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Punnett Squares and Determining Offspring Traits

Learn about Punnett squares and how they are used to determine the traits of offspring in genetics. Explore different scenarios and answer questions about genotype, phenotype, and the probability of inheriting specific traits.

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Punnett Squares and Determining Offspring Traits

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  1. TOPIC: GeneticsAIM: What are Punnett Squares?

  2. TOPIC:Genetics AIM: How do we use Punnett Squares to determine the traits of offspring? DO NOW: • P = purple flower, p = white flowers • Identify the 3 possible gene combinations and for each, give the phenotype and genotype.

  3. Do you have your mothers eyes? Do you have your father’s eyes? Both! While your eye color may match they eyes of only one of your parents, you actually inherited a PAIR of eye color genes from EACH PARENT. Your mother and father each gave you two eye color genes called BEY and GEY in different forms (alleles). Your BEY gene may have 2 brown alleles (BB) or two blue alleles (bb) or one of each (Bb). Your GEY gene can have 2 green alleles (GG), two blue alleles (gg) or one of each (Gg). Your eye color depends on the combination you have.

  4. Brown (B) is dominant over all other alleles, green (G) is dominant over blue (b and g) and blue alleles are never dominant. BBGG = brown BBgg = brown BbGg = brown BBGg = brown BbGG = brown Bbgg = brown bbGG = green bbGg = green bbgg = blue This 2 gene model works for most eye colors but not for people with grey, hazel or dark eyes.

  5. probability Possibility that an event may/may not happen

  6. ¼ = 25% • 2/4 = 50% • 3/4 = 75% • 4/4 = 100%

  7. Punnett Square Special chart Shows possible gene combos of offspring on inside. Parent Gamete possibilities go on the outside.

  8. T T Example: 1. T = tall t = short TT x tt t t T t T T t t T t

  9. T T T t t T t t T t T t • Phenotype = • 100% (4/4) tall • Genotype = • 100% hybrid

  10. B b 2. B = Black fur b = white fur Bb x Bb B B B B b b B b b b

  11. B b B b B B B b B b b b • Phenotype= 75% black, 25 % white • Genotype= 50% hybrid • 25% pure dominant • 25% pure recessive

  12. 3. Red is dominant in flowers & white is recessive. Cross a heterozygous flower with a homozygous dominant flower. • R = redr = white • Rr x RR

  13. Rr x RR R r • Phenotype= R r R R R • 100% red R R R R r • Genotype = • 50% pure dominant • 50% hybrid

  14. 4. One dog carries heterozygous, black fur traits, and the other carries homozygous recessive white traits. What are the chances of having a puppy with black fur? • B = black, b = white • Bb x bb

  15. B b • Bb x bb b b b B b Answer: 50% chance of having a puppy with black fur b B b b b

  16. Review: 1. What is the difference between a genotype and a phenotype?  2. What did Mendel use in his first experiment to test his hypothesis about genes?  ­ 3. A person is very short.  They are homozygous recessive for this trait.  Give the genotype (letters) for this person.  4. Correctly cross a  blue eyed person with a  heterozygous brown eyed  person.  Give the phenotype and genotype.    

  17. 5. Red hair (R) is dominant over blonde hair (r). Make a cross between a heterozygous red head and a blonde. R r r r

  18. 6. Cross a heterozygous brown haired rabbit with a homozygous recessive white haired rabbit. Determine phenotype & genotype. Phenotype: Bb x bb 50% brown haired 50% white haired b b Bb Bb B b Genotype: 50% hybrid 50% pure recessive bb bb

  19. 7. Black eyes (R) is dominant over red eyes (r) in rats. Make a cross between a homozygous rat with black eyes and a rat with red eyes. R R What is the possibility of a red eyed offspring? r r 0%

  20. 8. Cross a homozygous dominant long haired guinea pig with a heterozygous long haired guinea pig. Phenotype: LL x Ll 100% long hair L l Genotype: LL Ll L L 50% hybrid 50% pure dominant LL Ll

  21. 9. Cross a heterozygous wrinkly elephant with another heterozygous wrinkly elephant. Phenotype: Ww x Ww 75% wrinkly 25% no wrinkles W w WW Ww W w Genotype: 50% hybrid 25% pure dominant 25% pure recessive Ww ww

  22. 10. The freckles trait is considered to be dominant. A couple a wonders if their children will have freckles. The man has freckles but his mother did not. The woman in this couple has no freckles. Create a Punnett Square and determine the phenotype and genotype of their possible offspring. Phenotype: Ff x ff 50% freckles 50% no freckles F f Ff ff f f Genotype: Ff ff 50% hybrid 50% pure recessive

  23. 11. The gene for free ear lobes is dominant. The gene for attached ear lobes is recessive. Complete the Punnett square to show the cross between two heterozygous parents and determine genotype & phenotype. Phenotype: F f 75% free 25% attached FF Ff F Genotype: ff 50% hybrid 25% pure recessive 25% pure dominant f Ff

  24. 12. I = cleft chin i = smooth chin Cross these 2 parents: Ii x ii Determine phenotype & genotype. Phenotype: I i 50% cleft chin 50% smooth chin Ii ii i Genotype: 50% hybrid 50% pure recessive Ii ii i

  25. 13. WHICH OF THE FOLLOWING HAS THE hh GENOTYPE? • A. 1 & 3 C. 4 • B. 2 D. NONE H h H 1 4 3 h 2 • 14. WHICH OF THE FOLLOWING IS A TRUE STATEMENT? • INDIVIDUAL 4 IS RECESSIVE • INDIVIDUALS 1 & 3 ARE HETEROZYGOUS • INDIVIDUAL 2 IS DOMINANT • ALL INDIVIDUALS ARE FEMALE

  26. 15. IF B IS THE ALLELE FOR BLACK FUR AND b IS THE ALLELE FOR WHITE FUR, WHAT PERCENT WOULD BE BLACK? A. 25% C. 100% B. 50% D. 75% B b B Bb BB Bb b bb 16. WHAT FRACTION IS HOMOZYGOUS DOMINANT IN THE ABOVE CROSS? A.1/2B. ¼ C. 1/3 D. 4/4

  27. 17. In dogs, hereditary deafness is caused by a recessive gene, “d.” A kennel owner has a male dog that she wants to use for breeding if possible. The dog can hear, so the owner knows his genotype is either DD or Dd. If the dog’s genotype is Dd, the owner does not wish to use him for breeding so that the deafness gene will not be passed on. This can be tested by breeding the dog to a deaf female (dd). • A. Draw the Punnett squares to illustrate these two possible crosses. DD x dd Dd x dd D D D d Dd Dd Dd dd d d d d Dd Dd Dd dd

  28. DD x dd Dd x dd B. In each case, what percentage of the offspring would be expected to be hearing? deaf? C. What is the genotype of the male dog the owner can use? D D D d Dd Dd Dd dd d d d d Dd Dd Dd dd B. Hearing = 100% Deaf = 0% B. Hearing = 50% Deaf = 50% C. pure dominant (DD)

  29. Review: 1. What is the difference between a genotype and a phenotype?  2. What did Mendel use in his first experiment to test his hypothesis about genes?  ­ 3. A person is very short.  They are homozygous recessive for this trait.  Give the genotype (letters) for this person.  4. Correctly cross a  blue eyed person with a  heterozygous brown eyed  person.  Give the phenotype and genotype.    

  30. PUNNETT SQUARES WORKSHEET • T = tall, t = short Cross a heterozygous tall plant with a short plant. • Phenotype= Tt x tt • 50% tall, 50% short T t • Genotype = t t • 50% pure recessive • 50% hybrid

  31. PUNNETT SQUARES WORKSHEET 2. G = green, g = yellow Cross a pure green plant with a hybrid plant. GG x Gg • Phenotype= G G • 100% green G g • Genotype = • 50% pure dominant • 50% hybrid

  32. PUNNETT SQUARES WORKSHEET 3. A man with blue eyes marries a woman who is heterozygous for brown eyes. If brown eyes are dominant, what are the chances of having a blue eyed child? Also, give the phenotypes and genotyes. bb x Bb • 50% chance of blue eyes b b • Phenotype= • 50% brown, 50 % blue B b • Genotype = • 50% pure recessive • 50% hybrid

  33. PUNNETT SQUARES WORKSHEET 4. In tomatoes, red fruit color is dominant to yellow fruit color. Predict the phenotypes and genotypes of the offspring by crossing a homozygous dominant parent with a homozygous recessive parent. RR x rr R R • Phenotype= • 100% red r r • Genotype = • 100% hybrid

  34. Punnett Squares: Human Characteristics 1. B = brown eyes, b = blue eyes Mom = Bb Dad = BB B b • Genotype= • Phenotype= B B • 50% pure dominant • 100% brown eyes • 50% hybrid

  35. Punnett Squares: Human Characteristics 2. Curly hair is recessive, and straight hair is dominant. A woman with curly hair marries a man who is homozygous dominant for straight hair. cc x CC c c • Genotype= • Phenotype= C C • 100% hybrid • 100% straight hair

  36. Punnett Squares: Human Characteristics 3. Black hair is homozygous dominant. Brown hair is heterozygous. Blonde hair is homozygous recessive. A woman with brown hair marries a man with brown hair. Bb x Bb B b • Genotype= • Phenotype= B b • 50% hybrid • 50% brown hair • 25% pure • dominant • 25% black hair • 25% blonde hair • 25% pure • recessive

  37. Punnett Squares: Human Characteristics 4. Attached earlobes are dominant over free hanging earlobes. Mom = BB Dad = bb BB x bb B B • Genotype= • Phenotype= b b • 100% hybrid • 100% attached

  38. 7R Punnett Squares Homework • 1. A green pea plant (Gg) is crossed with a yellow pea plant (gg). G g • Phenotype= • 50% green g g • 50% yellow • Genotype= • 50% hybrid • 50% pure recessive

  39. 7R Punnett Squares Homework • 2. A tall plant (TT) is crossed with a tall plant (Tt). T T • Phenotype= • 100% tall T t • Genotype= • 50% hybrid • 50% pure dominant

  40. 7R Punnett Squares Homework • 3. A tall plant (Tt) is crossed with a short plant (tt). T t • Phenotype= • 50% tall t t • 50% short • Genotype= • 50% hybrid • 50% pure recessive

  41. 7R Punnett Squares Homework • 4. A red flower (Rr) is crossed with a white flower (rr). R r • Phenotype= • 50% red r r • 50% white • Genotype= • 50% hybrid • 50% pure recessive

  42. 7R Punnett Squares Homework • 5. A white flower (rr) is crossed with a white flower (rr). r r • Phenotype= • 100% white r r • Genotype= • 100% pure recessive

  43. 7R Punnett Squares Homework • 6. A black chicken (BB) is crossed with a black chicken (BB). B B • Phenotype= • 100% black B B • Genotype= • 100% pure dominant

  44. 7R More Punnett Squares continued… • 1. A homozygous dominant brown mouse is crossed with a heterozygous brown mouse (tan is the recessive color). • BB x Bb • Phenotype= • 100% brown B B • Genotype= B b • 50% hybrid • 50% pure dominant

  45. 7R More Punnett Squares continued… • 2. Two heterozygous white (brown fur is recessive) rabbits are crossed. • Bb x Bb • Phenotype= • 75% white B b • 25% brown • Genotype= B b • 50% hybrid • 25% pure recessive • 25% pure dominant

  46. 7R More Punnett Squares continued… • 3. Two heterozygous red flowers (white flowers are recessive) are crossed. • Rr x Rr • Phenotype= • 75% red R r • 25% white • Genotype= R r • 50% hybrid • 25% pure recessive • 25% pure dominant

  47. 7R More Punnett Squares continued… • 4. A homozygous tall plant is crossed with a heterozygous tall plant (short is the recessive size). • TT x Tt • Phenotype= • 100% tall T T • Genotype= T t • 50% hybrid • 50% pure dominant

  48. 7R More Punnett Squares continued… • 5. A heterozygous white rabbit is crossed with a homozygous black rabbit. • Ww x ww • Phenotype= • 50% white W w • 50% black • Genotype= w w • 50% hybrid • 50% pure recessive

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