Day 15: Genetics. Insert Do Now

Transcription

1 Insert Do Now

2 Guided Notes: Genetics and Punnet Squares 1. What is a purebred? (slide 1) 2. What are the two purebreds in this example? (slide 1) 3. What does dominant mean? (slide 1) 4. What is a phenotype? (slide 1) 5. What are the two phenotypes in this example? (slide 1) 6. What is a gene? (slide 3) 7. What is an allele? (slide 3) 8. What are the two alleles in this example? (slide 3) 9. What does it mean to be homozygous? (slide 4) 10. What does it mean to be heterozygous? (slide 7) 11. What is the dominant allele? (slide 8) Punnett Squares 1. What is a gamete? (slide 3)

3 2. What is a genotype (slide 7) 3. What are the three genotypes represented in this example? (slide 7) 4. Which genotypes will produce yellow plants? (slide 11) 5. Which genotypes will produce green plants? (slide 11)

4 How to Use a Punnet Square to complete a Monohybrid Cross Problem In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds? The figure above represents a monohybrid cross of F1-hybrid plants. Both parent plants are heterozygous (Ss) for an allele that determines seed shape. Presence of the dominant allele (S) in homozygous (SS) or heterozygous (Ss) plants results in showing the dominant trait, or spherical seeds. Homozygous recessive (ss) plants have dented seeds. To solve this problem, you'll need to set up a Punnett square. This tutorial will walk you through that process. Setting up a Punnett square 1. Write the given. Look at the word problem. Identify the (1) trait, (2) dominant and recessive forms of the trait by using a capital or lowercase letter, (3) genotype and phenotype of the parent plants. Trait: Pea Shapes Dominant: S= Spherical Recessive: s= dented Parents: Ss (spherical) x Ss (spherical) 2. Set up a 2 by 2 Punnett square. 3. Write the alleles from parent 1 above the Punnett square. For this heterozygous parent (Ss), half of the gametes will have the dominant (S) allele, and half will have the recessive (s) allele. Repeat for parent 2 on the left side of the punnet square. 4. Fill the squares: Bring down and move across Fill each square with the allele (letter) from Parent 1 and 2 that lines up with the row and column.

5 5. Interpret Results After the square is filled in, write down the type of genotypes the offspring may have. (see a) Look at whether it is homozygous dominant, homozygous recessive or heterozygous. For more challenging problems, convert the genotype to phenotype. What do the different letters mean in terms of physical traits? Interpreting the results of a Punnett square We now have the information for predicting the outcome of the cross. The genotypes in the four boxes of the Punnett square are each equally likely to occur among the offspring of this cross. We may now tabulate the results. Genotypes that resulted from this monohybrid cross (Ss x Ss) 25% homozygous dominant 50% heterozygous 25% homozygous recessive Answer the following questions and show your work: What percentage of the plants are homozygous dominant? What percentage of the plants are heterozygous dominant? What percentage of the plants are spherical? What percentage of the plants are homozygous recessive? Phenotypes that resulted from this monohybrid cross (Ss x Ss)

6 Genetics-Practice Problems 1. For each genotype below, indicate whether it is heterozygous (He) or homozygous (Ho) AA Ee Ii Mm Bb ff Jj nn 2. For each phenotype below, list the genotypes (remember to use the letter of the dominant trait) Straight hair is dominant to curly. straight straight curly Pointed heads are dominant to round heads. pointed pointed round 3. Set up the Punnett squares for each of the crosses listed below. Round seeds are dominant to wrinkled seeds. RR x rr What percentage of the offspring will be round? Rr x Rr What percentage of the offspring will be round? Practice with Crosses. Show all work! 4. A TT (tall) plant is crossed with a tt (short plant). SHOW ALL WORK! 4. What percentage of the offspring will be tall? 5.

7 5. A Tt plant is crossed with a Tt plant. What percentage of the offspring will be short? 6. A heterozygous round seeded plant (Rr) is crossed with a homozygous round seeded plant (RR). 6. What percentage of the offspring will be homozygous (RR)? 7. A homozygous round seeded plant is crossed with a homozygous wrinkled seeded plant. 7. What are the genotypes of the parents? x What percentage of the offspring will also be homozygous? 8. In pea plants purple flowers are dominant to white flowers. 8. If two white flowered plants are cross, what percentage of their offspring will be white flowered? 9.

8 9. A white flowered plant crossed with a plant that is heterozygous for the trait. What percentage of the offspring will have purple flowers? 10. Two plants, both heterozygous for the gene that controls flower color are crossed. 10. What percentage of their offspring will have purple flowers? What percentage will have white flowers? Homework: Genetics-Practice Problems II 1. For each genotype below, indicate whether it is heterozygous (He) or homozygous (Ho) Cc Gg kk oo DD HH LL Pp 2. Set up the Punnett squares for each of the crosses listed below. Round seeds are dominant to wrinkled seeds. Rr x rr What percentage of the offspring will be round? RR x Rr What percentage of the offspring will be round? Practice with Crosses. Show all work! SHOW ALL WORK! 3. In guinea pigs, the allele for short hair is dominant. What genotype would a heterozygous short haired guinea pig have?

9 What genotype would a purebred short haired guinea pig have? What genotype would a long haired guinea pig have? 4. Show the cross for a pure breeding short haired guinea pig and a long haired guinea pig. What percentage of the offspring will have short hair? 5. Show the cross for two heterozygous guinea pigs. What percentage of the offspring will have short hair? What percentage of the offspring will have long hair? 6. Two short haired guinea pigs are mated several times. Out of 100 offspring, 25 of them have long hair. What are the probable genotypes of the parents? x Show the cross to prove it! SAT Challenge Problem: Super Challenging: Take an Extra Challenge! You are a part of a special secret committee working with Captain Veggie and the Breakthrough New York Food Project. Their goal is to develop a tastier apple so BT students are more likely to eat their fruits and vegetable. Your job is to help Captain Veggie breed a tastier apple through artificial selection. Artificial selection is This means scientists can control what the offspring may look like or have certain traits. For ex: If Mendel wanted all yellow plants, he purposely crossed 2 homozygous dominant yellow plants. Which of the following apple traits would be easier to eliminate through artificial selection: a dominant allele for bitterness (B) or recessive allele for mushy texture (b). Show your logic and explain why. You may want to use a punnet square and think about Mendel s plant experiments to work through the logic.