Solomon IM Ch 11

Solomon IM Ch 11 - Chapter11: 11 LectureOutline I A 1 2

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Chapter 11: The Basic Principles of Heredity 103 11 The Basic Principles of Heredity Lecture Outline I. Mendel’s principles of inheritance A. Other plant breeders at the time of Mendel knew two main facts. 1. Hybrid plants from true breeding parents are similar. 2. When hybrid offspring are self fertilized, their offspring show a variety of traits. B. Mendel did his experiments primarily on the garden pea, Pisum sativum. 1. Peas were easy to grow, and many varieties were readily available. 2. Peas may be self or cross fertilized, as they have perfect flowers. a) Pollen from an anther may be dusted onto a stigma. b) Cross fertilization may be prevented by bagging the flower. 3. Mendel obtained and verified pea plants’ true breeding lines. a) True breeding plants, when self pollinated, produce offspring all possessing the same visible trait as the parent plant (e.g., the same phenotype). 4. Mendel chose 7 clearly identifiable pairs of contrasting traits and the accompanying true breeding plants. 5. Mendel first crossed true breeding plants with contrasting traits. a) These parental plants (the P generation) produced the first filial generation (the F 1 generation). b) The F 1 generation plants all possessed the trait of only one of the two parents. c) When the F 1 plants self pollinated, the resulting F 2 generation had characteristics of both of the P generation plants. d) These experiments showed that the hereditary factors had not been lost in the F 1 generation, but were somehow masked. C. Mendel’s experiments disproved the idea of blending inheritance. 1. Mendel proposed that inherited characteristics are controlled by two hereditary “factors” (genes in modern terminology). 2. The term dominant is now used for the traits seen in the F 1 generation, the term recessive for the trait hidden in the F 1 generation. 3. Alternate forms of a gene are now referred to as alleles. D. The principle of segregation states that alleles separate before gametes are formed. 1. The alleles from the male and female gametes do not mix in any way (the principle of segregation). E. Segregation is due to the separation of homologous chromosomes during meiosis. Alleles occupy corresponding loci on homologous chromosomes. 1. The term locus may refer to the location of a gene on a chromosome as well as to the type of gene controlling a characteristic. 2. Alleles are the variations of a gene that govern the same feature. 3. Alleles are denoted by a letter or letters; dominant genes are typically denoted by a capital letter, recessive genes with a lower case letter.
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Instructor’s Manual for Solomon, Berg, and Martin’s Biology, 9 th Edition 104 4. A monohybrid cross involves individuals with different alleles of a given locus.
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