Chapter 11 ppt

(1)

Biology

Sylvia S. Mader Michael Windelspecht

Chapter 11 Mendelian

Patterns of

Inheritance

Lecture Outline

See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into

PowerPoint without notes.

(2)

2

Outline

• 11.1 Gregor Mendel

• 11.2 Mendel’s Laws

(3)

11.1 Gregor Mendel

• Concept of Blending Inheritance:



Parents of contrasting appearance produce

offspring of intermediate appearance



Popular concept during Mendel’s time

• Mendel’s findings were in contrast with this



He formulated the Particulate Theory of

Inheritance

• Inheritance involves reshuffling of genes from generation to generation

(4)

Gregor Mendel

• Austrian monk

 Studied science and mathematics at the University of

Vienna

 Conducted breeding experiments with the garden pea

Pisum sativum

 Carefully gathered and documented mathematical

data from his experiments

• Formulated fundamental laws of heredity in the

early 1860s

 Had no knowledge of cells or chromosomes

 Did not have a microscope

(5)

Gregor Mendel

5

(6)

6

Gregor Mendel

• The garden pea:



Organism used in Mendel’s experiments



A good choice for several reasons:

• Easy to cultivate • Short generation

• Normally self-pollinating, but can be cross-pollinated by hand

(7)

Garden Pea Anatomy

7

stamen anther

a.

Flower Structure

filament

stigma

style

ovules in ovary

carpel

(8)

8

All peas are yellow when one parent produces yellow seeds and the other parent produces green seeds.

Brushing on pollen from another plant

Cutting away anthers

Garden Pea Anatomy

(9)

Garden Pea Anatomy

Trait _*Dominant Characteristics _*Recessive

Stem length

Pod shape

Seed shape

Seed color

Flower position

Flower color

Pod color

b.

Green Purple Axial Yellow Round Inflated

Tall Short

Constricted

Wrinkled

Green

Terminal

White

Yellow

(10)

11.2 Mendel’s Laws

• Mendel performed cross-breeding

experiments



Used “true-breeding” (homozygous) plants



Chose varieties that differed in only one trait

(

monohybrid cross

)



Performed reciprocal crosses

• Parental generation = P

• First filial generation offspring = F₁

• Second filial generation offspring = F₂

(11)

Monohybrid Cross done by Mendel

11

TT tt

Phenotypic Ratio

short 1

tall 3

Allele Key T = tall plant

(12)

Monohybrid Cross done by Mendel

12

P generation

TT tt

short 1

tall 3

t = short plant

(13)

Monohybrid Cross done by Mendel

13

P generation

TT tt

t T

P gametes Phenotypic Ratio

short 1

tall 3

(14)

Monohybrid Cross done by Mendel

14

tt P generation

TT tt

t T

Tt P gametes

F₁ generation Phenotypic Ratio

short 1

tall 3

(15)

Monohybrid Cross done by Mendel

15

eggs

s

per

m

P generation

T t

T

t

TT tt

t T

Tt P gametes

F1 gametes F1 generation Phenotypic Ratio

short 1

tall 3

Allele Key T = tall plant

(16)

Monohybrid Cross done by Mendel

eggs

spe

rm

P generation

T t

T

t

TT tt

t T

Tt

TT P gametes

F1 gametes

F₁ generation Phenotypic Ratio

short 1

tall 3

Allele Key T ₌tall plant

(17)

Monohybrid Cross done by Mendel

17

eggs

s

per

m

T t

T

t

TT tt

t T

Tt

TT Tt

F₁gametes Phenotypic Ratio

short 1

tall 3

Allele key

F₁generation P gametes F₁generation

(18)

Monohybrid Cross done by Mendel

18

eggs

s

per

m

P generation

T t

T

t

TT tt

t T

Tt

TT Tt

Tt P gametes

F1 gametes

F1 generation

short 1

tall 3

Allele Key T = tall plant

(19)

Monohybrid Cross done by Mendel

19

eggs

sp

erm

Offspring P generation

T t

T

t

TT tt

t T

Tt

TT Tt

Tt tt

P gametes

F₁ gametes

F₂ generation

F₁ generation

short 1

tall 3

Allele Key

T = tall plant

(20)

Mendel’s Laws

• Law of Segregation:

 Each individual has a pair of factors (alleles) for each

trait

 The factors (alleles) segregate (separate) during

gamete (sperm & egg) formation

 Each gamete contains only one factor (allele) from

each pair of factors

 Fertilization gives the offspring two factors for each

trait

(21)

Mendel’s Laws

• Classical Genetics and Mendel’s Cross:

 Each trait in a pea plant is controlled by two alleles

(alternate forms of a gene)

 Dominant allele (capital letter) masks the expression

of the recessive allele (lower-case)

 Alleles occur on a homologous pair of chromosomes

at a particular gene locus

• Homozygous = identical alleles

• Heterozygous = different alleles

(22)

Classical View of

Homologous Chromosomes

22 Replication

alleles at a gene locus

sister chromatids

b. Sister chromatids of duplicated chromosomes have same alleles for each gene. a. Homologous

chromosomes have alleles for same genes at specific loci. G R S t G R S t G R S t g r s T g r s T g r s T

(23)

Relationship Between Observed

Phenotype and F

₂

Offspring

Trait Stem length Pod shape Seed shape Seed color Flower position Flower color Pod color Dominant Characteristics Recessive Tall Inflated Round Yellow Axial Purple Green Short Constricted Wrinkled Green Terminal White Yellow Dominant

F2Results

Ratio Recessive Totals: 2.84:1 277 787

882 299 2.95:1

2.96:1 3.01:1 3.14:1 3.15:1 2.82:1 2.98:1 2,001 1,850 5,474 6,022 651 705 428 14,949 207 224 152 5,010

(24)

Mendel’s Laws

• Genotype

 Refers to the two alleles an individual has for a

specific trait

 If identical, genotype is homozygous

 If different, genotype is heterozygous

• Phenotype

 Refers to the physical appearance of the individual

(25)

Mendel’s Laws

• A dihybrid cross uses true-breeding plants differing in two traits • Mendel tracked each trait through two generations.

 Started with true-breeding plants differing in two traits

 The F₁ plants showed both dominant characteristics

 F₁ plants self-pollinated

 Observed phenotypes among F₂ plants

• Mendel formulated the Law of Independent Assortment

 The pair of factors for one trait segregate independently of the factors for other traits

 All possible combinations of factors can occur in the gametes

• P generation is the parental generation in a breeding experiment.

• F₁generation is the first-generation offspring in a breeding

experiment.

• F₂ generation is the second-generation offspring in a breeding

experiment

(26)

Dihybrid Cross Done by Mendel

× = = = T t G 9 3 3 ttgg TTGG P generation P gametes

F1 generation

F1 gametes

F2 generation

s p e rm eggs TtGg

TG tg

tg tG Tg TG TG TtGg Tg tG tg

TTGG TTGg TtGG

Ttgg TtGg TTgg TTGg ttGg ttGG TtGg TtGG ttgg ttGg Ttgg TtGg Allele Key Offspring Phenotypic Ratio green pod short plant

(27)

Independent Assortment and

Segregation during Meiosis

27

A _a

B

b

(28)

Independent Assortment and

Segregation during Meiosis

28

A

A A

a

a a

B

B B

b

b b

(29)

Independent Assortment and

Segregation during Meiosis

29

A

A A

a

a a

B

B B

b

b b

A A

b bB B a a Parent cell has two

pairs of homologous chromosomes.

(30)

Independent Assortment and

Segregation during Meiosis

30

A

A A

a

a a

B

B B

b

b b

A A

b bB B

a a

Parent cell has two pairs of homologous chromosomes.

All orientations of ho- mologous chromosomes are possible at meta- phase I in keeping with the law of independent

(31)

Independent Assortment and

Segregation during Meiosis

31 A A A A A a a a a a B B B B B b b b A A

b bB B

a a

b b

All orientations of ho- mologous chromosomes are possible at metaphase I in keeping with the law of independent assortment.

(32)

Independent Assortment and

Segregation during Meiosis

32 A A A A A a a a a a A A a a B B B B B B B b b b A A

b bB B

a a

b b

All orientations of ho- mologous chromosomes are possible at metaphase I in keeping with

the law of independent

(33)

Independent Assortment and

Segregation during Meiosis

33 A A A A A a a a a a A A a a B B B B B B B b b b A A b bB B

a a

b b

All orientations of ho- mologous chromosomes are possible at meta- phase I in keeping with the law of independent assortment.

At metaphase II, each daughter cell has only one member of each homologous pair in keeping with the law of segregation

(34)

Independent Assortment and

Segregation during Meiosis

34

All possible combi - tions of chromosomes and alleles occur in the gametes as suggested by Mendel's All orientations of ho-

mologous chromosomes are possible at

metaphase I in keeping with the law of

At metaphase II, each daughter cell has only one member of each homologous pair in keeping with the law of A

A A

A A AB ab Ab aB a a a a a a a A A b A a

a a

B B B B B B B B B B a B b

b b

A A

b b B B a a

b b b b b A b b

(35)

Mendel’s Laws

• Punnett Square



Table listing all possible genotypes resulting

from a cross

• All possible sperm genotypes are lined up on one side

• All possible egg genotypes are lined up on the other side

• Every possible zygote genotypes are placed within

(36)

Mendel’s Laws

• Punnett Square

 Allows us to easily calculate probability, of genotypes

and phenotypes among the offspring

 Punnett square in next slide shows a 50% (or ½)

chance

• The chance of E = ½

• The chance of e = ½

 An offspring will inherit:

• The chance of EE =½  ½=¼

• The chance of Ee =½  ½=¼

• The chance of eE =½  ½=¼

• The chance of ee =½  ½=¼

(37)

Punnett Square

37

eggs

spem

Punnett

square

Offspring Parents

E e

E

e

Ee

Ee EE

Ee Ee

Allele key Phenotypic Ratio unattached earlobes 3

1 E =

e =

unattached earlobes

attached earlobes attached earlobes

(38)

Mendel’s Laws

• Testcrosses

 Individuals with recessive phenotype always have the

homozygous recessive genotype

 However, individuals with dominant phenotype have

indeterminate genotype

• May be homozygous dominant, or

• Heterozygous

 A testcross determines the genotype of an individual

having the dominant phenotype

(39)

One-Trait Testcross

(40)

One-Trait Testcross

40

b.

t T

Tt Offspring

eggs sperm

TT tt

Allele Key

(41)

41

Mendel’s Laws

• Two-trait testcross:



An individual with both dominant phenotypes is

crossed with an individual with both recessive

phenotypes.



If the individual with the dominant phenotypes

(42)

Mendel’s Laws

• Genetic disorders are medical conditions caused by alleles inherited from parents

• Autosome - Any chromosome other than a sex chromosome (X or Y)

• Genetic disorders caused by genes on autosomes are called autosomal disorders

 Some genetic disorders are autosomal dominant

• An individual with AA has the disorder • An individual with Aa has the disorder

• An individual with aa does NOT have the disorder

 Other genetic disorders are autosomal recessive

• An individual with AA does NOT have the disorder

• An individual with Aa does NOT have the disorder, but is a carrier • An individual with aa DOES have the disorder

(43)

Autosomal Recessive Pedigree

43

I II III IV Key Gen er ati o n s

Autosomal recessive disorders

• Most affected children have unaffected parents.

• Heterozygotes (Aa) have an unaffected phenotype.

• Two affected parents will always have affected children. • Close relatives who reproduce are more likely to have affected children.

• Both males and females are affected with equal frequency. A? aa A?

A? Aa Aa A?

Aa *

Aa A?

A? aa

aa

aa = affected

Aa = carrier (unaffected) AA = unaffected

A? = unaffected

(44)

Autosomal Dominant Pedigree

44

• Affected children will usually have an affected parent.

• Heterozygotes (Aa) are affected.

• Two affected parents can produce an unaffected child. • Two unaffected parents will not have affected children. • Both males and females are affected with equal frequency.

AA = affected Aa = affected A? = affected

(one allele unknown) aa = unaffected

I

II

III Aa

aa Aa Aa * Aa A? aa

aa aa aa

aa aa aa Aa Key G eneration s

(45)

Mendel’s Laws

• Autosomal Recessive Disorders:



Methemoglobinemia

• Relatively harmless disorder

• Accumulation of methemoglobin in the blood causes skin to appear bluish-purple



Cystic Fibrosis

• Mucus in bronchial tubes and pancreatic ducts is particularly thick and viscous

(46)

Methemoglobinemia

46

(47)

Cystic Fibrosis

47

Cl-

H₂O

H₂O Cl-

Cl-

thick mucus defective

channel

nebulizer

percussion vest

(48)

Mendel’s Laws

• Autosomal Dominant Disorders



Osteogenesis Imperfecta

• Weakened, brittle bones

• Most cases are caused by mutation in genes required for the synthesis of type I collagen



Hereditary Spherocytosis

• Caused by a mutation in the ankyrin-1 gene

• Red blood cells become spherical, are fragile, and burst easily

(49)

11.3 Extending the Range of

Mendelian Genetics

• Some traits are controlled by multiple alleles (multiple

allelic traits)

• The gene exists in several allelic forms (but each individual only has two alleles)

• ABO blood types

 The alleles:

• IA = A antigen on red blood cells, anti-B antibody in plasma

• IB_{= B antigen on red blood cells, anti-A antibody in plasma}

• i = Neither A nor B antigens on red blood cells, both A and anti-B antibodies in plasma

• The ABO blood type is also an example of codominance

 More than one allele is fully expressed

 Both IA_and_IB_{are expressed in the presence of the other}

(50)

ABO Blood Type

50

Genotype

I

A

I

A

, I

A

i

I

B

I

B

, I

B

i

I

A

I

B

ii

Phenotype

A

B

(51)

Extending the Range of

Mendelian Genetics

• Incomplete Dominance

:

 Heterozygote has a phenotype intermediate between

that of either homozygote

• Homozygous red has red phenotype

• Homozygous white has white phenotype

• Heterozygote has pink (intermediate) phenotype

 Phenotype reveals genotype without a test cross

(52)

Incomplete Dominance

52

R1 R2

R1

R2

R₁R₂

R₁R₂ R₁R₁

R₂R₂

R1R2 R1R2

eggs

s

p

e

rm

Offspring

Key 1 R1R1

2 R1R2

1 R2R2

(53)

53

Extending the Range of

Mendelian Genetics

• Human examples of incomplete dominance:

 Familial Hypercholesterolemia (FH)

• Homozygotes for the mutant allele develop fatty deposits in the skin and tendons and may have heart attacks during childhood

• Heterozygotes may suffer heart attacks during early adulthood

(54)

54

Extending the Range of

Mendelian Genetics

• Human examples of incomplete dominance:



Incomplete penetrance

• The dominant allele may not always lead to the dominant phenotype in a heterozygote

• Many dominant alleles exhibit varying degrees of penetrance

• Example: polydactyly

– Extra digits on hands, feet, or both

(55)

Extending the Range of

Mendelian Genetics

• Pleiotropy

occurs when a single mutant

gene affects two or more distinct and

seemingly unrelated traits.

• Marfan syndrome is pleiotropic and results

in the following phenotypes:



disproportionately long arms, legs, hands, and

feet



a weakened aorta



poor eyesight

(56)

Marfan Syndrome

Chest wall deformities Long, thin fingers, arms, legs Scoliosis (curvature of the spine) Flat feet

Long, narrow face Loose joints

Skeleton Eyes Lungs Skin

Lens dislocation

Severe nearsightedness Collapsed lungs Stretch marks in skin _{Recurrent hernias} Dural ectasia: stretching of the membrane that holds spinal fluid Mitral valve

prolapse

Enlargement of aorta Heart and blood vessels

Aneurysm Aortic wall tear

Connective tissue defects

(57)

Extending the Range of

Mendelian Genetics

• Polygenic Inheritance:

 Occurs when a trait is governed by two or more

genes having different alleles

 Each dominant allele has a quantitative effect on the

phenotype

 These effects are additive

 Results in continuous variation of phenotypes within a

population

 The traits may also be affected by the environment

 Examples

• Human skin color • Height

(58)

Polygenic Inheritance

58

20 _— 64

15 _— 64

6 — 64

1 64

P

roport

ion

of

P

opula

tion

F₂generation

—

F1 generation

(59)

Extending the Range of

Mendelian Genetics

• X-Linked Inheritance



In mammals

• The X and Y chromosomes determine

gender

• Females are XX

• Males are XY

(60)

Extending the Range of

Mendelian Genetics

• X-Linked Inheritance



The term

X-linked

is used for genes that have

nothing to do with gender

• X-linked genes are carried on the X chromosome. • The Y chromosome does not carry these genes • Discovered in the early 1900s by a group at

Columbia University, headed by Thomas Hunt Morgan.

– Performed experiments with fruit flies

» They can be easily and inexpensively raised in simple laboratory glassware

» Fruit flies have the same sex chromosome pattern as humans

(61)

X

– Linked Inheritance

61

Xr_Y

XR_Y

XR

Xr

Y

Xr_Y

Xr _Y _XR

Offspring eggs s per m P generation P gametes

F2 generation

F₁generation

F₁gametes

Allele Key = = XR Xr red eyes white eyes Phenotypic Ratio all red-eyed red-eyed white-eyed females:

males: 1 1 XR_Y

XR_Xr

XR_XR

XR

XR_Xr

(62)

(63)

Extending the Range of

Mendelian Genetics

• Several X-linked recessive disorders occur in humans:

 Color blindness

• The allele for the blue-sensitive protein is autosomal

• The alleles for the red- and green-sensitive pigments are on the X chromosome.  Menkes syndrome

• Caused by a defective allele on the X chromosome

• Disrupts movement of the metal copper in and out of cells.

• Phenotypes include kinky hair, poor muscle tone, seizures, and low body temperature  Muscular dystrophy

• Wasting away of the muscle

• Caused by the absence of the muscle protein dystrophin  Adrenoleukodystrophy

• X-linked recessive disorder

• Failure of a carrier protein to move either an enzyme or very long chain fatty acid into peroxisomes.

 Hemophilia

• Absence or minimal presence of clotting factor VIII or clotting factor IX • Affected person’s blood either does not clot or clots very slowly.

(64)

X-Linked Recessive Pedigree

64

XB_XB _Xb_Y grandfather

daughter XB_Xb

XB_Y _XB_Y _Xb_Xb

Xb_Y

XB_Xb _grandson

XB_Y _XB_XB _Xb_Y

Key

XB_XB_{= Unaffected female}

XB_Xb _{= Carrier female}

Xb_Xb _{= Color-blind female}

Xb_{Y = Unaffected male}

Xb_{Y = Color-blind male}

X-Linked Recessive Disorders

• More males than females are affected.

• An affected son can have parents who have the normal phenotype.

• For a female to have the characteristic, her father must also have it. Her mother must have it or be a carrier. • The characteristic often skips a generation from the grandfather to the grandson.

(65)

Muscular Dystrophy

65

(Abnormal): Courtesy Dr. Rabi Tawil, Director, Neuromuscular Pathology Laboratory, University of Rochester Medical Center; (Boy): Courtesy Muscular Dystrophy Association; (Normal): Courtesy Dr. Rabi Tawil, Director, Neuromuscular Pathology Laboratory,

University of Rochester Medical Center.

abnormal muscle

normal tissue fibrous