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

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

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

5. 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. Data Sharing Lab - Mendel’s Work
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. Percentages - Probability and Heredity
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%

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

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

14. What Are the Genotypes? - Probability and Heredity 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.
8,000; 75% have yellow peas and 25% have green peas.

15. What Are the Genotypes? - Probability and Heredity 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.)
Both parents probably had the genotype Bb.

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

18. Building Vocabulary - Probability and Heredity
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:
homozygous
heterozygous
codominance
Key Terms:
Examples:
probability
An organisms that has two identical alleles for a trait is said to be homozygous.
Probability is a number that describes how likely it is that an event will occur.
Punnett square
An organisms that has two different alleles for a trait is heterozygous for that trait.
A Punnett square is a chart that shows all the possible combinations of alleles that can result from a genetic cross.
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. Links on Probability and Genetics
- 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. Meiosis - The Cell and Inheritance
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. Punnett Square - The Cell and Inheritance
A Punnett square is actually a way to show the events that occur at meiosis.

23. A Lineup of Genes - The Cell and Inheritance
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. Identifying Supporting Evidence
- 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 has 24 chromosomes.
Alleles exist in pairs in organisms.

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

26. Click the Video button to watch a movie about chromosomes.
- 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 Code - The DNA Connection
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. How Cells Make Proteins
- 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. Protein Synthesis Activity
- The DNA Connection
Protein Synthesis Activity
Click the Active Art button to open a browser window and access Active Art about protein synthesis.

31. Mutations - The DNA Connection
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. Sequencing - The DNA Connection
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. Click the Video button to watch a movie about protein synthesis.
- The DNA Connection
Protein Synthesis
Click the Video button to watch a movie about protein synthesis.

34. End of Section: The DNA Connection

35. Graphic Organizer RNA Messenger RNA Transfer RNA includes 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