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Chapter 11

Chapter 11. Gregor Mendel. Father of Genetics Born in 1822 in the Czech Republic Priest in monastery Fertilization by testing pea plants Cross pollination. Cross Pollination. Genes and Dominance. Gene : a specific characteristic that varies from one individual to another.

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Chapter 11

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  1. Chapter 11

  2. Gregor Mendel • Father of Genetics • Born in 1822 in the Czech Republic • Priest in monastery • Fertilization by testing pea plants • Cross pollination

  3. Cross Pollination

  4. Genes and Dominance • Gene: a specific characteristic that varies from one individual to another. • Alleles: different forms of a gene.

  5. Principle of Dominance • Dominant trait: overshadows the recessive trait • Recessive trait: only can be seen when with another recessive trait

  6. Homozygous: organisms that have two identical alleles for a particular trait.(TT) • True breeding • Heterozygous: organisms that have two different alleles for a particular trait. (Tt) • Hybrid

  7. Terms for Genetic Crosses • Phenotype: physical characteristics • Genotype: genetic makeup • P group: parental group • F1: First offspring or generation • F2: second generation

  8. Rules for Punnett Squares • Determine the symbols for the traits • Determine the genotype of the parents. • Make the cross • Answer the questions

  9. Practice Problem #1 • Mendel found that the allele for tall (T) pea plants is dominant to the allele for short (t). What offspring phenotypes would be expected from the following parents: • Male: TT Female: tt • Male: Tt Female: tt • Male: Tt Female: Tt

  10. Practice Problem #2 • The allele for axial flowers (A) in peas is dominant to the allele for flowers borne terminally (a). What phenotypic ratios would you expect among the offspring of a cross between a known heterozygous axial-flowered plant and one whose flowers are terminal?

  11. Practice Problem #3 • Two drosophilas (fruit flies) with normal wings are crossed. Among 123 progeny, 91 have normal wings and 32 have dumpy wings. • A. which trait is dominant? • B. what were the genotypes of the parents?

  12. Practice Problem #4 • Black fur in guinea pigs is a dominant trait and white is the recessive trait. When a homozygous black (BB) guinea pig is crossed with a homozygous white one (bb), what is the phenotype and genotype of the F1 generation?

  13. Law of Segregation • Alleles segregate from each other during the formation of gametes • EX: allele for tall separates from allele for short

  14. Incomplete Dominance • Cases in which one allele is not completely dominant over another • Heterozygous phenotype is somewhere between the two homozygous phenotypes.

  15. Incomplete Problem • A homozygous red flower is crossed with a homozygous white flower. This produces pink flowers in their offspring. What would the offspring look like if a pink flower cross-pollinated with a red flower?

  16. Codominance • Both alleles contribute to the phenotype. • Both show

  17. Codominance Problem • In certain varieties of chickens, the allele for black feathers is codominant with the allele for white feathers. Offspring are speckled with white and black. What would happen if a chicken who is homozygous black feathers is crossed with a chicken who is speckled.

  18. Multiple Alleles • Genes that have more than two alleles • EX: coat color in rabbits. Determined by a single gene that has at least four different alleles.

  19. Polygenic Traits • Traits controlled by two or more genes • EX: wide range in skin color in humans comes about because more than four different genes control this trait.

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