Genetics and DNA: The Science of Heredity Ms. De Los Rios 7th Grade 12-2 What Is Heredity?

Vocabulary Heredity- The passing of traits from parents to offspring. Genetics- The scientific study of heredity. Fertilization- The process in sexual reproduction in which an egg cell and a sperm cell join to form a new cell. Purebred- An offspring of many generations that have the same form of trait. Alleles- The different forms of a gene.

Vocabulary Dominant allele- An allele whose trait always shows up in the organism when the allele is present. Recessive allele- An allele that is hidden whenever the dominant allele is present. Hybrid- An offspring of crosses that has two different alleles for a trait.

My Planet Diary pg. 414 Almost Forgotten- When scientists make great discoveries, sometimes their work is praised, criticized, or even forgotten. Gregor Mendel was almost forgotten. He spent eight years studying pea plants, and he discovered patterns in the way characteristics pass from one generation to the next. For almost 40 years, people overlooked Mendel’s work. When it was finally rediscovered, it unlocked the key to understanding heredity. Did you ever rediscover something of yours That you had forgotten? How did you react? _____________________________________

What Did Mendel Observe? Pg. 414 In the mid-nineteenth century, Gregor Mendel wondered why pea plants had different characteristics. Each characteristic, such as height or seed color, is called a trait. Mendel wondered why the forms of the pea plants’ traits were often—but not always—similar to their parents. His discoveries form the foundation of genetics, the study of heredity. Heredity- How traits are passed from parents to offspring.

Mendel’s Experiments pg. 415 In a pea plant flower, the pistil produces female sex cells, or eggs. The stamens produce pollen, which contains the male sex cells, or sperm. A new organism begins to form when egg and sperm cells join, a process called fertilization. For this to occur in plants, pollen must reach the pistil of a flower, a process called pollination. Pea plants usually self-pollinate: Pollen from a flower lands on the pistil of the same flower.

Mendel’s Experiments figure 2 -pg. 415 Crossing Pea Plants Mendel devised a way to cross-pollinate pea plants. Observe- How does flower B differ from flower A? ___________________________ Infer- Describe how Mendel cross-pollinated pea plants. _____________________ _____________________________________________________________________

F1 and F2 Offspring pg. 416 A purebred organism is the offspring of many generations that have the same form of a trait. Mendel cross-pollinated, or “crossed,” purebred tall with purebred short plants. Scientists call these the parental, or P, generation. The offspring of the P generation are called the first filial, or F1, generation. Their offspring are called the second filial, or F2, generation.

In all of his crosses, Mendel found that 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. Results of a Cross In Mendel’s crosses, some forms of a trait were hidden in one generation but reappeared in the next. What was surprising about the offspring in the F2 generation? Draw and label the offspring in the F2 generation.

Assess Your Understanding pg. 416 1a. Explain- The passage of traits from one generation to the next generation is called ____________________________________. b. Compare and Contrast- In Mendel’s cross for stem height, how did the plants in the F2 generation differ form the F1 plants? _________ _______________________________________________________ I get it! Now I know that Mendel found that one form of a trait ______________________________________________________________________________________________________________

How Do Alleles Affect Inheritance? Pg. 417 Today, scientists use the word gene to describe the factors that control a trait. Alleles are the different forms of a gene. The gene that controls stem height in peas has one allele for short stems and one allele for long stems. An organism’s traits are controlled by the alleles it inherits from its parents. Some alleles are dominant – strong traits that overpower weak traits. Dominant alleles are symbolized with capital letters. while other alleles are recessive- weak traits that are hidden whenever the dominant allele is present. Recessive alleles are symbolized by lowercase letters

Alleles in Pea Plants Mendel studied the inheritance of seven different traits in pea plants. Draw Conclusions- Circle the picture of the dominant allele in the P generation for each trait. Predict- Under what conditions would the recessive form of one of these traits reappear? ______________________________________________________

Alleles in Mendel’s Crosses pg. 418 In Mendel’s cross for stem height, the purebred tall plants in the P generation had two alleles for tall stems. TT The purebred short plants had two alleles for short stems. Tt But…. Each F1 plant inherited one allele for tall stems and one allele for short stems. Tt - These plants are called hybrids All of these F1 plants are tall because the dominant allele T overpowers the recessive allele t . Purebred – TT or tt Hybrid - Tt

Dominant and Recessive Alleles Pg. 418 1.What are the symbols and descriptions of allele? 2.Use the word bank to complete the statements. 3.What are the two possible ways the F2 offspring could look?

Apply it! Pg. 419 In fruit flies, long wings are dominant over short wings. A scientist crossed a purebred long-winged fruit fly with a purebred short-winged fruit fly. If W stands for long wings, write the symbols for the alleles of each parent fly.______________________________________ Predict- What will be the wing length of the F1 offspring? Predict- If the scientist crosses a hybrid male F1 fruit fly with a hybrid F2 female, what will their offspring probably be like? ________________________________________________________________________________________________

Assess Your Understanding pg. 419 2a. Identify- How did Mendel’s work change scientific knowledge about genetics? _________________________________________________________ _________________________________________________________ b. Relate Cause and Effect- Why is a pea plant tall when it is a hybrid for stem height? ______________________________________ ___________________________________________________ I get it! Now I know that an organism’s traits are controlled by __________________________________________________________________________________________________________________