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Section 6.5

Section 6.5. Traits and Probability. Objectives. SWBAT describe what a monohybrid and dihybrid crosses are. SWBAT explain how heredity can be illustrated mathematically. Vocabulary. Punnett square Monohybrid cross Dihybrid cross Testcross Law of independent assortment Probability .

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Section 6.5

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  1. Section 6.5 Traits and Probability

  2. Objectives • SWBAT describe what a monohybrid and dihybrid crosses are. • SWBAT explain how heredity can be illustrated mathematically

  3. Vocabulary • Punnett square • Monohybrid cross • Dihybrid cross • Testcross • Law of independent assortment • Probability

  4. Punnett Squares • Punnett squares illustrate genetic crosses. • The Punnett square is a grid system for predicting all possible genotypes resulting from a cross. • The axes representthe possible gametesof each parent. • The boxes show thepossible genotypesof the offspring. • The Punnett square yields the ratio of possible genotypes and phenotypes.

  5. Punnett Squares A monohybrid cross involves one trait. • Monohybrid crosses examine the inheritance of only one specific trait. • homozygous dominant-homozygous recessive: all heterozygous, all dominant

  6. Punnett Squares Heterozygous X heterozygous cross results in 1:2:1 genotypic ratio. Phenotypic ratio is 3:1 dominant to recessive

  7. Punnett Squares • Heterozygous X homozygous recessive results in a genotypic ratio of 1:1 • Heterozygous X homozygous recessive results in a phenotypic ratio of 1:1 dominant to recessive

  8. Dihybrid Cross: 2 Traits • Mendel’s dihybrid crosses with heterozygous plants yielded a 9:3:3:1 phenotypic ratio. • Mendel’s dihybrid crosses led to his second law,the law of independent assortment. • The law of independent assortment states that allele pairs separate independently of each other during meiosis.

  9. Probability = number of ways a specific event can occur number of total possible outcomes Heredity patterns calculated with probability. • Probability is the likelihood that something will happen. • Probability predicts an average number of occurrences, not an exact number of occurrences. • Probability applies to random events such as meiosis and fertilization.

  10. Probability

  11. Phenotype can depend on interactions of alleles. • In incomplete dominance, neither allele is completely dominant nor completely recessive. • Heterozygous phenotype is intermediate between the two homozygous phenotypes • Homozygous parental phenotypes not seen in F1 offspring

  12. Many genes have more than two alleles.

  13. Polygenic Traits Polygenic traits are the result of two or more genes interacting. They are expressed as gradations. Human height is a polygenic trait.

  14. Polygenic Traits Skin color is a polygenic trait.

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