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Chapter 11

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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.