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Biology

Mr. Karns. Biology. Mendels Laws. 11–3 Exploring Mendelian Genetics. 11-3 Exploring Mendelian Genetics. Independent Assortment. What is the principle of independent assortment?. Independent Assortment. Independent Assortment

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Biology

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  1. Mr. Karns Biology Mendels Laws

  2. 11–3 Exploring Mendelian Genetics 11-3 Exploring Mendelian Genetics

  3. Independent Assortment • What is the principle of independent assortment?

  4. Independent Assortment • Independent Assortment • To determine if the segregation of one pair of alleles affects the segregation of another pair of alleles, Mendel performed a two-factor cross.

  5. Independent Assortment • The Two-Factor Cross: F1 • Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy). • All of the F1 offspring produced round yellow peas (RrYy).

  6. Independent Assortment • The alleles for round (R) and yellow (Y) are dominant over the alleles for wrinkled (r) and green (y).

  7. Independent Assortment • The Two-Factor Cross: F2 • Mendel crossed the heterozygous F1 plants (RrYy) with each other to determine if the alleles would segregate from each other in the F2 generation. • RrYy ×RrYy

  8. Independent Assortment • The Punnett square predicts a 9 : 3 : 3 :1 ratio in the F2 generation.

  9. Independent Assortment • In Mendel’s experiment, the F2 generation produced the following: • some seeds that were round and yellow • some seeds that were wrinkled and green • some seeds that were round and green • some seeds that were wrinkled and yellow

  10. Independent Assortment • The alleles for seed shape segregated independently of those for seed color. This principle is known as independent assortment. • Genes that segregate independently do not influence each other's inheritance.

  11. Independent Assortment • Mendel's experimental results were very close to the 9 : 3 : 3 : 1 ratio predicted by the Punnett square. • Mendel had discovered the principle of independent assortment.

  12. Independent Assortment • 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.

  13. A Summary of Mendel's Principles • A Summary of Mendel's Principles • Genes are passed from parents to their offspring. • If two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive.

  14. A Summary of Mendel's Principles • In most sexually reproducing organisms, each adult has two copies of each gene. These genes are segregated from each other when gametes are formed. • The alleles for different genes usually segregate independently of one another.

  15. Beyond Dominant and Recessive Alleles • What inheritance patterns exist aside from simple dominance?

  16. Beyond Dominant and Recessive Alleles • Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

  17. Beyond Dominant and Recessive Alleles • Incomplete Dominance  • When one allele is not completely dominant over another it is called incomplete dominance. • In incomplete dominance, the heterozygous phenotype is between the two homozygous phenotypes.

  18. Beyond Dominant and Recessive Alleles RR • A cross between red (RR) and white (WW) four o’clock plants produces pink-colored flowers (RW). WW

  19. Beyond Dominant and Recessive Alleles • Codominance  • In codominance, both alleles contribute to the phenotype. • In certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers. • Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color, but appear separately.

  20. Beyond Dominant and Recessive Alleles • Multiple Alleles  • Genes that are controlled by more than two alleles are said to have multiple alleles. • An individual can’t have more than two alleles. However, more than two possible alleles can exist in a population. • A rabbit's coat color is determined by a single gene that has at least four different alleles.

  21. Beyond Dominant and Recessive Alleles • Different combinations of alleles result in the colors shown here. KEY C = full color; dominant to all other alleles cch= chinchilla; partial defect in pigmentation; dominant to ch and c alleles ch = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles Full color: CC, Ccch, Cch, or Cc Chinchilla: cchch, cchcch, or cchc Himalayan: chc, or chch AIbino: cc

  22. Beyond Dominant and Recessive Alleles • Polygenic Traits • Traits controlled by two or more genes are said to be polygenic traits. • Skin color in humans is a polygenic trait controlled by more than four different genes.

  23. Applying Mendel's Principles • Applying Mendel's Principles • Thomas Hunt Morgan used fruit flies to advance the study of genetics. • Morgan and others tested Mendel’s principles and learned that they applied to other organisms as well as plants.

  24. Applying Mendel's Principles • Mendel’s principles can be used to study inheritance of human traits and to calculate the probability of certain traits appearing in the next generation.

  25. Genetics and the Environment • Genetics and the Environment • Characteristics of any organism are determined by the interaction between genes and the environment.

  26. 11–3

  27. 11–3 • In a cross involving two pea plant traits, observation of a 9 : 3 : 3 : 1 ratio in the F2 generation is evidence for • the two traits being inherited together. • an outcome that depends on the sex of the parent plants. • the two traits being inherited independently of each other. • multiple genes being responsible for each trait.

  28. 11–3 • Traits controlled by two or more genes are called • multiple-allele traits. • polygenic traits. • codominant traits. • hybrid traits.

  29. 11–3 • In four o'clock flowers, the alleles for red flowers and white flowers show incomplete dominance. Heterozygous four o'clock plants have • pink flowers. • white flowers. • half white flowers and half red flowers. • red flowers.

  30. 11–3 • A white male horse and a tan female horse produce an offspring that has large areas of white coat and large areas of tan coat. This is an example of • incomplete dominance. • multiple alleles. • codominance. • a polygenic trait.

  31. 11–3 • Mendel's principles apply to • pea plants only. • fruit flies only. • all organisms. • only plants and animals.

  32. END OF SECTION

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