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Lesson 18 Using Punnett Squares and Pedigrees

B. b. B. b. Lesson 18 Using Punnett Squares and Pedigrees. Bb x Bb. male / sperm. X. BB. B b. Remember this?. female / eggs. B b. bb. A Punnett Square is a diagram used to identify possible combinations resulting from a mating.

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Lesson 18 Using Punnett Squares and Pedigrees

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  1. B b B b Lesson 18 Using Punnett Squares and Pedigrees Bb x Bb male / sperm X BB Bb Remember this? female / eggs Bb bb

  2. A Punnett Square is a diagram used to identify possible combinations resulting from a mating. This married couple is considering having their first baby. The man is heterozygous for a disease. The woman is also heterozygous for the disease.

  3. The couple comes to you for counseling. They want you to know the chances they will have a healthy baby.

  4. You know that the disease they carry is a recessive trait and that both parents are heterozygous. RR Rr rr Which of the above genotypes will you need to use? R r Man x Woman Rr R r Rr R r R R R r R ? r R r r r

  5. R r Man x Woman Rr Rr R R R r R Genotype % RR = Rr = rr = 25% 50% r R r r r 25% Phenotype % Healthy = Carrier = Diseased = 25% 50% The chance that the couple will have a baby that has the disease is 25%. 25% Let’s Practice!

  6. HUNTINGTON’S DISEASE: dominantly inherited disease A man has Huntington’s disease. He does not know this because Huntington’s doesn’t show symptoms until later in life, after children have been produced. Man x Woman Rr rr His wife does not have Huntington’s and knows that it has never been diagnosed in her family pedigree. What are the chances their first born child will have the disease? R r R r r r r r R r r r

  7. Dihybrid Crosses = mating of two individuals involving two traits. A = tall a = short B = brown hair b = blond hair Heterozygous for both traits: AaBb x AaBb Tall/Brown Tall/blond Short/Brown Short/blond 9:3:3:1

  8. Testcrossunknown x aa ‘ello, my name is Reginald. I am a magnificent red canary. Hi there handsome! My name’s Gloria and I’m a purely recessive white gal. I want to make ‘de beautiful red beebies like me. Maybe I can help you with a testcross! But I do not know my genetics. How can I know if my beebies will be red? R? rr www.vetnetwork.net www.zamzows.com static.howstuffworks.com

  9. TESTCROSS = a cross between any gene pair and the homozygous recessive condition for that trait. It’s when you cross an unknown genotype with a homozygous recessive. ‘Dees TESTCROSS…What is it? Hmm… I think this TESTCROSS is a good idea. R? rr If you get any homozygous recessive babies, you know you carry the recessive gene! www.zamzows.com www.vetnetwork.net static.howstuffworks.com

  10. Congratulations handsome! ‘Eeet worked! Now I know that I carry the rare white gene! Rr R? R? rr You’re a carrier! animal-world.com www.zamzows.com Later that year the babies were born… The twinsRr and Rr rr Rr Rr Rr I’m the jailbird. www.vetnetwork.net static.howstuffworks.com www.lorislittlecritters.com www.sandsexoticanimals.com aaawebmaster.com www.stuff4birds.com

  11. What would be the genotype needed to testcross a heterozygous purple-flowering pea plant? a. PP b. Pp c. pp

  12. Pedigree = family record for one specific trait. Sex-linked traits = genes for these traits are carried on the sex chromosomes. The gene for Red-Green colorblindness is carried on the X chromosome. Female must get two (XX) X’s to have colorblindness. Why are most sex-linked traits carried on the X chromosome? Male must get one (XY) X to have colorblindness.

  13. Reading a Pedigree = female without trait = male without trait = female with trait = male with trait = male carrier = female carrier = two parents I II = three children Analyzing a Pedigree Interactive http://highered.mcgraw-hill.com/sites/0072485949/student_view0/chapter3/interactive_activity.html

  14. Remember this?

  15. Another view of a pedigree… This one is for Huntington’s Disease Let’s Practice!

  16. Any Questions? blogs.reuters.com farm1.static.flickr.com Assignment: Coach Book L18 Textbook pg 201 Read and Summarize These people all have Down’s Syndrome cdn.24.com www.thejakartapost.com

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