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Using Punnett Squares

Using Punnett Squares. Inherited Traits. If you know the parents’ alleles, you can predict the traits the offspring will have Alleles are alternate forms of the same gene Offspring usually inherit two alleles for each trait

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Using Punnett Squares

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  1. Using Punnett Squares

  2. Inherited Traits • If you know the parents’ alleles, you can predict the traits the offspring will have • Alleles are alternate forms of the same gene • Offspring usually inherit two alleles for each trait • These alleles determine both the genotype and the phenotype of the offspring

  3. Inherited Traits • Alleles can be either dominant or recessive • Example: Tallness (T) is a dominant trait in pea plants, while shortness (t) is a recessive trait • Since each parent contributes only one allele for each gene, an offspring can receive one of three possible combinations of alleles • Two dominant alleles (ex: TT) • Two recessive alleles (ex: tt) • One dominant allele and one recessive allele (ex: Tt)

  4. Inherited Traits • A purebred organism is one that has two matching alleles for a trait • Example: TT or tt • Hybrids are organisms that have two different traits • Example: Tt

  5. Using Punnett Squares • A Punnett square is a tool used to predict the possible genes and traits of offspring • Based on the genes of their parents • A Punnett square is a diagram divided into smaller boxes

  6. Using Punnett Squares • In making a Punnett square, the alleles for each parent are separated • The alleles for one parent are written across the top of the table • The alleles for the other parent are written down the left side of the table • Example: • Mom’s alleles: Bb • Dad’s alleles: bb • Blue Skin: Dominant • Green Skin: Recessive

  7. Using Punnett Squares • Next, the Punnett square is filled in by pairing up the two parent alleles • One from the top and one from the left B b b b B b b b b b B b

  8. Using Punnett Squares • Once the Punnett square is filled, you can summarize the genotypes and phenotypes of the offspring (LEQ 1) • Genotypes: • Bb: 50% chance • bb: 50% chance • Phenotypes: • Blue skin: 50% chance • Green skin: 50% chance

  9. Using Punnett Squares • A cross that shows the inheritance of only one trait is called a monohybrid cross • In some cases, a trait may be controlled by more than one pair of genes • Examples: hair color and eye color • The inheritance of traits that are controlled by more than one pair of genes can be difficult to predict using Punnett squares

  10. Polyhybrid Cross for Eye Color

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