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Chapter 4

Chapter 4. Heredity and Evolution. Chapter Outline. Genetic Principles Discovered by Mendel Mendelian Inheritance in Humans Non-Mendelian Patterns of Inheritance Mitochondrial Inheritance. Chapter Outline. Modern Evolutionary Theory Definition of Evolution

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Chapter 4

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  1. Chapter 4 Heredity and Evolution

  2. Chapter Outline • Genetic Principles Discovered by Mendel • Mendelian Inheritance in Humans • Non-Mendelian Patterns of Inheritance • Mitochondrial Inheritance

  3. Chapter Outline • Modern Evolutionary Theory • Definition of Evolution • Factors That Produce and Redistribute Variation • Natural Selection Acts on Variation • Review of Genetics and Evolutionary Factors

  4. Genetic PrinciplesDiscovered by Mendel • Gregor Mendel (1822-1884) laid down the basic principles of heredity. • Crossed different strains of purebred plants and studied their progeny. • Worked with common garden peas and considered only one trait at a time. • His work illustrates the basic rules of inheritance.

  5. Principle of Segregation • Genes occur in pairs because chromosomes occur in pairs. • During gamete production, members of each gene pair separate so each gamete contains one member of a pair. • During fertilization, the full number of chromosomes is restored and members of a gene or allele pairs are reunited.

  6. Results of Crosses When One Trait at a Time is Considered

  7. Principle of Independent Assortment • The distribution of one pair of alleles into gametes does not influence the distribution of another pair. • The genes controlling different traits are inherited independently of one another.

  8. Punnett Square

  9. Results of Crosses When 2 Traits Are Considered Simultaneously

  10. Dominant Mendelian Traits in Humans

  11. Dominant Mendelian Traits in Humans

  12. Recessive Mendelian Traits in Humans

  13. Recessive Mendelian Traits in Humans

  14. Mendelian Inheritance in Humans • Over 4,500 human trains are known to be inherited according to Mendelian principles. • The human ABO blood system is an example of a simple Mendelian inheritance. • The A and B alleles are dominant to the O allele. • Neither the A or B allele are dominant to one another; They are codominant and both traits are expressed.

  15. ABO Genotypes and Associated Phenotypes

  16. Pattern of Inheritance of Autosomal Dominant Traits

  17. Inheritance of anAutosomal Dominant Trait

  18. Partial Pedigree for Albinism

  19. Discontinuous Distribution of a Mendelian Trait (ABO Blood Type)

  20. Inherited Genetic Disorders • Genetic disorders can be inherited as dominant or recessive traits. • Dominant disorders are inherited when one copy of a dominant allele is present. • Recessive disorders require the presence of two copies of the recessive allele. • Recessive conditions that affect humans: cystic fibrosis, Tay-Sachs disease, sickle cell anemia, and albinism.

  21. Polygenic Inheritance • Polygenic traits are continuous traits governed by alleles at more than one genetic locus. • Continuous traits show gradations, there is a series of measurable intermediate forms between two extremes. • Skin color is a common example of a polygenic trait it is governed by 6 loci and at least 12 alleles.

  22. Mendelian Traits Comparedwith Polygenic Traits

  23. Frequency of the Sickle-cell Allele Distribution in the Old World

  24. Malaria Distribution in the Old World

  25. Genetic and Environmental Factors • The genotype sets limits and potentials for development and interacts with the environment. • Aspects of the phenotype are influenced by this genetic-environmental interaction. • The environment influences many polygenic traits, such as height. • Mendelian traits are less likely to be influenced by the environment.

  26. Levels of Evolution • These levels are integrated in a way that eventually produces evolutionary change: • Molecular • Cellular • Individual • Population

  27. Mutation and Evolution • Mutation is a molecular alteration in genetic material: • For a mutation to have evolutionary significance it must occur in a gamete (sex cell). • Such mutations will be carried on one of the individual's chromosomes. • During meiosis the chromosome carrying the mutation will assort giving a 50% chance of passing the allele to an offspring.

  28. The Modern Synthesis Evolution is defined as a two-stage process: • The production and redistribution of variation (inherited differences between individuals). • Natural selection acting on this variation (whereby inherited differences, or variation, among individuals differentially affect their ability to reproduce successfully).

  29. Factors That Lead to Increases in Allele Frequencies • Genetic drift occurs in small populations where random factors cause significant changes. • Gene flow occurs when individuals migrate and mate outside their original population. • Differential reproduction occurs when individuals with particular alleles have more offspring than others, leading to changes in allele frequency and evolution.

  30. New Technologies • Polymerase chain reaction (PCR) makes it possible to analyze and identify DNA as small as one molecule and produce multiple copies of the original DNA. • RecombinantDNA techniques allow scientists to transfer genes from the cells of one species into the cells of another. • Geneticmanipulation is controversial due to safety and environmental concerns.

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