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Patterns of Inheritance: Mendelian Genetics Chapter 11 Biology 1010.

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Presentation on theme: "Patterns of Inheritance: Mendelian Genetics Chapter 11 Biology 1010."— Presentation transcript:

1 Patterns of Inheritance: Mendelian Genetics Chapter 11 Biology 1010

2 Gregor Mendel : Father of Genetics A. History 1. Natural selection a. evolution was due to differences in variable traits. b. variation improves chances of survival. 2. Nineteenth century thought favored blending

3 B. Mendel and the experimental approach 1. experienced in plant breeding and mathematics 2. excellent observational abilities 3. used garden peas as the experimental system a. self-fertilize - ability to breed true b. easily identifiable traits c. easy to grow 4. the idea of genetics was unknown to Mendel

4 Terminology A. definitions 1. genes: the instructions for producing a trait 2. locus: location of the gene on a chromosome 3. alleles: variations of genes a. variation is at the molecular level

5 4. homologous chromosomes: 2n organisms have 2 copies of each chromosome a. each chromosome has a copy of the gene which may vary (alleles) 5. homozygous: both alleles are the same 6. heterozygous : alleles are different 7. dominant: one allele is expressed over another 8. recessive: expression of the trait is masked

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7 9. genotype: genetic combination of alleles a. homozygous dominant (AA) b. homozygous recessive (aa) c. heterozygous (Aa) 10. phenotype: observed traits 11. generations a. P - parental generation b. F 1 - first generation

8 Mendel’s Theory of Segregation A. Introduction 1. 2n organisms inherit two genes per trait 2. each gamete contains only one copy of the gene 3. pea crosses

9 B. Monohybrid crosses - one trait 1. two parents that breed true for different phenotypes 2. one form disappears in the first generation, but reappears in the second 3. mathematical analysis a. F 2 offspring shows a 3:1 phenotypic ratio b. ratios represent probabilities 4. Punett squares predict outcome

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13 5. Testcross a. may be used to determine the genotype of a parent b. question - is the parent a AA or Aa individual c. constructing the cross

14 Independent Assortment A. Dihybrid crosses - two traits 1. Does the ratio of one trait effect the ratio of a second trait? 2. first generation traits show both dominant traits 3. second generation traits are expressed in a ratio of 9:3:3:1 4. genes on nonhomologous chromosomes assort independently

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16 B. Modern Interpretation 1. meiosis produces genes with only one copy of each gene (haploid) 2. nonhomologous chromosomes assort independently

17 C. Dominance 1. incomplete dominance - a dominant allele can not completely mask a recessive allele 2. codominance - in heterozygotes, both alleles are expressed a. human AB blood 3. multiple allele systems a. human blood groups

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20 D. Pleiotropy 1. one gene may have several effects a. sickle-cell anemia

21 E. Continuous variation in populations 1. phenotypes may vary by predictable degrees 2. distribution of traits may follow a bell- curve 3. most traits are not qualitative 4. polygenetic inheritance controls many traits such as skin color, height, body form, intelligence

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23 F. Environmental Effects 1. environmental factors may effect the phenotype


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