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Bell Work

Bell Work. In pigeons, the allele B produces ash-red feathers. The allele b produces blue feathers. The B allele is dominant to the b allele. A pigeon with genotype Bb is crossed with a pigeon with genotype bb . What percent of the offspring are expected to have ash-red feathers?

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Bell Work

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  1. Bell Work • In pigeons, the allele B produces ash-red feathers. The allele b produces blue feathers. The B allele is dominant to the b allele. • A pigeon with genotype Bb is crossed with a pigeon with genotype bb. What percent of the offspring are expected to have ash-red feathers? • Justify your answer. You do not need to copy the question.

  2. Dihybrid Cross:a cross that shows the possible offspring for two traits Coat Texture: R: Rough r: Smooth Fur Color: B: Black b: White In this example, we will cross a heterozygous individual with another heterozygous individual. Their genotypes will be: BbRr x BbRr

  3. Dihybrid Cross BbRr x BbRr Step 1: Find ALL possible gametes that can be made from each parent. Remember, each gamete must have one B and one R.

  4. Dihybrid Cross BbRr x BbRr Possible gametes: BR Br bR br Step 2: Arrange all possible gametes for one parent on the top of your Punnett Square and the other parent on the side

  5. BR Br bR br BR Br bR br Dihybrid Crosses:a cross that shows the possible offspring for two traits BbRr x BbRr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth Step 3: Fill in the Punnett Square (find the possible genotypes of the offspring)

  6. BR Br bR br BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr Dihybrid Crosses:a cross that shows the possible offspring for two traits BbRr x BbRr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

  7. BR Br bR br BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr How many of the offspring would have a black, rough coat? How many of the offspring would have a black, smooth coat? How many of the offspring would have a white, rough coat? How many of the offspring would have a white, smooth coat? Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

  8. BR Br bR br BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr How many of the offspring would have black, rough coat? How many of the offspring would have a black, smooth coat? How many of the offspring would have a white, rough coat? How many of the offspring would have a white, smooth coat? Phenotypic Ratio= 9:3:3:1 Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

  9. Practice in your notes… In pea plants, yellow seeds (Y) are dominant over green seeds (y), and rounded peas (R) are dominant over wrinkled peas (r). Cross (what do you have to draw?) a plant that is heterozygous for both traits with a plant that is homozygous recessive for both traits. Draw a Punnett square to show all possible offspring, and determine the genotypic and phenotypic ratios.

  10. YR Yr yR yr yr YyRr Yyrr yyRr yyrr yr YyRr Yyrr yyRr yyrr yr YyRr Yyrr yyRr yyrr yr YyRr Yyrr yyRr yyrr YyRr X yyrr

  11. More Practice • Work on the SpongeBob Dihybrid Cross worksheet. Turn it in at the end of class.

  12. Mendelian Genetics ReviewGet with a partner.Walk around the room and answer the review questions with your partner.If you get all the answers correct, you will get 1 extra point on your quiz!

  13. What is a genotype? The genes (letters) that determine a phenotype • A man is heterozygous for a trait. Will the dominant or recessive trait be expressed? Why? Dominant because dominant covers recessive • What does it mean if a woman is homozygous recessive? Using the letter “B,” write her genotype. Both of her genes are recessive (bb) • What is a phenotype? The physical characteristics of an organism

  14. Long eyelashes (E) are dominant to short eyelashes (e). A heterozygous woman is crossed with a homozygous man. What is the percent chance their offspring will have short eyelashes? (Must draw a Punnett square) 0% (see board) • The offspring of two parents has a 100% chance of being homozygous recessive for blue eyes. If this is the case, what must the genotype be for both parents? bb • What does homozygous mean? Write an example. Homozygous means the same letters are present Ex. BB or bb

  15. What does heterozygous mean? Write an example. That the genes are different Ex. Bb • What does it mean if a gene is expressed? The phenotype for that gene is seen (dominant) • What does a dihybrid cross show? Genetic possibilities for 2 traits • What was Mendel’s predicted genotypic ratio for a typical dihybrid cross? 9:3:3:1 • Hazel eyes (H) are dominant to green eyes (h). A homozygous dominant man is crossed with a homozygous woman. What is the percent chance their offspring will have green eyes? (Must draw a Punnett square!) 100% (see board)

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