Definition/Example Signature

Transcription

1 Engage: Who Remembers? Instructions: Discuss the following terms with other students. Try to find someone who can explain the term to you or give you an example of the term. Record the definition or example on this sheet. Have that person sign your sheet. You may only receive one answer from each person. Term Definition/Example Signature Homozygous Heterozygous Dominant Recessive Genotype Phenotype Trait

2 Explore: How to Solve a Monohybrid Cross Lesson 4 Background: Your team has been assigned the task of teaching new biology students how to solve a monohybrid cross. The problem is written for you below. Work together as a group to develop steps that students should follow to complete the cross. Make sure to explain the probabilities for each genotype and phenotype. Complete the chart below once you have decided on your sequence. Problem: In humans, free earlobes are dominant to attached earlobes. One parent is homozygous recessive for attached earlobes and the other parent is heterozygous for free earlobes. If the couple has 12 children, predict how many children will have attached earlobes and how many children will have free earlobes. First Steps to a Monohybrid Cross Second Third Fourth Fifth

3 Explain: Punnett Squares and Genetics Lesson 4 Part 1: Incomplete Dominance Inheritance known as incomplete dominance occurs when one allele is not completely dominant over the other allele. The heterozygous phenotype is a blend of the two traits. For example, in snapdragon flowers, red flowers are not completely dominant over white flowers. This means when a pure red and a pure white flower are crossed, the heterozygous offspring produces a pink flower. Complete the practice problem: What are the genotypic and phenotypic ratios when you cross a red snapdragon with a pink snapdragon? Part 2: Codominance In a codominant inheritance, both alleles are dominant. This means that in the heterozygous individual, both alleles are expressed. For example, in cattle, a white hair bull (WW) crossed with a red hair cow (RR) results in a roan calf (RW). A roan coat contains both red and white hair. Complete the practice problem: Erminette chickens are chickens with feathers that are both white and black. Chickens may have black feathers, white feathers, or black and white feathers. What are the genotypic and phenotypic ratios when you cross two erminette chickens?

4 Part 3: Multiple Alleles Some genes have more than two alleles that affect the trait. For example, in humans, blood type is affected by three different alleles: A, B, and O. These three alleles result in four different phenotypes for blood type: A, B, AB, and O. Blood Group Phenotypes A B AB O Possible Genotypes Complete the practice problem: A woman with Type O blood and a man with Type AB blood have a baby. Could a child with Type O blood belong to the parents? Part 4: Dihybrid Cross (Mendelian Genetics) A dihybrid cross is used to predict the outcome of a cross involving two traits. In a dihybrid cross, there are two genes and four alleles, such as RrWw, for each organism. Each of the alleles separates during meiosis, creating four possible combinations in each gamete, or sex cell: RW, Rw, rw, rw. The Punnett square must contain 16 boxes. Complete the practice problem: (You will work on this problem at Stations 4 and 5.) Fruit flies exist in many forms. In fruit flies, wings (W) are dominant to no wings (w). Red eyes (R) are dominant to white eyes (r). Cross a heterozygous winged and homozygous red-eyed fruit fly with a wingless white-eyed fruit fly. STAAR Achievement Series for Science 2013 Region 4 Education Service Center

5 Part 5: Dihybrid Cross (Mendelian Genetics) A dihybrid cross is used to predict the outcome of a cross involving two traits. In a dihybrid cross, there are two genes and four alleles, such as RrWw, for each organism. Each of the alleles separates during meiosis, creating four possible combinations in each gamete, or sex cell: RW, Rw, rw, rw. The Punnett square must contain 16 boxes. Complete the practice problem: (You will work on this problem at Stations 4 and 5.) Fruit flies exist in many forms. In fruit flies, wings (W) are dominant to no wings (w). Red eyes (R) are dominant to white eyes (r). Cross a heterozygous winged and homozygous red-eyed fruit fly with a wingless white-eyed fruit fly. Part 6: Monohybrid Cross (Mendelian Genetics) Gregor Mendel is often referred to as the father of genetics as a result of his work with inheritance patterns. Mendel tested his theories of inheritance using pea plants. Monohybrid crosses were used to investigate the inheritance of a single trait. Mendel noticed that some traits were dominant over other traits. He also noticed that the recessive traits can only be expressed when the organism is homozygous recessive for the trait. Complete the practice problem: Mendel cut the pollen-producing male parts from both flowers of the pea plant. He then dusted the female parts with the pollen from different plants. Tall plants are dominant to short plants. Cross two heterozygous tall pea plants. When you finish your Punnett square, compare your results with the results Mendel observed. Mendel observed 787 tall plants and 277 short plants. Do his results match the results you predicted? Why or why not?

6 Elaborate: You Are Hired Lesson 4 Background information: December 23, 1972, was the first day of work for a young nurse. It was an unusually busy night at the hospital and four beautiful babies were born. Five years later, Mr. and Mrs. Williams were involved in a car accident. Their son, John, was injured but later made a full recovery. The night of the accident, Mr. and Mrs. Williams both volunteered to donate blood. The news they received was devastating. Neither of them was a match and they could not donate blood. This meant John was not their biological son. You have been hired by the Williams to locate their biological son. In an interview with Mr. and Mrs. Williams, you ask several important questions and make a few key observations. Through research, you learn that hair texture is controlled by incomplete dominance. Individuals who are homozygous dominant for hair texture have curly hair (CC). Individuals who are homozygous recessive have straight hair (cc). Individuals who are heterozygous have wavy hair (Cc). After reviewing your notes, you decide to concentrate on two key pieces of information: Mr. Williams is heterozygous for Type B blood and has wavy hair. Mrs. Williams is homozygous for Type A blood and has straight hair. The hospital records contain important information about the other children who were born in the hospital that day: Baby 1 is heterozygous for Type B blood and has wavy hair. Baby 2 has Type AB blood and has straight hair. Baby 3 is heterozygous for Type A blood and has curly hair. Your instructions: Work with your team to determine which baby is Mr. and Mrs. Williams biological son.

7 Elaborate: You Are Hired* Background information: December 23, 1972, was the first day of work for a young nurse. It was an unusually busy night at the hospital and four beautiful babies were born. Five years later, Mr. and Mrs. Williams were involved in a car accident. Their son, John, was injured but later made a full recovery. The night of the accident, Mr. and Mrs. Williams found out that John was not their biological son. You have been hired by the Williams to locate their biological son. Through research, you learn that hair texture is controlled by incomplete dominance. Individuals who are homozygous dominant for hair texture have curly hair (CC). Individuals who are homozygous recessive have straight hair (cc). Individuals who are heterozygous have wavy hair (Cc). After reviewing your notes, you decide to concentrate on two key pieces of information: Mr. Williams is heterozygous for Type B blood and has wavy hair. Mrs. Williams is homozygous for Type A blood and has straight hair. The hospital records contain important information about the other children who were born in the hospital that day: Baby 1 is heterozygous for Type B blood and has wavy hair. Baby 2 has Type AB blood and has straight hair. Baby 3 is heterozygous for Type A blood and has curly hair. Your instructions: Work with your team to determine which baby is Mr. and Mrs. Williams biological son. STAAR Achievement Series for Science 2013 Region 4 Education Service Center

8 Name: Date: Evaluate: Predicting Genetic Outcomes 1 Sickle-cell anemia is a disease that occurs when an individual inherits two recessive alleles for sickle cell. Individuals with this disorder have a mutation in the hemoglobin protein that causes the blood cells to sickle (flatten with an irregular shape). Two individuals that are heterozygous for this allele marry and want to have children. Which of the following is true? A All of the children will have sickle-cell anemia. B There is a 25% chance their children will have sickle-cell anemia. C There is a 50% chance their children will have sickle-cell anemia. D There is a 3/16 chance their children will have sickle-cell anemia. R R r r Rr Rr Rr Rr 2 In the Punnett square above, R = red, r = white, and Rr = pink. The type of inheritance is F multiple allele inheritance G incomplete dominance H sex-linked inheritance J codominance STAAR Achievement Series for Science 2013 Region 4 Education Service Center

9 3 A species of chickens has feathers that are black and white in color. In chickens, black feathers and white feathers are codominant. What percentage of black and white feathered offspring would most likely result from a cross between two black-and-white-colored chickens? A 100% B 75% C 50% D 25% 4 Two parents plan to have children. The father is heterozygous for Type B blood. The mother is heterozygous for Type A blood. What are all the different genotypes that their children may inherit? F AB, AO, BO, or OO G Type A or Type B H OO, AA, or BB J Type A, Type B, Type AB, or Type O

10 5. In pea plants, round seed shape is dominant to wrinkled seed shape. Yellow seed color is dominant to green seed color. A wrinkled seed-shaped green plant is crossed with a pea plant that is heterozygous round seed shape and heterozygous yellow seed color. What are the genotypes and phenotypes of the resulting offspring? STAAR Achievement Series for Science 2013 Region 4 Education Service Center