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11-3 Exploring Mendelian Genetics

11-3 Exploring Mendelian Genetics. Independent Assortment. The two- factor Cross: F1 The two- factor Cross: F2. The two- factor Cross: F1. Mendel crossed true- breeeding plants that produces only round yellow peas (Genotype RRYY) with plants that produces wrinkled green peas (Genotype rryy).

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11-3 Exploring Mendelian Genetics

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  1. 11-3 Exploring Mendelian Genetics

  2. Independent Assortment • The two- factor Cross: F1 • The two- factor Cross: F2

  3. The two- factor Cross: F1 Mendel crossed true- breeeding plants that produces only round yellow peas (Genotype RRYY) with plants that produces wrinkled green peas (Genotype rryy) X

  4. The two- factor Cross: F1 Offspring produces round yellow peas.

  5. The two- factor Cross: F1 • It provides hybrids plants needed for the next cross – the F1 plants to produce the F2 generation.

  6. How is the genotype of the offspring different from the homozygous dominant parent?

  7. The two- factor Cross: F2 • How would the alleles segregate when the F1 plants were crossed to each other to produce an F2 generation? • Each plant in the F1 generation was formed by the fusion of a gamete carrying the dominant RY allele with another gamete carrying the recessive ry alleles. • Would they “segregate independently” so that any combination of alleles was possible?

  8. It produced 556 seeds. In a variation of: 315 were round and yellow 32 were wrinkle and green 209 with other combinations of alleles not found in parents.

  9. Independent Assortment • Genes that segregate independently – genes for seed shape and seed color in pea plants – do not influence each other’s inheritance.

  10. The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes. Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms.

  11. A summary of Mendel’s Principles • The inheritance of biological characteristics is determined by individual unit known as genes. Genes are passed from parents to their offspring. • In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and other may be recessive.

  12. A summary of Mendel’s Principles (2) • In most sexually reproducing organisms, each adult has two copies of each gene – one from each parent. These genes are segregate from each other when gametes are formed. • The alleles for different genes usually segregate independently of one another.

  13. Exceptions in Mendel’s work Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

  14. Incomplete Dominance • This complication is shown on four o’clock plants. • The F1 generation produced by a cross between red- flowered (RR) and white- flowered (WW) and have pink (RW) plants.

  15. Incomplete Dominance • One allele is not completely dominant over another • Heterozygous phenotype is somewhere in between the two homozygous phenotypes.

  16. Codominance • Both alleles contribute to the phenotype. • Heterozygous chicken have a color described as “erminette” speckled with black and white feathers.

  17. Multiple Allele • Many genes have more than two alleles. • More than two possible alleles exist in a population. • A rabbit’s coat color is determined by a single gene that has at least four different alleles.

  18. Polygenic Trait • Traits controlled by two or more genes. • Often show a wide range of phenotypes. • The wide range of skin color in humans comes partly because more than four different genes probably control this trait.

  19. Applying Mendel’s Principles In 1900 Thomas Hunt Morgan he was looking for a model of organism that was small, easy to keep in lab and produce large number of offspring. Fruit fly Drosophila melangaster

  20. Fruit fly Drosophila melangaster • It produces plenty of offspring as many as 100. • Morgan tested all of Mendel’s principles

  21. The basic principles of Mendelian genetics can be used to study the inheritance of human traits and to calculate the probability of certain traits appearing in the next generation.

  22. Genetics and the Environment Characteristics are determined by the interaction between genes and the environment. • Genes affect a sunflower plant’s height and the color of the flower • Some characteristics are also influenced by climate, soil conditions and water availability.

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