Transcript Slide 1
Lesson 18 Using Punnett Squares and Pedigrees Bb x Bb male / sperm X B b BB Bb Bb bb female / eggs B b 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. The couple comes to you for counseling. They want you to know the chances they will have a healthy baby. 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 Man x Woman Rr r Rrr R ? R RR Rr r Rr rr R Man x Woman Rr r Rr Genotype % RR = 25% Rr = 50% rr = 25% Phenotype % Healthy = 25% Carrier = 50% Diseased = 25% Let’s Practice! R RR Rr r Rr rr The chance that the couple will have a baby that has the disease is 25%. HUNTINGTON’S DISEASE: dominantly inherited disease A man has Huntington’s disease. He Man x Woman does not know this because Huntington’s doesn’t show symptoms until later in life, Rr rr after children have been produced. 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 Rr rr r Rr rr 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 AB Tall/Brown Tall/blond AB Short/Brown Ab Short/blond aB ab Ab aB ab Testcross unknown 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. But I do not know my genetics. How can I know if my beebies will be red? R? rr Maybe I can help you with a testcross! www.zamzows.com www.vetnetwork.net static.howstuffworks.com 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? www.vetnetwork.net rr If you get any homozygous recessive babies, you www.zamzows.com know you carry the recessivestatic.howstuffworks.com gene! Congratulations handsome! ‘Eeet worked! Rr R? Now I know that I carry the rare white gene! rr You’re a carrier! www.zamzows.com static.howstuffworks.com www.vetnetwork.net Later that year the babies were born… Rr animal-world.com Rr www.sandsexoticanimals.com The twins Rr and Rr aaawebmaster.com rr www.stuff4birds.com Rr I’m the jailbird. www.lorislittlecritters.com What would be the genotype needed to testcross a heterozygous purple-flowering pea plant? a. PP b. Pp c. pp 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. Why are most sex-linked traits carried on the X chromosome? Female must get two (XX) X’s to have colorblindness. Male must get one (XY) X to have colorblindness. Reading a Pedigree = male without trait = female without trait = male with trait = female with trait = male carrier = female carrier I II = two parents = three children Analyzing a Pedigree Interactive http://highered.mcgraw-hill.com/sites/0072485949/student_view0/chapter3/interactive_activity.html Remember this? Let’s Practice! Any Questions? blogs.reuters.com farm1.static.flickr.com Assignment: Coach Book L18 Textbook pg 201 Read and Summarize cdn.24.com These people all have Down’s Syndrome www.thejakartapost.com