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

Genetics: The Science of Heredity - Mendel’s Work Mendel’s Experiments In all of Mendel’s crosses, only one form of the trait appeared in the F 1 generation. However, in the F 2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants.

Genetics: The Science of Heredity - Mendel’s Work Dominant and Recessive Alleles Mendel studied several traits in pea plants.

Genetics: The Science of Heredity Percentages 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. 1. 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

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

Genetics: The Science of Heredity - 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.

Genetics: The Science of Heredity - 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.

Genetics: The Science of Heredity What Are the Genotypes? Mendel allowed several F 1 pea plants with yellow seeds to self- pollinate. The graph shows the approximate numbers of the F 2 offspring with yellow seeds and with green seeds. - Probability and Heredity

Genetics: The Science of Heredity What Are the Genotypes? Yellow–6,000; green–2,000 Reading Graphs: How many F 2 offspring had yellow seeds? How many had green seeds? - Probability and Heredity

Genetics: The Science of Heredity What Are the Genotypes? 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

Genetics: The Science of Heredity What Are the Genotypes? 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

Genetics: The Science of Heredity - 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.

Genetics: The Science of Heredity - Probability and Heredity Codominance In codominance, the alleles are neither dominant nor recessive. As a result, both alleles are expressed in the offspring.

Genetics: The Science of Heredity - 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.

Genetics: The Science of Heredity - The Cell and Inheritance Punnett Square A Punnett square is actually a way to show the events that occur at meiosis.

Genetics: The Science of Heredity - 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.

Genetics: The Science of Heredity 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. Chromosomes are important in inheritance. Grasshoppers: 24 chromosomes in body cells, 12 in sex cells. Fertilized egg has 24 chromosomes. Alleles exist in pairs in organisms. - The Cell and Inheritance

Genetics: The Science of Heredity Chromosomes Click the Video button to watch a movie about chromosomes. - The Cell and Inheritance

Genetics: The Science of Heredity - 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.

Genetics: The Science of Heredity - 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.

Genetics: The Science of Heredity - 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.

Genetics: The Science of Heredity 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. - The DNA Connection

Genetics: The Science of Heredity Protein Synthesis Click the Video button to watch a movie about protein synthesis. - The DNA Connection

Genetics: The Science of Heredity Graphic Organizer Transfer RNA RNA Messenger RNA includes Carry amino acids 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