Gene Squares 1-31-14 Do Now Gene Squares Key Question: How can you predict the probability of traits appearing? 4 minutes Initial Thoughts: Evidence – Punnett Squares Step by Step 1. Write the possible alleles donated by each parent along the top and left side of the table? Skye *Each T along the top represents an allele in the sperm cell produced by Skye. Each t on the left represents an allele in the egg cell from Poppy. TT T Poppy t tt t T Evidence – Punnett Squares Step by Step 2. Complete each box of the table by combining one allele from the top and one allele from Skye the left. TT * When you combine one allele from each parent into a box, you are representing a sperm cell fertilizing an egg. T Poppy t tt t T Evidence – Punnett Squares Step by Step 3. Now you can use the Punnett square to make some conclusions. *All of the offspring of Skye and Poppy will have one allele for blue tail color and one allele for orange tail color. Their genotypes will be Tt. An organism that has alleles for two different traits is called heterozygous. Because blue tail color is dominant over orange, the phenotype of all offspring is blue tails, as found in the breeding experiment between Skye and Poppy. Evidence – Punnett Squares The cross between the Generation 2 (Tt) critters Ocean and Lucy is: Ocean X Lucy Tt X Tt T = allele for blue tail color (dominant) t = allele for orange tail color (recessive) *Note that while Ocean and Lucy both have blue tails, they are both heterozygous. Evidence – Punnett Squares 1. Complete this Punnett square for the cross between Ocean and Lucy? Ocean a. Place Ocean’s and Lucy’s alleles on the dotted lined in the Punnett square. b. Complete the Punnett square by filling in each box with the allele above it and the allele to its left. Tt ----Lucy ----- Tt ----- ----- Evidence – Punnett Squares c. Use either a blue pencil or a regular pencil to shade in the squares for offspring that will have blue tails in your Punnett square. d. About what fraction of the offspring of Ocean and Lucy are predicted to have blue tails, according to the Punnett square? e. About what fraction are predicted to have orange tails? Evidence: Punnett Squares • Paste the punnett square practice problems into your notebook. Analysis Questions 1. Why is it impossible for offspring to show the recessive trait if one parent is homozygous for the dominant trait? 2. What is the probability of having a boy (xy) vs. a girl (xx)? Dad x x Mom x y Analysis Questions contd. 3. A scientist has some purple-flowered pea plants. She wants to find out if the pea plants are homozygous dominant for the purple flower color. White is recessive. Use P = purple p = white. a) What cross will be best to find out if the purpleflowered peas are homozygous? b) Use Punnett squares to show what will happen if the plants are crossed with white-flowered plants and i. the purple-flowered plants do not have an allele for the white trait. ii. the purple-flowered plants do have an allele for the white trait. Summary • What did you think about predicting the probability of traits before? • What did you learn from your evidence about predicting the probability of traits? • What are some further thoughts or questions you have about predicting the probability of traits? Reflection • How can you tell if a flower is homozygous dominant? What experiment can you do? Big Idea • Punnett squares can be used to predict the probabilities of certain dominant and recessive traits.