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Predicting Inheritance using Punnett Squares

Predicting Inheritance using Punnett Squares. Unit 5: Genetics Chapter 11-2. Let’s Review our Vocab !. Dominant traits cover up Recessive traits Dominant Allele = capital letter (B) Recessive Allele = lower case letter ( b ). P = Parents. F1 = first generation offspring.

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Predicting Inheritance using Punnett Squares

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  1. Predicting Inheritance using Punnett Squares Unit 5: Genetics Chapter 11-2

  2. Let’s Review our Vocab! • Dominant traits cover up Recessive traits • Dominant Allele = capital letter (B) • Recessive Allele = lower case letter (b) P = Parents F1 = first generation offspring F2 = second generation offspring

  3. Dominant or Recessive? • B=Black b=white • Bb: Dom or Rec? Color? • T=Tall t= short • TT: Dom or Rec? Height? • P=Purple p=white • pp?: Dom or Rec? Color?

  4. Genotype: the actual alleles for a trait • Represented by letters: AA, aa, Aa • Homozygous Dominant: 2 dominant alleles (AA) (purebred) • Homozygous Recessive: 2 recessive alleles (aa) (purebred) • Heterozygous: 1 dominant allele & 1 recessive allele (Aa) (hybrid)

  5. Homozygous or Heterozygous? • BB • Kk • ff • Homozygous dominant • Heterozygous • Homozygous recessive Purebred or Hybrid? • rr • Ww • NN • purebred • hybrid • purbred

  6. Phenotype: how the trait is seen • Ex: Guinae pig fur color: black or white P = Parents F1 = first generation offspring F2 = second generation offspring

  7. Genotype or Phenotype? • Black • Bb • tt • Short • KK • Pp • Tall • White • Phenotype • Genotype • Genotype • Phenotype • Genotype • Genotype • Phenotype • Phenotype

  8. PunnettSquares • Used to predict the traits of each possible offspring during a cross • Five Step Plan • 1) Legend • 2) Parents • 3)Punnett square-set it up • 4) Punettsquare-fill it in • 5) Answers in boxes

  9. 5-Step Plan for Punnett Squares Flee Map 5-Step Plan 1) Legend 2) Parents 3) Punnett Square: Set it up 4) Punnett Square: Fill it in 5) Answers Pg 10

  10. Sample ProblemYou do NOT have to write this slide! • In guinea pigs, Black (B) is dominant to White (b) • Black guinea pig (BB) x White guinea pig (bb) • What are the chances that the offspring will be black? White? • How many offspring will be black? How many will be white?

  11. Five-Step Plan • 1) Legend • Always use the first letter of the dominant trait to represent your alleles. (ex: in this case, we use B for black) • Set up a table: Black Black White

  12. 2) Parents - Write this as a “cross” • BB x bb

  13. 3) Punnett Square - Set it up • Draw a square and divide into four sections • Write the genotype (letters) from one parent on top (one letter per box) • Write the genotype from the other parent along the left side B B b b

  14. 4) PunnettSquare - Fill it in • Fill in the boxes with one letter from the top and one letter from the left (2 letters per box) B B b b B b B b B b B b

  15. 5) Answers • Each box = a 25% chance of offspring inheriting that genotype • Always put a box around your final answer!!! B B 100% Black offspring 0% White offspring Ratio: 4 : 0 OR 1 : 0 (Black : White) b b B b B b B b B b

  16. Now you practice on the whiteboard! • Now we have COMPLETELY answered the question and we are done! • Always double check!

  17. Whiteboards • Keep your notes & flow map in front of you. • Please do not draw on whiteboard unless instructed. • For each problem you will do steps 1 & 2 (legend & parents) first. • You will then do steps 3-5 (Punnett square and answers).

  18. Example:Purple Flower (PP) x White Flower (pp) P P p p Pp Pp Pp Pp What % of the offspring will be Purple? White? What is the ratio of purple : white? (Hint: how many of each & reduce) 100 % Purple 0% White 1: 0

  19. Example:Tall (Tt) x short (tt) tt T t Tt Tt tt tt What % of the offspring will be Tall? Short? What is the ratio of tall : short? (Hint: how many of each & reduce) 50 % Tall 50% Short 1: 1

  20. Example:Brown eyes (Bb) x Brown eyes (Bb) B b B b BB Bb Bb bb What % of the offspring will be Brown eyes? Blue eyes? What is the ratio of brown eyes : blue eyes? (Hint: how many of each) 75 % Brown 25% Blue 3: 1

  21. Example:Dimples (DD) x No Dimples (dd) D D d d Dd Dd Dd Dd What % of the offspring will have dimples? No dimples? What is the ratio of dimples : no dimples? (Hint: how many of each & reduce) 100 % Dimples 0% No dimples 1: 0

  22. Normal thumbs (T) are dominant to hitchiker’s thumbs (t). A man with hitchiker’s thumb marries a women that is heterozygous for a normal thumb. tt T t Tt Tt tt tt % of Normal thumbs? % Hitchiker’s thumbs? Ratio? 50 % Normal 50% Hitchiker’s 1: 1

  23. Free earlobes (F) are dominant to attached earlobes (f). A man with attached earlobes marries a women that is homozygous for free earlobes. ff F F Ff Ff Ff Ff % Free Earlobes? % Attached earlobes? Ratio? 100 % Free 0% Attached 1: 0

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