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Punnett Squares

Punnett Squares. DOMINANT/RECESSIVE. Dominant allele is represented by a capital letter. Recessive allele is represented by the SAME letter except in lower-case. EX: (Trait: height) Tall = T Short = t; not s for short.

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Punnett Squares

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  1. Punnett Squares

  2. DOMINANT/RECESSIVE Dominant allele is represented by a capital letter. Recessive allele is represented by the SAME letter except in lower-case. EX: (Trait: height) Tall = T Short = t; not s for short

  3. Misconceptions About Dominant Alleles

  4. Genotype & Phenotype The genetic makeup (set of 2 alleles) of an organism is its genotype The physical appearance of an organism is its phenotype

  5. Genotype vs. Phenotype

  6. Talk to a Partner: Determine the genotype and phenotype of each flower

  7. HOMOZYGOUS & HETEROZYGOUS When both alleles in the pair are the same, the organism is homozygous (purebred) EX: TT or tt When both alleles in the pair are different, the organism is heterozygous (hybrid or carrier) Ex: Tt

  8. Which chromosome set is heterozygous?

  9. Punnett Squares (PSq) • Developed in 1905 by Reginald Punnett. • Used to predict & compare possible genetic variations resulting from a cross • Probabilities, not exact results

  10. PROBABILITY ____________________is the likelihood that a particular event will occur It can be written as a: Fraction ____ Percent ____ Ratio ____ (dominant : recessive) 1/4 25% 1:3

  11. Symbols used in PSq • Original parents  P1 generation • Offspring of the parent plants  F1 generation • Offspring of the F1 generation  F2 generation

  12. Explaining Mendel’s Results using Punnett Squares • Creating Pure breeding P generation PP X PP pp X pp

  13. Explaining Mendel’s Results using Punnett Squares • Creating F1 generation: PP X pp

  14. Explaining Mendel’s Results using Punnett Squares • Creating F2 generation: Pp X Pp

  15. Practice Problem: Monohybrid Crosses: Working w/ PS #1

  16. Now try problems on: • Punnett Squares Practice: Monohybrid Crosses STOP !!

  17. Non-Mendelian Genetics Patterns that don’t follow Mendel’s Rules

  18. 1) Incomplete Dominance • Two different alleles BLEND to form a new phenotype • Ex: Colors in flowers, red + whitepink

  19. 2) Codominance • Two different alleles of the same trait are completely and fully expressed • EX: Red flower & white flower produces a red and white striped flower

  20. Examples

  21. 2. Codominance & Multiple Alleles • Classic Ex: Human blood types - A, B, AB, O • Alleles: IA, IB, i • IA & IB are codominant • i - recessive (ii = type O blood)

  22. Genotype IA IA orIai IB IB orIbi IA IB ii Phenotype

  23. B and O see A as Different! IMMUNE SYSTEM ATTACKS! DONORBLOOD A and AB see Aas “like me” Body images modified from: http://www.new-fitness.com/images/body_shapes.jpg

  24. A and O see B as Different! IMMUNE SYSTEM ATTACKS! DONORBLOOD B and AB see Bas “like me” Body images modified from: http://www.new-fitness.com/images/body_shapes.jpg

  25. DONORBLOOD O ____ can donate to EVERY BLOOD TYPE = _____________________ Nothing on surface to recognize as “NOT SELF” UNIVERSAL DONOR YOU DON’T HAVE ANYTHING I DON’T HAVE! Body images modified from: http://www.new-fitness.com/images/body_shapes.jpg

  26. AB can only GIVE to ABBUT . . . AB ______ can RECEIVE FROM EVERY BLOOD TYPE = ________________________ UNIVERSAL RECIPIENT Body image modified from: http://www.new-fitness.com/images/body_shapes.jpg

  27. Comparison • Codominance • Incomplete dominance

  28. Practice Problem: Incomplete Dominance Working w/ PS #3,4 & 6

  29. Now try problems on: • Punnett Squares Practice: Incomplete/Codominant STOP !!

  30. Non-Mendelian Genetics Patterns that don’t follow the rules Incomplete Dominance Codominance

  31. 3) Sex-linked traits • Traits carried on the sex chromosomes (mostly the x chromosome)

  32. Ex. Colorblindness, hemophilia

  33. 4) Polygenic traits • Trait produced from many alleles on more than one chromosome • Ex. Hair color, skin color, eye color, height

  34. The more genes that contribute to the trait, the more complicated the pattern of expression

  35. Practice Problem: Incomplete Dominance Working w/ PS #2, 5

  36. Now try problems on: • Punnett Squares Practice: Sex-Linked STOP !!

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