1. Mendelian Patterns of inheritance
Mader Biology Chapter 11

2. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Outline
Blending Inheritance
Monohybrid Cross
Law of Segregation
Modern Genetics
Genotype vs. Phenotype
Punnett Square
Dihybrid Cross
Law of Independent Assortment
Human Genetic Disorders

3. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Gregor Mendel
Austrian monk
Studied science and mathematics at 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 early 1860s
Had no knowledge of cells or chromosomes
Did not have a microscope

4. Biology, 9th ed,Sylvia Mader
Gregor Mendel
Chapter 11
Mendelian Inheritance

5. Fruit and Flower of the Garden Pea
Biology, 9th ed,Sylvia Mader
Fruit and Flower of the Garden Pea
Chapter 11
Mendelian Inheritance

6. Garden Pea Traits Studied by Mendel
Biology, 9th ed,Sylvia Mader
Garden Pea Traits Studied by Mendel
Chapter 11
Mendelian Inheritance

7. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Blending Inheritance
Theories of inheritance in Mendel’s time:
Based on blending
Parents of contrasting appearance produce offspring of intermediate appearance
Mendel’s findings were in contrast with this
He formulated the particulate theory of inheritance
Inheritance involves reshuffling of genes from generation to generation

8. One-Trait Inheritance
Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
One-Trait Inheritance
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
Formulated the Law of Segregation

9. Mendel’s Monohybrid Crosses: An Example
Biology, 9th ed,Sylvia Mader
Mendel’s Monohybrid Crosses: An Example
Chapter 11
Mendelian Inheritance

10. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
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
Fertilization gives the offspring two factors for each trait

11. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
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

12. Homologous Chromosomes
Biology, 9th ed,Sylvia Mader
Homologous Chromosomes
Chapter 11
Mendelian Inheritance

13. Genotype Versus Phenotype
Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Genotype Versus Phenotype
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

14. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
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

15. Punnett Square Showing Earlobe Inheritance Patterns
Biology, 9th ed,Sylvia Mader
Punnett Square Showing Earlobe Inheritance Patterns
Chapter 11
Mendelian Inheritance

16. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Monohybrid Testcross
Individuals with recessive phenotype always have the homozygous recessive genotype
However, Individuals with dominant phenotype have indeterminate genotype
May be homozygous dominant, or
Heterozygous
Test cross determines genotype of individual having dominant phenotype

17. One-Trait Test Cross Unknown is Heterozygous
Biology, 9th ed,Sylvia Mader
One-Trait Test Cross Unknown is Heterozygous
Chapter 11
Mendelian Inheritance

18. One-Trait Test Cross Unknown is Homozygous Dominant
Biology, 9th ed,Sylvia Mader
One-Trait Test Cross Unknown is Homozygous Dominant
Chapter 11
Mendelian Inheritance

19. Two-Trait Inheritance
Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Two-Trait Inheritance
Dihybrid cross uses true-breeding plants differing in two traits
Observed phenotypes among F2 plants
Formulated 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

20. Two-Trait (Dihybrid) Cross
Biology, 9th ed,Sylvia Mader
Two-Trait (Dihybrid) Cross
Chapter 11
Mendelian Inheritance

21. Biology, 9th ed,Sylvia Mader
Two-Trait Test Cross
Chapter 11
Mendelian Inheritance

22. Human Genetic Disorders
Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Human Genetic Disorders
Autosome - Any chromosome other than a sex chromosome
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 disorder
Other genetic disorders are autosomal recessive
An individual with AA does NOT have disorder
An individual with Aa does NOT have disorder, but is a carrier
An individual with aa DOES have the disorder

23. Autosomal Recessive Pedigree Chart
Biology, 9th ed,Sylvia Mader
Autosomal Recessive Pedigree Chart
Chapter 11
Mendelian Inheritance

24. Autosomal Dominant Pedigree Chart
Biology, 9th ed,Sylvia Mader
Autosomal Dominant Pedigree Chart
Chapter 11
Mendelian Inheritance

25. Autosomal Recessive Disorders
Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Autosomal Recessive Disorders
Tay-Sachs Disease
Progressive deterioration of psychomotor functions. Lipid accumulation in brain cells. Death in childhood
Cystic Fibrosis
Mucus in bronchial tubes and pancreatic ducts is particularly thick and viscous
Phenylketonuria (PKU)
Lack enzyme for normal metabolism of phenylalanine. Mental retardation
Albinism- lack of pigment (melanin)
Sickle Cell (homozygous)

26. Cystic Fibrosis Therapy
Biology, 9th ed,Sylvia Mader
Cystic Fibrosis Therapy
Chapter 11
Mendelian Inheritance

27. Autosomal Dominant Disorders
Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Autosomal Dominant Disorders
Alzheimers (mental deterioration)
Achondroplasia (dwarfism)
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

28. A Victim of Huntington Disease
Biology, 9th ed,Sylvia Mader
A Victim of Huntington Disease
Chapter 11
Mendelian Inheritance

29. Huntington Disease: Normal and Diseased Brain
Biology, 9th ed,Sylvia Mader
Huntington Disease: Normal and Diseased Brain
Chapter 11
Mendelian Inheritance

30. Beyond simple mendelian inheritance

31. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Incomplete Dominance
Heterozygote has phenotype intermediate between that of either homozygote
Ex: hybrid flower has pink (intermediate) phenotype
Each allele is expressed incompletely
Phenotype reveals genotype without test cross

32. Codominance
Instead of blending, the heterozygote expresses both phenotypes intermittently
Both alleles are dominant and expressed completely.

33. Multiple Allelic Traits
Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Multiple Allelic Traits
Some traits controlled by multiple alleles
The gene exists in several allelic forms (but each individual only has two)
ABO blood types
The alleles:
IA = A antigen on red cells, anti-B antibody in plasma
IB = B antigen on red cells, anti-A antibody in plasma
i = Neither A nor B antigens, both antibodies
Phenotype (Blood Type)
Genotype
A (actually AA or AO)
IAIA or IAi
B (actually BB or BO)
IBIB or IBi AB
IAIB
O (actually OO) ii

34. Inheritance of Blood Type
Biology, 9th ed,Sylvia Mader
Inheritance of Blood Type
Chapter 11
Mendelian Inheritance

35. Polygenic Inheritance
Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
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
Result in continuous variation of phenotypes

36. Inheritance of Skin Color

37. Biology, 9th ed,Sylvia Mader
Height in Human Beings
Chapter 11
Mendelian Inheritance

38. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Pleiotropy
A gene that affects more than one characteristic of an individual
Examples
Sickle-cell
Albinoism
Cystic Fibrosis

39. Epistasis
A gene at one locus interferes with the expression of a gene at a different locus
Epi – above
Stasis – stand
Ex: color patterns of pigeons

40. Environment and Phenotype: Himalayan Rabbits
Biology, 9th ed,Sylvia Mader
Environment and Phenotype: Himalayan Rabbits
Chapter 11
Mendelian Inheritance

41. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendelian Inheritance
Review
Blending Inheritance
Monohybrid Cross
Law of Segregation
Modern Genetics
Genotype vs. Phenotype
Punnett Square
Dihybrid Cross
Law of Independent Assortment
Human Genetic Disorders