Table of Contents

1. Table of Contents • Mendel’s Work • Probability and Heredity • The Cell and Inheritance • The DNA Connection

2. - Mendel’s Work Crossing Pea Plants • Gregor Mendel crossed pea plants that had different traits. The illustrations show how he did this.

3. - Mendel’s Work Mendel’s Experiments • In all of Mendel’s crosses, only one form of the trait appeared in the F1 generation. However, in the F2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants.

4. - Mendel’s Work Dominant and Recessive Alleles • Mendel studied several traits in pea plants.

5. - Mendel’s Work Outlining Mendel’s Work • As you read, make an outline about Mendel’s work. Use the red headings for the main ideas and the blue headings for the supporting ideas. • Mendel’s Experiments • Crossing Pea Plants • The F1 Offspring • The F2 Offspring • Experiments With Other Traits • Dominant and Recessive Alleles • Genes and Alleles • Alleles in Mendel’s Crosses • Symbols for Alleles • Significance of Mendel’s Contribution

6. - Mendel’s Work Data Sharing Lab • Click the PHSchool.com button for an activity about sharing data for the Skills Lab Take a Class Survey.

7. End of Section:Mendel’s Work

8. One way you can express a probability is as a percentage. A percentage (%) is a number compared to 100. For example, 50% means 50 out of 100. Suppose that 3 out of 5 tossed coins landed with heads up. Here’s how you can calculate what percent of the coins landed with heads up. Write the comparison as a fraction. 3 out of 5 = 3/5 2. Multiply the fraction by 100% to express it as a percentage. 3/5 x 100%/1 = 60% - Probability and Heredity Percentages

9. Practice Problem Suppose 3 out of 12 coins landed with tails up. How can you express this as a percent? 25% - Probability and Heredity Percentages

10. - Probability and Heredity A Punnett Square • The diagrams show how to make a Punnett square. In this cross, both parents are heterozygous for the trait of seed shape. R represents the dominant round allele, and r represents the recessive wrinkled allele.

11. - Probability and Heredity Probability and Genetics • In a genetic cross, the allele that each parent will pass on to its offspring is based on probability.

12. - Probability and Heredity What Are the Genotypes? • Mendel allowed several F1 pea plants with yellow seeds to self-pollinate. The graph shows the approximate numbers of the F2 offspring with yellow seeds and with green seeds.

13. Yellow–6,000; green–2,000 Reading Graphs: How many F2 offspring had yellow seeds? How many had green seeds? - Probability and Heredity What Are the Genotypes?

14. 8,000; 75% have yellow peas and 25% have green peas. Calculating: Use the information in the graph to calculate the total number of offspring that resulted from this cross. Then calculate the percentage of the offspring with yellow peas, and the percentage with green peas. - Probability and Heredity What Are the Genotypes?

15. Both parents probably had the genotype Bb. Inferring: Use the answers to Question 2 to infer the probable genotypes of the parent plants. (Hint: Construct Punnett squares with the possible genotypes of the parents.) - Probability and Heredity What Are the Genotypes?

16. - Probability and Heredity Phenotypes and Genotypes • An organism’s phenotype is its physical appearance, or visible traits, and an organism’s genotype is its genetic makeup, or allele combinations.

17. - Probability and Heredity Codominance • In codominance, the alleles are neither dominant nor recessive. As a result, both alleles are expressed in the offspring.

18. Key Terms: Examples: homozygous heterozygous codominance - Probability and Heredity Building Vocabulary • After you read the section, reread the paragraphs that contain definitions of Key Terms. Use all the information you have learned to write a definition of each Key Term in your own words. Key Terms: Examples: probability Probability is a number that describes how likely it is that an event will occur. An organisms that has two identical alleles for a trait is said to be homozygous. Punnett square A Punnett square is a chart that shows all the possible combinations of alleles that can result from a genetic cross. An organisms that has two different alleles for a trait is heterozygous for that trait. In codominance, the alleles are neither dominant nor recessive. phenotype An organism’s phenotype is its physical appearance, or visible traits. genotype An organism’s genotype is its genetic makeup, or allele combinations.

19. - Probability and Heredity Links on Probability and Genetics • Click the SciLinks button for links on probability and genetics.

20. End of Section:Probability and Heredity

21. - The Cell and Inheritance Meiosis • During meiosis, the chromosome pairs separate and are distributed to two different cells. The resulting sex cells have only half as many chromosomes as the other cells in the organism.

22. - The Cell and Inheritance Punnett Square • A Punnett square is actually a way to show the events that occur at meiosis.

23. - The Cell and Inheritance A Lineup of Genes • Chromosomes are made up of many genes joined together like beads on a string. The chromosomes in a pair may have different alleles for some genes and the same allele for others.

24. - The Cell and Inheritance Identifying Supporting Evidence • As you read, identify the evidence that supports the hypothesis that genes are found on chromosomes. Write • the evidence in a graphic organizer. Grasshoppers: 24 chromosomes in body cells, 12 in sex cells. Chromosomes are important in inheritance. Fertilized egg has24 chromosomes. Alleles exist in pairs in organisms.

25. - The Cell and Inheritance Links on Meiosis • Click the SciLinks button for links on meiosis.

26. - The Cell and Inheritance Chromosomes • Click the Video button to watch a movie about chromosomes.

27. End of Section:The Cell and Inheritance

28. - The DNA Connection The DNA Code • Chromosomes are made of DNA. Each chromosome contains thousands of genes. The sequence of bases in a gene forms a code that tells the cell what protein to produce.

29. - The DNA Connection How Cells Make Proteins • During protein synthesis, the cell uses information from a gene on a chromosome to produce a specific protein.

30. - The DNA Connection Protein Synthesis Activity • Click the Active Art button to open a browser window and access Active Art about protein synthesis.

31. - The DNA Connection Mutations • Mutations can cause a cell to produce an incorrect protein during protein synthesis. As a result, the organism’s trait, or phenotype, may be different from what it normally would have been.

32. - The DNA Connection Sequencing • Sequence is the order in which the steps in a process occur. As you read, make a flowchart that shows protein synthesis. Put each step in the flowchart in the order in which it occurs. Protein Synthesis DNA provides code to form messenger RNA. Messenger RNA attaches to ribosome. Transfer RNA “reads” the messenger RNA. Amino acids are added to the growing protein.

33. - The DNA Connection Protein Synthesis • Click the Video button to watch a movieabout protein synthesis.

34. End of Section:The DNA Connection

35. Graphic Organizer RNA includes Transfer RNA Messenger RNA functions to functions to Copy the coded message from the DNA Carry the message to the ribosome in the cytoplasm Add amino acids to the growing protein Carry amino acids

36. End of Section:Graphic Organizer