were true-breeding (plants that produce offspring of the same variety when they self-pollinate)

Слайд 11In 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, the F2 generation is produced

Слайд 12The Law of Segregation
When Mendel crossed contrasting, true-breeding 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

Слайд 13
Fig. 14-3-1
EXPERIMENT
P Generation
(true-breeding
parents)
Purple
flowers
White
flowers
×

Слайд 14Fig. 14-3-2

EXPERIMENT
P Generation
(true-breeding
parents)
Purple
flowers
White
flowers
×
F1 Generation
(hybrids)
All plants had
purple

flowers

Слайд 15Fig. 14-3-3

EXPERIMENT
P Generation
(true-breeding
parents)
Purple
flowers
White
flowers
×
F1 Generation
(hybrids)
All plants had
purple

flowers

F2 Generation

705 purple-flowered
plants

224 white-flowered
plants

Слайд 16Mendel 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
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

Слайд 17Table 14-1

Слайд 18Mendel’s Model
Mendel developed a hypothesis to explain the 3:1 inheritance pattern

he observed in F2 offspring
Four related concepts make up this model
These concepts can be related to what we now know about genes and chromosomes

Слайд 19The first concept is that 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

Слайд 20Fig. 14-4
Allele for purple flowers
Homologous
pair of
chromosomes

Locus for flower-color gene
Allele for white

flowers

Слайд 21The second concept is that 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 locus on a chromosome 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

Слайд 22The third concept is that 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

Слайд 23The fourth concept, now known as the law of segregation, states

that 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 somatic cells of an organism
This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis

Слайд 24Mendel’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

Слайд 25
Fig. 14-5-1
P Generation
Appearance:
Genetic makeup:
Gametes:
Purple flowers
White flowers
PP
P
pp
p

Слайд 26

Fig. 14-5-2
P Generation
Appearance:
Genetic makeup:
Gametes:
Purple flowers
White flowers
PP
P
pp
p
F1 Generation
Gametes:
Genetic makeup:
Appearance:
Purple flowers
Pp
P
p
1/2
1/2

Слайд 27

Fig. 14-5-3
P Generation
Appearance:
Genetic makeup:
Gametes:
Purple flowers
White flowers
PP
P
pp
p
F1 Generation
Gametes:
Genetic makeup:
Appearance:
Purple flowers
Pp
P
p
1/2
1/2
F2 Generation
Sperm
Eggs
P
P
PP
Pp
p
p
Pp
pp
3
1

Слайд 28Useful 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

Слайд 29Because 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

Слайд 30Fig. 14-6
Phenotype
Purple
Purple
3
Purple
Genotype
1
White
Ratio 3:1

(homozygous)
(homozygous)
(heterozygous)
(heterozygous)
PP
Pp
Pp
pp
Ratio 1:2:1
1
1
2

Слайд 31The Testcross
How can we tell the genotype of an individual with

the dominant phenotype?
Such an individual must have one dominant allele, but the 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

Слайд 32

Fig. 14-7
TECHNIQUE
RESULTS
Dominant phenotype,
unknown genotype:
PP or Pp?
Predictions
Recessive phenotype,
known genotype:

pp

×

If PP

If Pp

or

Sperm

p

P

p

Eggs

Pp

pp

or

All offspring purple

1/2 offspring purple and
1/2 offspring white

Слайд 33
Fig. 14-7a
Dominant phenotype,
unknown genotype:
PP or Pp?
Predictions
Recessive phenotype,
known genotype:

pp

×

If PP

If Pp

or

Sperm

p

P

p

Eggs

Pp

pp

TECHNIQUE

Слайд 34
Fig. 14-7b
RESULTS
All offspring purple
or
1/2 offspring purple and
1/2 offspring white

Слайд 35The 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

Слайд 36Mendel 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

Слайд 37

Fig. 14-8
EXPERIMENT
RESULTS
P Generation
F1 Generation
Predictions
Gametes
Hypothesis of
dependent
assortment
YYRR
yyrr
YR
yr
YyRr
×
Hypothesis of
independent
assortment
or
Predicted
offspring of
F2 generation
Sperm
Sperm
YR
YR
yr
yr
Yr
YR
yR
Yr
yR
yr
YR
YYRR
YYRR
YyRr
YyRr
YyRr
YyRr
YyRr
YyRr
YYRr
YYRr
YyRR
YyRR
YYrr
Yyrr
Yyrr
yyRR
yyRr
yyRr
yyrr
yyrr
Phenotypic ratio 3:1
Eggs
Eggs
Phenotypic ratio

9:3:3:1

1/2

1/4

yr

1/4

3/4

9/16

3/16

1/16

Phenotypic ratio approximately 9:3:3:1

315

108

101

32

Слайд 38
Fig. 14-8a
EXPERIMENT
P Generation
F1 Generation
Predictions
Gametes
Hypothesis of
dependent
assortment
YYRR
yyrr
YR
yr
YyRr
×
Hypothesis of
independent
assortment
or
Predicted
offspring of
F2 generation
Sperm
Sperm
YR
YR
yr
yr
Yr
YR
yR
Yr
yR
yr
YR
YYRR
YYRR
YyRr
YyRr
YyRr
YyRr
YyRr
YyRr
YYRr
YYRr
YyRR
YyRR
YYrr
Yyrr
Yyrr
yyRR
yyRr
yyRr
yyrr
yyrr
Phenotypic ratio 3:1
Eggs
Eggs
Phenotypic ratio

9:3:3:1

1/2

1/4

yr

1/4

3/4

9/16

3/16

1/16

Слайд 39
Fig. 14-8b
RESULTS
Phenotypic ratio approximately 9:3:3:1
315
108
101
32

Слайд 40Using 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
Genes located near each other on the same chromosome tend to be inherited together

Слайд 41Concept 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

Слайд 42The 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 a coin: Each gamete has a chance of carrying the dominant allele and a chance of carrying the recessive allele

The Multiplication and Addition Rules Applied to Monohybrid Crosses

Слайд 43Fig. 14-9
Rr
Rr
×
Segregation of
alleles into eggs
Sperm
R
R
R
R
R
R
r
r
r
r
r
r
1/2
1/2
1/2
1/2
Segregation of
alleles into sperm
Eggs
1/4
1/4
1/4
1/4

Слайд 44The rule of addition 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

Слайд 45Solving 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 together

Слайд 46Fig. 14-UN1

Слайд 47Concept 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

Слайд 48Extending 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

Слайд 49Degrees 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

Слайд 50
Fig. 14-10-1
Red
P Generation
Gametes
White
CRCR
CWCW
CR
CW

Слайд 51

Fig. 14-10-2
Red
P Generation
Gametes
White
CRCR
CWCW
CR
CW
F1 Generation
Pink
CRCW
CR
CW
Gametes
1/2
1/2

Слайд 52

Fig. 14-10-3
Red
P Generation
Gametes
White
CRCR
CWCW
CR
CW
F1 Generation
Pink
CRCW
CR
CW
Gametes
1/2
1/2
F2 Generation
Sperm
Eggs
CR
CR
CW
CW
CRCR
CRCW
CRCW
CWCW
1/2
1/2
1/2
1/2

Слайд 53A dominant allele does not subdue a recessive allele; alleles don’t

interact
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

The Relation Between Dominance and
Phenotype

Слайд 54Tay-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

Слайд 55Frequency 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

Слайд 56The 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

Слайд 57Multiple 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

Слайд 58Fig. 14-11
IA
IB
i
A
B
none
(a) The three alleles for the ABO blood groups

and their associated carbohydrates

IAIA or IA i

A

B

IBIB or IB i

IAIB

AB

ii

O

(b) Blood group genotypes and phenotypes

Слайд 59Pleiotropy
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

Слайд 60Extending Mendelian Genetics for Two or More Genes
Some traits may be

determined by two or more genes

Слайд 61Epistasis
In epistasis, a gene at one locus alters the phenotypic expression

of a gene at a second locus
For example, in mice 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

Слайд 62Fig. 14-12
BbCc
BbCc
Sperm
Eggs
BC
bC
Bc
bc
BC
bC
Bc
bc
BBCC
1/4
1/4
1/4
1/4
1/4
1/4
1/4
1/4
BbCC
BBCc
BbCc
BbCC
bbCC
BbCc
bbCc
BBCc
BbCc
BbCc
bbCc
BBcc
Bbcc
Bbcc
bbcc
9
: 3
: 4
×

Слайд 63Polygenic 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

Слайд 64Fig. 14-13
Eggs
Sperm
Phenotypes:
Number of
dark-skin alleles:
0
1
2
3
4
5
6
1/64
6/64
15/64
20/64
15/64
6/64
1/64
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
AaBbCc
AaBbCc
×

Слайд 65Nature 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

Слайд 66Fig. 14-14

Слайд 67Norms of reaction are generally broadest for polygenic characters
Such characters are

called multifactorial because genetic and environmental factors collectively influence phenotype

Слайд 68Integrating 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

Слайд 69Concept 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

Слайд 70Pedigree 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

Слайд 71Fig. 14-15
Key
Male
Female
Affected
male
Affected
female
Mating
Offspring, in
birth order
(first-born on left)
1st generation
(grandparents)
2nd generation
(parents, aunts,
and uncles)
3rd generation
(two

sisters)

Ww

ww

Ww

ww

Ww

ww

Ww

WW

or

Widow’s peak

No widow’s peak

(a) Is a widow’s peak a dominant or recessive trait?

1st generation
(grandparents)

2nd generation
(parents, aunts,
and uncles)

3rd generation
(two sisters)

Ff

FF

or

ff

FF

or

Ff

Attached earlobe

Free earlobe

(b) Is an attached earlobe a dominant or recessive trait?

Слайд 72Fig. 14-15a
Key
Male
Female
Affected
male
Affected
female
Mating
Offspring, in
birth order
(first-born on left)

Слайд 73Fig. 14-15b
1st generation
(grandparents)
2nd generation
(parents, aunts,
and uncles)
3rd generation
(two sisters)
Widow’s peak
No widow’s peak
(a)

Is a widow’s peak a dominant or recessive trait?

Ww

ww

Ww

ww

Ww

ww

WW

Ww

or

Слайд 74Fig. 14-15c
Attached earlobe
1st generation
(grandparents)
2nd generation
(parents, aunts,
and uncles)
3rd generation
(two sisters)
Free earlobe
(b) Is

an attached earlobe a dominant or recessive trait?

Ff

ff

Ff

ff

FF

or

FF

Ff

Слайд 75Pedigrees 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

Слайд 76Recessively Inherited Disorders
Many genetic disorders are inherited in a recessive manner
Copyright

Слайд 77The 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 (i.e., pigmented)
Albinism is a recessive condition characterized by a lack of pigmentation in skin and hair

Слайд 78Fig. 14-16
Parents
Normal
Normal
Sperm
Eggs
Normal
Normal
(carrier)
Normal
(carrier)
Albino
Aa
Aa
A
A
AA
Aa
a
Aa
aa
a
×

Слайд 79If 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

Слайд 80Cystic 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
Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine

Слайд 81Sickle-Cell Disease
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
Symptoms include physical weakness, pain, organ damage, and even paralysis

Слайд 82Dominantly 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

Слайд 83Fig. 14-17
Eggs
Parents
Dwarf
Normal
Normal
Normal
Dwarf
Dwarf
Sperm
Dd
×
dd
d
D
Dd
dd
dd
Dd
d
d

Слайд 84Huntington’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

Huntington’s Disease

Слайд 85Multifactorial Disorders
Many diseases, such as heart disease and cancer, have both

genetic and environmental components
Little is understood about the genetic contribution to most multifactorial diseases

Слайд 86Genetic Testing and Counseling
Genetic counselors can provide information to prospective parents

concerned about a family history for a specific disease

Слайд 87Counseling Based on Mendelian Genetics and Probability Rules
Using family histories, genetic

counselors help couples determine the odds that their children will have genetic disorders

Слайд 88Tests for Identifying Carriers
For a growing number of diseases, tests are

available that identify carriers and help define the odds more accurately

Слайд 89Fetal 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

Слайд 90Fig. 14-18
Amniotic fluid
withdrawn
Fetus
Placenta
Uterus
Cervix
Centrifugation
Fluid
Fetal
cells
Several
hours
Several
weeks
Several
weeks
(a) Amniocentesis
(b) Chorionic villus sampling (CVS)
Several
hours
Several
hours
Fetal
cells
Bio-
chemical
tests
Karyotyping
Placenta
Chorionic
villi
Fetus
Suction tube
inserted
through
cervix

Слайд 91Fig. 14-18a
Fetus
Amniotic fluid
withdrawn
Placenta
Uterus
Cervix
Centrifugation
Fluid
Fetal
cells
Several
hours
Several
weeks
Several
weeks
Bio-
chemical
tests
Karyotyping
(a) Amniocentesis

Слайд 92Fig. 14-18b
(b) Chorionic villus sampling (CVS)
Bio-
chemical
tests
Placenta
Chorionic
villi
Fetus
Suction tube
inserted
through
cervix
Fetal
cells
Several
hours
Several
hours
Karyotyping

Слайд 93Newborn Screening
Some genetic disorders can be detected at birth by simple

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

Слайд 94Fig. 14-UN2
Degree of dominance
Complete dominance
of one allele
Incomplete dominance
of either allele
Codominance
Description
Heterozygous phenotype
same

as that of homo-
zygous dominant

Heterozygous phenotype
intermediate between
the two homozygous
phenotypes

Heterozygotes: Both
phenotypes expressed

Multiple alleles

Pleiotropy

In the whole population,
some genes have more
than two alleles

One gene is able to
affect multiple
phenotypic characters

CRCR

CRCW

CWCW

IAIB

IA , IB , i

ABO blood group alleles

Sickle-cell disease

PP

Pp

Example

Слайд 95Fig. 14-UN3
Description
Relationship among
genes
Epistasis
One gene affects
the expression of
another
Example
Polygenic
inheritance
A single phenotypic
character is
affected by
two

or more genes

BbCc

BC

bC

Bc

bc

9

: 3

: 4

AaBbCc

Слайд 96Fig. 14-UN4

Слайд 97Fig. 14-UN5
George
Sandra
Tom
Sam
Arlene
Wilma
Ann
Michael
Carla
Daniel
Alan
Tina
Christopher

Слайд 98Fig. 14-UN6

Слайд 99Fig. 14-UN7

Слайд 100Fig. 14-UN8

Слайд 101Fig. 14-UN9

Слайд 102Fig. 14-UN10

Слайд 103Fig. 14-UN11

Слайд 104You should now be able to:
Define the following terms: true breeding,

hybridization, monohybrid cross, P generation, F1 generation, F2 generation
Distinguish between the following pairs of terms: dominant and recessive; heterozygous and homozygous; genotype and phenotype
Use a Punnett square to predict the results of a cross and to state the phenotypic and genotypic ratios of the F2 generation

Слайд 105Explain how phenotypic expression in the heterozygote differs with complete dominance,

incomplete dominance, and codominance
Define and give examples of pleiotropy and epistasis
Explain why lethal dominant genes are much rarer than lethal recessive genes
Explain how carrier recognition, fetal testing, and newborn screening can be used in genetic screening and counseling

Mendel and the Gene Idea презентация

Содержание

Слайд 1Chapter 14Mendel and the Gene Idea

Слайд 2Overview: Drawing from the Deck of GenesWhat genetic principles account for

Слайд 3The “particulate” hypothesis is the idea that parents pass on discrete

Слайд 4Fig. 14-1

Слайд 5Concept 14.1: Mendel used the scientific approach to identify two laws

Слайд 6Mendel’s Experimental, Quantitative ApproachAdvantages of pea plants for genetic study:There are

Слайд 7Fig. 14-2TECHNIQUERESULTSParentalgeneration(P)StamensCarpel1234Firstfilialgener-ationoffspring(F1)5

Слайд 8Fig. 14-2aStamensCarpelParentalgeneration(P)TECHNIQUE1234

Слайд 9Fig. 14-2bFirstfilialgener-ationoffspring(F1)RESULTS5

Слайд 10Mendel chose to track only those characters that varied in an

Слайд 11In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a

Слайд 12The Law of SegregationWhen Mendel crossed contrasting, true-breeding white and purple

Слайд 13Fig. 14-3-1EXPERIMENTP Generation(true-breeding parents)Purpleflowers Whiteflowers×

Слайд 14Fig. 14-3-2EXPERIMENTP Generation(true-breeding parents)Purpleflowers Whiteflowers×F1 Generation (hybrids)All plants hadpurple

Слайд 15Fig. 14-3-3EXPERIMENTP Generation(true-breeding parents)Purpleflowers Whiteflowers×F1 Generation (hybrids)All plants hadpurple

Слайд 16Mendel reasoned that only the purple flower factor was affecting flower

Слайд 17Table 14-1

Слайд 18Mendel’s ModelMendel developed a hypothesis to explain the 3:1 inheritance pattern

Слайд 19The first concept is that alternative versions of genes account for

Слайд 20Fig. 14-4Allele for purple flowersHomologouspair ofchromosomesLocus for flower-color geneAllele for white

Слайд 21The second concept is that for each character an organism inherits

Слайд 22The third concept is that if the two alleles at a

Слайд 23The fourth concept, now known as the law of segregation, states

Слайд 24Mendel’s segregation model accounts for the 3:1 ratio he observed in

Слайд 25Fig. 14-5-1P GenerationAppearance:Genetic makeup:Gametes:Purple flowersWhite flowersPPPppp

Слайд 26Fig. 14-5-2P GenerationAppearance:Genetic makeup:Gametes:Purple flowersWhite flowersPPPpppF1 GenerationGametes:Genetic makeup:Appearance:Purple flowersPpPp1/21/2

Слайд 27Fig. 14-5-3P GenerationAppearance:Genetic makeup:Gametes:Purple flowersWhite flowersPPPpppF1 GenerationGametes:Genetic makeup:Appearance:Purple flowersPpPp1/21/2F2 GenerationSpermEggsPPPPPpppPppp31

Слайд 28Useful Genetic VocabularyAn organism with two identical alleles for a character

Слайд 29Because of the different effects of dominant and recessive alleles, an

Слайд 30Fig. 14-6PhenotypePurplePurple3PurpleGenotype1WhiteRatio 3:1(homozygous)(homozygous)(heterozygous)(heterozygous)PPPpPpppRatio 1:2:1112

Слайд 31The TestcrossHow can we tell the genotype of an individual with

Слайд 32Fig. 14-7TECHNIQUERESULTSDominant phenotype, unknown genotype:PP or Pp?PredictionsRecessive phenotype, known genotype:

Слайд 33Fig. 14-7aDominant phenotype, unknown genotype:PP or Pp?PredictionsRecessive phenotype, known genotype:

Слайд 34Fig. 14-7bRESULTSAll offspring purpleor1/2 offspring purple and1/2 offspring white

Слайд 35The Law of Independent AssortmentMendel derived the law of segregation by

Слайд 36Mendel identified his second law of inheritance by following two characters

Слайд 39Fig. 14-8bRESULTSPhenotypic ratio approximately 9:3:3:131510810132

Слайд 40Using a dihybrid cross, Mendel developed the law of independent assortmentThe

Слайд 41Concept 14.2: The laws of probability govern Mendelian inheritanceMendel’s laws of

Слайд 42The multiplication rule states that the probability that two or more

Слайд 43Fig. 14-9RrRr×Segregation ofalleles into eggsSpermRRRRRRrrrrrr1/21/21/21/2Segregation ofalleles into spermEggs1/41/41/41/4

Слайд 44The rule of addition states that the probability that any one

Слайд 45Solving Complex Genetics Problems with the Rules of ProbabilityWe can apply

Слайд 46Fig. 14-UN1

Слайд 47Concept 14.3: Inheritance patterns are often more complex than predicted by

Слайд 48Extending Mendelian Genetics for a Single GeneInheritance of characters by a

Слайд 49Degrees of Dominance Complete dominance occurs when phenotypes of the heterozygote

Слайд 50Fig. 14-10-1RedP GenerationGametesWhiteCRCRCWCWCRCW

Слайд 51Fig. 14-10-2RedP GenerationGametesWhiteCRCRCWCWCRCWF1 GenerationPinkCRCWCRCWGametes1/21/2

Слайд 52Fig. 14-10-3RedP GenerationGametesWhiteCRCRCWCWCRCWF1 GenerationPinkCRCWCRCWGametes1/21/2F2 GenerationSpermEggsCRCRCWCWCRCRCRCWCRCWCWCW1/21/21/21/2

Слайд 53A dominant allele does not subdue a recessive allele; alleles don’t

Слайд 54Tay-Sachs disease is fatal; a dysfunctional enzyme causes an accumulation of

Слайд 55Frequency of Dominant AllelesDominant alleles are not necessarily more common in

Слайд 56The allele for this unusual trait is dominant to the allele

Слайд 57Multiple AllelesMost genes exist in populations in more than two allelic

Слайд 58Fig. 14-11IAIBiABnone(a) The three alleles for the ABO blood groups

Слайд 59PleiotropyMost genes have multiple phenotypic effects, a property called pleiotropy For

Слайд 60Extending Mendelian Genetics for Two or More GenesSome traits may be

Слайд 61EpistasisIn epistasis, a gene at one locus alters the phenotypic expression

Слайд 62Fig. 14-12BbCcBbCcSpermEggsBCbCBcbcBCbCBcbcBBCC1/41/41/41/41/41/41/41/4BbCCBBCcBbCcBbCCbbCCBbCcbbCcBBCcBbCcBbCcbbCcBBccBbccBbccbbcc9: 3: 4×

Слайд 63Polygenic InheritanceQuantitative characters are those that vary in the population along

Слайд 64Fig. 14-13EggsSpermPhenotypes:Number ofdark-skin alleles:01234561/646/6415/6420/6415/646/641/641/81/81/81/81/81/81/81/81/81/81/81/81/81/81/81/8AaBbCcAaBbCc×

Слайд 65Nature and Nurture: The Environmental Impact on PhenotypeAnother departure from Mendelian

Слайд 66Fig. 14-14

Слайд 67Norms of reaction are generally broadest for polygenic charactersSuch characters are

Слайд 68Integrating a Mendelian View of Heredity and VariationAn organism’s phenotype includes

Слайд 69Concept 14.4: Many human traits follow Mendelian patterns of inheritanceHumans are

Слайд 70Pedigree AnalysisA pedigree is a family tree that describes the interrelationships

Слайд 71Fig. 14-15KeyMaleFemaleAffectedmaleAffectedfemaleMatingOffspring, inbirth order(first-born on left)1st generation(grandparents)2nd generation(parents, aunts,and uncles)3rd generation(two

Слайд 72Fig. 14-15aKeyMaleFemaleAffectedmaleAffectedfemaleMatingOffspring, inbirth order(first-born on left)

Слайд 73Fig. 14-15b1st generation(grandparents)2nd generation(parents, aunts,and uncles)3rd generation(two sisters)Widow’s peakNo widow’s peak(a)

Слайд 74Fig. 14-15cAttached earlobe1st generation(grandparents)2nd generation(parents, aunts,and uncles)3rd generation(two sisters)Free earlobe(b) Is

Слайд 75Pedigrees can also be used to make predictions about future offspringWe

Слайд 76Recessively Inherited DisordersMany genetic disorders are inherited in a recessive mannerCopyright

Слайд 77The Behavior of Recessive AllelesRecessively inherited disorders show up only in

Слайд 78Fig. 14-16ParentsNormalNormalSpermEggsNormalNormal(carrier)Normal(carrier)AlbinoAaAaAAAAAaaAaaaa×

Слайд 79If a recessive allele that causes a disease is rare, then

Слайд 80Cystic FibrosisCystic fibrosis is the most common lethal genetic disease in

Слайд 1Chapter 14
Mendel and the Gene Idea

Слайд 2Overview: Drawing from the Deck of Genes
What genetic principles account for

Слайд 6Mendel’s Experimental, Quantitative Approach
Advantages of pea plants for genetic study:
There are

Слайд 7

Fig. 14-2
TECHNIQUE
RESULTS
Parental
generation
(P)
Stamens
Carpel
1
2
3
4
First
filial
gener-
ation
offspring
(F1)
5

Слайд 8

Fig. 14-2a
Stamens
Carpel
Parental
generation
(P)
TECHNIQUE
1
2
3
4

Слайд 9

Fig. 14-2b
First
filial
gener-
ation
offspring
(F1)
RESULTS
5

Слайд 12The Law of Segregation
When Mendel crossed contrasting, true-breeding white and purple

Слайд 13
Fig. 14-3-1
EXPERIMENT
P Generation
(true-breeding
parents)
Purple
flowers
White
flowers
×

Слайд 14Fig. 14-3-2

EXPERIMENT
P Generation
(true-breeding
parents)
Purple
flowers
White
flowers
×
F1 Generation
(hybrids)
All plants had
purple

Слайд 15Fig. 14-3-3

EXPERIMENT
P Generation
(true-breeding
parents)
Purple
flowers
White
flowers
×
F1 Generation
(hybrids)
All plants had
purple

Слайд 18Mendel’s Model
Mendel developed a hypothesis to explain the 3:1 inheritance pattern

Слайд 20Fig. 14-4
Allele for purple flowers
Homologous
pair of
chromosomes

Locus for flower-color gene
Allele for white

Слайд 25
Fig. 14-5-1
P Generation
Appearance:
Genetic makeup:
Gametes:
Purple flowers
White flowers
PP
P
pp
p

Слайд 26

Fig. 14-5-2
P Generation
Appearance:
Genetic makeup:
Gametes:
Purple flowers
White flowers
PP
P
pp
p
F1 Generation
Gametes:
Genetic makeup:
Appearance:
Purple flowers
Pp
P
p
1/2
1/2

Слайд 27

Fig. 14-5-3
P Generation
Appearance:
Genetic makeup:
Gametes:
Purple flowers
White flowers
PP
P
pp
p
F1 Generation
Gametes:
Genetic makeup:
Appearance:
Purple flowers
Pp
P
p
1/2
1/2
F2 Generation
Sperm
Eggs
P
P
PP
Pp
p
p
Pp
pp
3
1

Слайд 28Useful Genetic Vocabulary
An organism with two identical alleles for a character

Слайд 30Fig. 14-6
Phenotype
Purple
Purple
3
Purple
Genotype
1
White
Ratio 3:1

(homozygous)
(homozygous)
(heterozygous)
(heterozygous)
PP
Pp
Pp
pp
Ratio 1:2:1
1
1
2

Слайд 31The Testcross
How can we tell the genotype of an individual with

Слайд 32

Fig. 14-7
TECHNIQUE
RESULTS
Dominant phenotype,
unknown genotype:
PP or Pp?
Predictions
Recessive phenotype,
known genotype:

Слайд 33
Fig. 14-7a
Dominant phenotype,
unknown genotype:
PP or Pp?
Predictions
Recessive phenotype,
known genotype:

Слайд 34
Fig. 14-7b
RESULTS
All offspring purple
or
1/2 offspring purple and
1/2 offspring white

Слайд 35The Law of Independent Assortment
Mendel derived the law of segregation by

Слайд 39
Fig. 14-8b
RESULTS
Phenotypic ratio approximately 9:3:3:1
315
108
101
32

Слайд 40Using a dihybrid cross, Mendel developed the law of independent assortment
The

Слайд 41Concept 14.2: The laws of probability govern Mendelian inheritance
Mendel’s laws of

Слайд 43Fig. 14-9
Rr
Rr
×
Segregation of
alleles into eggs
Sperm
R
R
R
R
R
R
r
r
r
r
r
r
1/2
1/2
1/2
1/2
Segregation of
alleles into sperm
Eggs
1/4
1/4
1/4
1/4

Слайд 45Solving Complex Genetics Problems with the Rules of Probability
We can apply

Слайд 48Extending Mendelian Genetics for a Single Gene
Inheritance of characters by a

Слайд 49Degrees of Dominance
Complete dominance occurs when phenotypes of the heterozygote

Слайд 50
Fig. 14-10-1
Red
P Generation
Gametes
White
CRCR
CWCW
CR
CW

Слайд 51

Fig. 14-10-2
Red
P Generation
Gametes
White
CRCR
CWCW
CR
CW
F1 Generation
Pink
CRCW
CR
CW
Gametes
1/2
1/2

Слайд 52

Fig. 14-10-3
Red
P Generation
Gametes
White
CRCR
CWCW
CR
CW
F1 Generation
Pink
CRCW
CR
CW
Gametes
1/2
1/2
F2 Generation
Sperm
Eggs
CR
CR
CW
CW
CRCR
CRCW
CRCW
CWCW
1/2
1/2
1/2
1/2

Слайд 55Frequency of Dominant Alleles
Dominant alleles are not necessarily more common in

Слайд 57Multiple Alleles
Most genes exist in populations in more than two allelic

Слайд 58Fig. 14-11
IA
IB
i
A
B
none
(a) The three alleles for the ABO blood groups

Слайд 59Pleiotropy
Most genes have multiple phenotypic effects, a property called pleiotropy
For

Слайд 60Extending Mendelian Genetics for Two or More Genes
Some traits may be

Слайд 61Epistasis
In epistasis, a gene at one locus alters the phenotypic expression

Слайд 62Fig. 14-12
BbCc
BbCc
Sperm
Eggs
BC
bC
Bc
bc
BC
bC
Bc
bc
BBCC
1/4
1/4
1/4
1/4
1/4
1/4
1/4
1/4
BbCC
BBCc
BbCc
BbCC
bbCC
BbCc
bbCc
BBCc
BbCc
BbCc
bbCc
BBcc
Bbcc
Bbcc
bbcc
9
: 3
: 4
×

Слайд 63Polygenic Inheritance
Quantitative characters are those that vary in the population along

Слайд 64Fig. 14-13
Eggs
Sperm
Phenotypes:
Number of
dark-skin alleles:
0
1
2
3
4
5
6
1/64
6/64
15/64
20/64
15/64
6/64
1/64
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
AaBbCc
AaBbCc
×

Слайд 65Nature and Nurture: The Environmental Impact on Phenotype
Another departure from Mendelian

Слайд 67Norms of reaction are generally broadest for polygenic characters
Such characters are

Слайд 68Integrating a Mendelian View of Heredity and Variation
An organism’s phenotype includes

Слайд 69Concept 14.4: Many human traits follow Mendelian patterns of inheritance
Humans are

Слайд 70Pedigree Analysis
A pedigree is a family tree that describes the interrelationships

Слайд 71Fig. 14-15
Key
Male
Female
Affected
male
Affected
female
Mating
Offspring, in
birth order
(first-born on left)
1st generation
(grandparents)
2nd generation
(parents, aunts,
and uncles)
3rd generation
(two

Слайд 72Fig. 14-15a
Key
Male
Female
Affected
male
Affected
female
Mating
Offspring, in
birth order
(first-born on left)

Слайд 73Fig. 14-15b
1st generation
(grandparents)
2nd generation
(parents, aunts,
and uncles)
3rd generation
(two sisters)
Widow’s peak
No widow’s peak
(a)

Слайд 74Fig. 14-15c
Attached earlobe
1st generation
(grandparents)
2nd generation
(parents, aunts,
and uncles)
3rd generation
(two sisters)
Free earlobe
(b) Is

Слайд 75Pedigrees can also be used to make predictions about future offspring
We

Слайд 76Recessively Inherited Disorders
Many genetic disorders are inherited in a recessive manner
Copyright

Слайд 77The Behavior of Recessive Alleles
Recessively inherited disorders show up only in

Слайд 78Fig. 14-16
Parents
Normal
Normal
Sperm
Eggs
Normal
Normal
(carrier)
Normal
(carrier)
Albino
Aa
Aa
A
A
AA
Aa
a
Aa
aa
a
×

Слайд 80Cystic Fibrosis
Cystic fibrosis is the most common lethal genetic disease in

Слайд 81Sickle-Cell Disease
Sickle-cell disease affects one out of 400 African-Americans
The disease is

Слайд 82Dominantly Inherited Disorders
Some human disorders are caused by dominant alleles
Dominant alleles

Слайд 83Fig. 14-17
Eggs
Parents
Dwarf
Normal
Normal
Normal
Dwarf
Dwarf
Sperm
Dd
×
dd
d
D
Dd
dd
dd
Dd
d
d

Слайд 84Huntington’s disease is a degenerative disease of the nervous system
The disease

Слайд 85Multifactorial Disorders
Many diseases, such as heart disease and cancer, have both

Слайд 86Genetic Testing and Counseling
Genetic counselors can provide information to prospective parents

Слайд 87Counseling Based on Mendelian Genetics and Probability Rules
Using family histories, genetic

Слайд 88Tests for Identifying Carriers
For a growing number of diseases, tests are

Слайд 89Fetal Testing
In amniocentesis, the liquid that bathes the fetus is removed

Слайд 91Fig. 14-18a
Fetus
Amniotic fluid
withdrawn
Placenta
Uterus
Cervix
Centrifugation
Fluid
Fetal
cells
Several
hours
Several
weeks
Several
weeks
Bio-
chemical
tests
Karyotyping
(a) Amniocentesis

Слайд 92Fig. 14-18b
(b) Chorionic villus sampling (CVS)
Bio-
chemical
tests
Placenta
Chorionic
villi
Fetus
Suction tube
inserted
through
cervix
Fetal
cells
Several
hours
Several
hours
Karyotyping

Слайд 93Newborn Screening
Some genetic disorders can be detected at birth by simple

Слайд 94Fig. 14-UN2
Degree of dominance
Complete dominance
of one allele
Incomplete dominance
of either allele
Codominance
Description
Heterozygous phenotype
same

Слайд 95Fig. 14-UN3
Description
Relationship among
genes
Epistasis
One gene affects
the expression of
another
Example
Polygenic
inheritance
A single phenotypic
character is
affected by
two

Слайд 97Fig. 14-UN5
George
Sandra
Tom
Sam
Arlene
Wilma
Ann
Michael
Carla
Daniel
Alan
Tina
Christopher

Слайд 104You should now be able to:
Define the following terms: true breeding,