1. Mendelian Patterns of Inheritance
Chapter 11
Mader: Biology 8th Ed.

2. Law of Independent Assortment Human Genetic Disorders
Outline
Blending Inheritance
Monohybrid Cross
Law of Segregation
Modern Genetics
Genotype vs. Phenotype
Punnett Square
Dihybrid Cross
Law of Independent Assortment
Human Genetic Disorders
Mader: Biology 8th Ed.

3. Studied science and mathematics at University of Vienna.
Gregor Mendel
Austrian monk who formulated fundamental laws of heredity in early 1860s.
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.
Mader: Biology 8th Ed.

4. Blending Inheritance
At the time, most breeders believed parents of contrasting appearance always produce offspring of intermediate appearance.
Mendel’s experiments helped him formulate the particulate theory of inheritance.
Inheritance involves reshuffling of genes from generation to generation.
Mader: Biology 8th Ed.

5. Garden Peas
Mader: Biology 8th Ed.

6. One-Trait Inheritance
Mendel performed cross-breeding experiments between true-breeding plants.
Chose varieties that differed in only one trait (monohybrid cross)
Performed reciprocal crosses
Parental generation = P
First generation offspring = F1
Second generation offspring = F2
Formulated law of segregation
Mader: Biology 8th Ed.

7. Mendel’s Monohybrid Cross
Mader: Biology 8th Ed.

8. Mendel’s Monohybrid Cross
Mader: Biology 8th Ed.

9. Each individual has two factors for each trait.
Law of Segregation
Each individual has two factors for each trait.
The factors segregate during gamete formation.
Each gamete contains only one factor from each pair of factors.
Fertilization gives each new individual two factors for each trait.
Mader: Biology 8th Ed.

10. Homozygous = identical alleles Heterozygous = different alleles
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
Mader: Biology 8th Ed.

11. Homologous Chromosomes
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12. Genotype Versus Phenotype
Refers to the alleles an individual receives at fertilization.
Phenotype
Refers to the physical appearance of the individual.
Mader: Biology 8th Ed.

13. Every possible combination of alleles is placed within the squares.
Punnett Square
All possible kinds of sperm are lined up on one axis, and all possible kinds of eggs are lined up on the other axis.
Every possible combination of alleles is placed within the squares.
Mader: Biology 8th Ed.

14. Genetic Inheritance in Humans
Mader: Biology 8th Ed.

15. Testcross
A monohybrid testcross is used to determine if an individual with the dominant phenotype is homozygous dominant or heterozygous for a particular trait.
Mader: Biology 8th Ed.

16. Testcross
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17. Two-Trait Inheritance
Mendel performed cross using true-breeding plants differing in two traits.
Dihybrid Cross
Observed phenotypes among F2 plants.
Formulated law of independent assortment
Mader: Biology 8th Ed.

18. Law of Independent Assortment
Each pair of factors segregates independently of the other pairs.
All possible combinations of factors can occur in the gametes.
Mader: Biology 8th Ed.

19. Dihybrid Cross
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20. Dihybrid Cross
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21. Two-Trait Testcross
A two-trait testcross is used to determine if an individual is homozygous dominant or heterozygous for either of the two traits.
Mader: Biology 8th Ed.

22. Two-Trait Testcross
Mader: Biology 8th Ed.

23. Human Genetic Disorders
Autosome - Any chromosome other than a sex chromosome.
When a genetic disorder is autosomal dominant, an individual with AA or Aa has the disorder.
When a genetic disorder is autosomal recessive, only aa individuals have the disorder.
Carriers - Individuals unaffected by a disorder but can have an affected child.
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24. Autosomal Recessive Pedigree
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25. Autosomal Dominant Pedigree
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26. 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
Lack enzyme for normal metabolism of phenylalanine.
Mader: Biology 8th Ed.

27. 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 leading to progressive degeneration of brain cells, in turn causing severe muscle spasms and personality disorders.
Mader: Biology 8th Ed.

28. Incomplete Dominance
Exhibited when the heterozygote has an intermediate phenotype between that of either homozygote.
Mader: Biology 8th Ed.

29. Incomplete Dominance
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30. Multiple Allelic Traits
When a trait is controlled by multiple alleles, the gene exists in several allelic forms.
ABO blood types
Phenotype Genotype
A IAIA,IAi
B IBIB,IBi
AB IAIB
O ii
Mader: Biology 8th Ed.

31. Inheritance of Blood Type
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32. Polygenic Inheritance
Occurs when a trait is governed by two or more sets of alleles.
Each dominant allele has a quantitative effect on the phenotype, and these effects are additive.
Result in continuous variation of phenotypes.
Mader: Biology 8th Ed.

33. Height in Human Beings
Mader: Biology 8th Ed.

34. Sickle-cell (incomplete dominance)
Terminology
Pleiotropy - 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)
Mader: Biology 8th Ed.

35. Environment and Phenotype
Himalayan Rabbits - Enzyme coding for black fur is active only at low temperatures.
Black fur only occurs on extremities.
Mader: Biology 8th Ed.

36. Law of Independent Assortment Human Genetic Disorders
Review
Blending Inheritance
Monohybrid Cross
Law of Segregation
Modern Genetics
Genotype vs. Phenotype
Punnett Square
Dihybrid Cross
Law of Independent Assortment
Human Genetic Disorders
Mader: Biology 8th Ed.

37. Mader: Biology 8th Ed.