1. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents TT tt Ee Ee T t
eggs E e Tt E
eggs T t EE
spem
Punnett square Ee T TT Tt
sperm e t Tt tt Ee ee
Offspring
Offspring

2. Blending Inheritance Theories of inheritance in Mendel’s time:
Based on blending
Parents of contrasting appearance produce offspring of intermediate appearance

3. © Ned M. Seidler/Nationa1 Geographic Image Collection
Gregor Mendel
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mendel’s findings were in contrast with this
Particulate theory of inheritance
Involves reshuffling of genes from generation to generation
© Ned M. Seidler/Nationa1 Geographic Image Collection

4. Law of Segregation
Each individual has a pair of alleles for each trait
The alleles segregate (separate) during gamete formation
Each gamete contains only one allele from each pair
Fertilization gives the offspring two factors for each trait

5. Mendel’s Monohybrid Crosses: An Example
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P generation TT tt
P gametes T t
F1 generation Tt
F1 gametes T t T TT Tt
F2 generation
sperm t Tt tt
Offspring
Allele Key
Phenotypic Ratio
T = tall plant
t = short plant 3
tall 1
short

6. Modern Genetics View
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

7. Homologous Chromosomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
sister chromatids
alleles at a
gene locus G g G G g g
Replication R r R R r r S s S S s s
a. Homologous
chromosomes
have alleles for
same genes at
specific loci.
b. Sister chromatids
of duplicated
chromosomes
have same alleles
for each gene. t T t t T T

8. Genotype versus Phenotype
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

9. Genotype versus Phenotype

10. 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 the squares

11. Punnett Square
Can 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 =½x½=¼
The chance of Ee =½x½=¼
The chance of eE =½x½=¼
The chance of ee =½x½=¼

12. Punnett Square Showing Earlobe Inheritance Patterns
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents Ee Ee
eggs E e E EE Ee
spem
Punnett square e Ee e e
Offspring
Allele key
Phenotypic Ratio
E = unattached earlobes
e = attached earlobes 3
unattached earlobes 1
attached earlobes

13. Monohybrid Test cross
Test cross determines genotype of individual having dominant phenotype
Based on the knowledge that individuals with recessive phenotype always known homozygous recessive genotype

14. Monohybrid Test cross
However, individuals with dominant phenotype have unknown genotype
May be homozygous dominant, or Heterozygous

15. Two-Trait Inheritance
Dihybrid cross uses true-breeding plants differing in two traits
Observed phenotypes among F2

16. 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

17. Animation
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18. Sample Dihybrid Problem
Tall is dominant to short and purple is dominant to white in pea plants. Cross two plants that are heterozygous for both traits.

19. Chi-Square Chi-Square Tutorial
In the garden pea, yellow cotyledon color is dominant to green, and inflated pod shape is dominant to the constricted form. Considering both of these traits jointly in self-fertilized dihybrids, the progeny appeared in the following numbers:
193 green, inflated; 184 yellow constricted
556 yellow, inflated; 61 green, constricted
Do these genes assort independently? Support your answer using Chi-square analysis.

20. Gene Linkage
1. How are the scientists results different from Mendel’s work?
2. How did they explore their results?
3. How did the scientists explain their findings?
Genetic linkage is very strong for genes which are located close to each other on the same chromosome. What happens in the case of two genes which are far apart on the same chromosome?

21. Are all alleles completely dominant or recessive?
Incomplete Dominance
The heterozygous is in between the homozygous individuals.
Phenotype reveals genotype without test cross

22. Example
Cross two pink flowers. What genotypes and phenotypes are possible?

23. Co-Dominant
Both alleles are expressed in the phenotype.

24. Example
In humans blood type AB (IAIB) is codominant. What blood types are possible if two people with AB blood type have children?

25. Do any genes have more than two alleles?
Multiple Alleles
The gene has several allelic forms
But each individual still receives two

26. Practice
Mom is Type A and Dad is Type B, what are all the possible blood types for their children?

27. Is each phenotypic trait influenced by only one gene?
Polygenic
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
Result in continuous variation of phenotypes

29. For genes that are on the X chromosome in humans and other mammals, what are the differences in inheritance for males vs. females?

30. X – Linked Inheritance In mammals
The X and Y chromosomes determine gender
Females = XX
Males = XY

31. X-linked = genes that have nothing to do with gender
Carried on the X chromosome and the Y does not have these genes.
Discovered in the early 1900s by a group at Columbia University, headed by Thomas Hunt Morgan.

32. Human X-Linked Disorders
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.
Muscular dystrophy
Wasting away of the muscle
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 a clotting factor VIII, or clotting factor IX
Affected person’s blood either does not clot or clots very slowly.

33. Practice
Cross a male hemophiliac with a female whose father was a hemophiliac. What are the possible genotypes and phenotypes of their children?

34. Human Genetic Disorders/Pedigrees
Autosomal – any gene not on the sex chromosomes
Dominant genetic disorder (brittle bone)
AA and Aa have the disorder
Recessive genetic disorder (cystic fibrosis)
aa has the disorder

35. Autosomal Recessive Pedigree Chart
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. I aa A? II A? Aa Aa A? *
III Aa Aa A? A? IV
Key aa aa A?
aa = affected
Aa = carrier (unaffected)
AA = unaffected
A? = unaffected
(one allele unknown)
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.

36. Autosomal Dominant Pedigree Chart
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. I Aa Aa * II aa Aa A? aa aa aa
III Aa Aa aa aa aa aa
Key
AA = affected
Aa = affected
Autosomal dominant disorders
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.
A? = affected
(one allele unknown)
aa = unaffected •

37. Autosomal Recessive Disorders
Tay-Sachs Disease
Progressive deterioration of psychomotor functions
Cystic Fibrosis
Mucus in bronchial tubes and pancreatic ducts is particularly thick and viscous
Phenylketonuria (PKU)
Lack enzyme for normal metabolism of phenylalanine

38. Courtesy Division of Medical Toxicology, University of Virginia
Methemoglobinemia
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Courtesy Division of Medical Toxicology, University of Virginia

39. Autosomal Dominant Disorders
Neurofibromatosis
Tan or dark spots develop on skin and darken
Small, benign tumors may arise from fibrous nerve coverings
Huntington Disease
Neurological disorder
Progressive degeneration of brain cells
Severe muscle spasms
Personality disorders

40. Pleioptropic Effects
Pleiotropy occurs when a single mutant gene affects two or more distinct and seemingly unrelated traits.
Marfan syndrome have disproportionately long arms, legs, hands, and feet; a weakened aorta; poor eyesight

41. (Left): © AP/Wide World Photos; (Right): © Ed Reschke
Marfan Syndrome
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Connective
tissue defects
Skeleton
Heart and blood vessels
Eyes
Lungs
Skin
Chest wall deformities
Long, thin fingers, arms, legs
Scoliosis (curvature of the spine)
Flat feet
Long, narrow face
Loose joints
Mitral valve
prolapse
Enlargement
of aorta
Lens dislocation
Severe nearsightedness
Stretch marks in skin
Recurrent hernias
Dural ectasia: stretching
of the membrane that
holds spinal fluid
Collapsed lungs
Aneurysm
Aortic wall tear
(Left): © AP/Wide World Photos; (Right): © Ed Reschke

42. X-Linked Recessive Pedigree
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
XBXB
XbY
grandfather
XBY
XBXb
daughter
XBY
XbXb
XbY
XBY
XBXB
XBXb
XbY
grandson
Key
XBXB = Unaffected female
XBXb = Carrier female
XbXb = Color-blind female
XbY = Unaffected male
XbY = 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.
• If a woman has the characteristic, all of her sons will
have it.

43. Muscle Dystrophy fibrous tissue abnormal muscle normal tissue
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
fibrous
tissue
abnormal
muscle
normal
tissue
(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.

44. Terminology Pleiotropy Codominance Epistasis
A gene that affects more than one characteristic of an individual
Sickle-cell (incomplete dominance)
Codominance
More than one allele is fully expressed
ABO blood type (multiple allelic traits)
Epistasis
A gene at one locus interferes with the expression of a gene at a different locus
Human skin color (polygenic inheritance)

45. Review Blending Inheritance Monohybrid Cross Modern Genetics
Law of Segregation
Modern Genetics
Genotype vs. Phenotype
Punnett Square
Dihybrid Cross
Law of Independent Assortment
Human Genetic Disorders

46. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents TT tt Ee Ee T t
eggs E e Tt E
eggs T t EE
spem
Punnett square Ee T TT Tt
sperm e t Tt tt Ee ee
Offspring
Offspring