Bio Mastering Chapter 14

12/8/2020 Chapter 14 Chapter 14 Due: 11:59pm on Monday, December 14, 2020 Mendel's Law of Segregation This tutorial introduces Mendel’s law of segregation of alleles using monohybrid crosses, the addition and multiplication rules, conditional probability, and binomial probability. In this tutorial you will investigate how alleles segregate during meiosis. You will also explore how this segregation, in conjunction with random gamete fusion, allows geneticists to predict the outcome of genetic crosses using simple rules of probability. Part A - Allele segregation and gamete formation One character in peas that Mendel studied was yellow versus green seeds. A cross between a homozygous yellow line (YY) and a homozygous green line (yy) will result in F1 plants that are heterozygous (Yy) for this trait and produce yellow seeds. When an F1 plant undergoes meiosis, what gamete types will it produce, and in what proportions? Hint 1. How do alleles segregate during gamete formation? According to Mendel’s law of segregation, a gamete ANSWER: always receives both of the parent’s alleles for each gene. always receives only one of the parent’s alleles for each gene. may receive either one or two of the parent’s alleles for each gene. Hint 2. Does allele segregation determine gamete frequencies (i.e., proportions)? According to Mendel’s law of segregation, ANSWER: dominant alleles segregate into gametes more frequently than recessive alleles. allele frequencies (i.e., proportions) in gametes cannot be predicted in advance. alleles segregate into gametes with equal frequency. ANSWER: 1/45 12/8/2020 Chapter 14 Yy Yy Y y Y y YY Y yy y Correct Mendel’s law of segregation states that allele pairs segregate equally into gametes during meiosis. This means that a gamete will have only one allele of any given gene, and that the probability of a gamete having one allele or the other is equal (and therefore ½, or 50%, for either allele). Part B - Punnett square Punnett squares are convenient ways to represent the types and frequencies of gametes and progeny in experimental crosses. This Punnett square shows the results of a Yy x Yy cross to form F2 progeny. Use your understanding of Mendel’s law of segregation and the rules of probability to complete the Punnett square for this cross. First identify the gametes. Use pink labels to identify the male and female gamete types and white labels to identify the gamete frequencies. Then identify the F2 progeny. Use pink labels to identify the progeny genotypes and white labels to identify the progeny frequencies. Hint 1. Setting up a Punnett square To create a Punnett square, list the possible gametes from one parent down one side and the possible gametes from the other parent across the top. Each gamete is assigned a frequency according to Mendel’s law of segregation (as explained in Part A). The boxes inside the Punnett square represent the genotypes of the progeny that result from random gamete fusion. Progeny frequencies are then calculated using the frequencies of the gametes that formed them. (See Hint 2.) Hint 2. How do I calculate the frequencies of the F2 progeny? Which statement correctly explains how to determine the frequencies of the F2 progeny? ANSWER: The progeny frequencies are determined by the addition rule (adding the gamete frequencies together). The progeny frequencies are determined by the multiplication rule (multiplying the gamete frequencies together). The progeny frequencies cannot be predicted from gamete frequencies. ANSWER: 2/45 12/8/2020 Chapter 14 Reset Y y YY Yy Help yy Y Yy Y y y Yy Correct A Punnett square is a convenient method for representing Mendel’s law of segregation in a visual form. Using a Punnett square allows one to easily see gamete types and frequencies, as well as the genotypes and frequencies of progeny formed by random gamete fusion. The genotype frequencies inside a Punnett square are calculated using the multiplication rule: The probability of two independent events occurring simultaneously is the product of their individual probabilities. In this example, the genotype frequencies inside the square (¼) are the product of the gamete frequencies that led to their formation (½ x ½ = ¼). Part C - Using the Punnett square to make predictions Use the completed Punnett square in Part B to answer the questions below about the F2 generation. Drag the probabilities on the left to the blanks on the right to answer the questions. Terms can be used once, more than once, or not at all. Hint 1. How to choose between the addition rule and the multiplication rule The addition (or sum) rule is used when there is more than one way to fulfill the requirements of the event of interest. Often the word “or” acts as a hint that the addition rule is needed. For example, you might say, “Yy individuals in the F2 can be formed by either a Y from the female parent and a y from the male parent OR a y from the female parent and a Y from the male parent." This indicates that there are two ways to fulfill the requirement of “an F2 progeny with genotype Yy” in this case, and tells you that the addition rule should be used. The multiplication (or product) rule is used to determine the probability of simultaneous events with individual probabilities. Often the word “and” acts as a hint for the multiplication rule. For example, you might say “YY individuals in the F2 require a Y from the female parent AND a Y from the male parent." In this case, there is only one way to achieve the desired event. Therefore, the addition rule is not needed, and the probability of the YY genotype in the F2 is determined with the multiplication rule alone. Hint 2. For question 2, how do you account for conditional probabilities? Conditional probabilities apply when the pool of possible outcomes is reduced in some way by additional criteria. For example, determining probabilities for genotypes within only the yellow seeds in the F2 restricts the total number of possibilities because it excludes green seeds by definition. Use your knowledge of conditional probabilities and the Punnett square in Part B to answer this question. What is the probability that an F2 seed chosen at random from among only the yellow seeds will have a genotype of Yy? ANSWER: 3/45 12/8/2020 Chapter 14 3/4 2/3 1/2 Hint 3. How to approach questions 3 and 4 For questions 3 and 4, you need to consider all possible groupings and orders of three F2 seeds and their probabilities (determined using the multiplication rule). The table below shows all the possible groupings of three F2 seeds. Two of the probabilities have been filled in for you. Complete the table by calculating all of the other probabilities. Possible grouping Probability 1. Green, Green, Green ? 2. Yellow, Green, Green 3. Green, Yellow, Green ? 4. Green, Green, Yellow ? 5. Yellow, Yellow, Green ? 6. Yellow, Green, Yellow ? 7. Green, Yellow, Yellow ? 8. Yellow, Yellow, Yellow ? Once you’ve filled in the table, you will be able to calculate the probability of any defined outcome, employing the multiplication and addition rules as needed. (See Hint 1.) For example, to determine the probability of getting two green seeds and one yellow seed in a three-seed grouping, there are three groupings that qualify: Yellow, Green, Green Green, Yellow, Green Green, Green, Yellow After you've calculated the individual probabilities of these three groupings (using the multiplication rule) you can then employ the addition rule to calculate their combined probability (because any of these three outcomes meets the stated criterion of having one yellow seed and two green seeds). ANSWER: 4/45 12/8/2020 Chapter 14 Reset Help 1. What is the probability that an F2 seed chosen at random will be yellow? 2. What is the probablity that an F2 seed chosen at random from among the yellow seeds will breed true when selfed? 0 3. What is the probability that three F2 seeds chosen at random will include at least one yellow seed? 4. What is the probability that three F2 seeds chosen at random will include one green seed and two yellow seeds? 1 Correct Question 1 simply asks about the probability of forming a yellow seed in the F2, which is 3/4. Question 2 introduces the concept of conditional probability. Although there are two genotypes in the F2 that will breed true (YY and yy), only one of them is yellow. Thus, the question adds a new condition: Among yellow seeds only, 1/3 are true-breeding. Questions 3 and 4 require a full evaluation of all eight possible groupings of three randomly selected F2 seeds. Each grouping has its own probability, shown in the table below. For question 3, there are seven possible groupings that have at least one yellow seed (shown in blue in the table); the sum of their individual probabilities yields the final answer (63/64). Note that you could have also calculated this answer by subtracting the probability of the one category that doesn’t fit the criterion (Green, Green, Green) from the total probability (1 – 1/64 = 63/64). For question 4, there are three possible groupings that have one green and two yellow seeds (shown in bold in the table); the sum of their individual probabilities yields the final answer (27/64). Possible grouping Probability 1. Green, Green, Green 2. Yellow, Green, Green 3. Green, Yellow, Green 4. Green, Green, Yellow 5. Yellow, Yellow, Green 6. Yellow, Green, Yellow 7. Green, Yellow, Yellow 8. Yellow, Yellow, Yellow Determining Genotype: Pea Pod Color 5/45 12/8/2020 Chapter 14 A botanist has acquired a group of sweet pea plants. All of the plants have yellow pea pods (the recessive trait), except for one, which has green pea pods (the dominant trait). Pea pod color is a trait caused by a single gene. In this tutorial, you will determine how the botanist can identify the genotype of the green pea pod, and how this relates to Mendel’s laws and meiosis. Part A - Identifying the genotype How could the botanist best determine whether the genotype of the green-pod plant is homozygous or heterozygous? Hint 1. Definitions of genotype, homozygous, and heterozygous Genotype: the genetic makeup (allele composition) of one or more genes in an organism Homozygous: having two identical alleles for a given gene Heterozygous: having two different alleles for a given gene Hint 2. What possible genotypes could the green-pod plant have? Which of the following genotypes could the green-pod plant have? (G is the symbol for the green-pod allele; g is the symbol for the yellow-pod allele.) Select all that apply. ANSWER: gg Gg GG ANSWER: Self-pollinate the green-pod plant. Cross the green-pod plant with a yellow-pod plant. Cross the green-pod plant with another green-pod plant. Correct A cross between a plant of unknown genotype and one that is known to be homozygous recessive is called a test cross because the recessive homozygote tests whether there are any recessive alleles in the unknown. Because the recessive homozygote will contribute an allele for the recessive characteristic to each offspring, the second allele (from the unknown genotype) will determine the offspring’s phenotype. Part B - Diagramming a cross using a Punnett square Punnett squares can be used to predict the two possible outcomes of the botanist’s test cross. The Punnett square on the left shows the predicted result if the unknown plant is homozygous (GG); the Punnett square on the right shows the predicted result if the unknown plant is heterozygous (Gg). Drag the labels to the correct locations on the Punnett squares. (G is the symbol for the green-pod allele and g is the symbol for the yellow-pod allele.) You can use a label once, more than once, or not at all. Hint 1. How to create a Punnett square Follow these steps to create a Punnett square: 1. Determine the possible gametes that each parent could produce. (Remember that a gamete will have one allele for a given gene.) 2. For one parent, write the allele for each gamete along the top of the square. 3. For the other parent, write the allele for each gamete down the left side of the square. 4. Copy the alleles from the top into the boxes beneath them. Copy the alleles from the left into the boxes to their right. 5. Each of the boxes in the completed Punnett square represents the likelihood that one of the offspring will inherit that allele combination (or genotype). Hint 2. What does a Punnett Square predict? 6/45 12/8/2020 Chapter 14 Which statement correctly describes what a Punnett square predicts? ANSWER: Each box represents the probability that any one offspring from the cross would have a particular genotype. Each box represents one of the offspring that will definitely be produced from the cross. Each box represents the alleles that will be found in one of the offspring from the cross. ANSWER: Reset gg GG g G Gg g G Gg Gg Gg Gg Help g g Gg Gg gg gg Correct The genotypes in a Punnett square show all the possible combinations of alleles in offspring that could result from the particular cross. A Punnett square reveals the expected probabilities of each genotype among the offspring. For example, the Punnett square on the right reveals that there is a 50% chance that each offspring will have green pods and a 50% chance that each offspring will have yellow pods. This botanist used the same logic to reach her conclusions as Mendel used in his experiments. Part C - Relationship with Mendel’s findings Suppose that the botanist carried out the test cross described in Parts A and B and determined that the original green-pod plant was heterozygous (Gg). Which of Mendel’s findings does her test cross illustrate? Hint 1. Can you match the genetic principle to its description? Drag the terms on the left to the blanks on the right to match each description with the correct genetic principle. ANSWER: 7/45 12/8/2020 Chapter 14 Reset Help 1. Genes that are located on the same chromosome tend to be inherited together. linkage 2. During gamete formation, the two alleles for each gene separate so that each gamete receives only one allele. law of segregation 3. During gamete formation, the alleles for one gene separate independently of the alleles for all other unlinked genes. law of independent assortment 4. Genes are located on chromosomes; the behavior of chromosomes during meiosis accounts for inheritance patterns. chromosome theory of inheritance Hint 2. What Mendel did not know Mendel did not know that the “hereditary factors" he described were genes. He also did not know that genes are regions of chromosomes. It wasn’t until 1902, when Sutton and others proposed the chromosome theory of inheritance, that the relationship between Mendel’s “factors” and loci along chromosomes became known. ANSWER: chromosome theory of inheritance linkage law of independent assortment law of segregation Correct The law of segregation states that the two alleles for a gene separate during gamete formation, and end up in different gametes. In the case of the heterozygous green-pod plant (Gg), one gamete will receive the dominant allele (G), and the other gamete will receive the recessive allele (g). The law of segregation accounts for the prediction that 50% of the offspring of the test cross will have green pods and 50% will have yellow pods. Part D - Relationship of allele behavior to meiosis During which part of meiosis (meiosis I or meiosis II) do the two alleles of a gene separate? During which phase does the separation occur? State your answer as meiosis I or meiosis II followed by a comma and the name of the phase (for example, if your answer is meiosis II and metaphase, enter meiosis II, metaphase). Hint 1. What are the key events of the stages of meiosis? Drag the words on the left to the appropriate blanks to complete the sentences on the right. ANSWER: 8/45 12/8/2020 Chapter 14 Reset Help 1. During metaphase I , pairs of homologous chromosomes align in the center of the cell. 2. During telophase II , the separated chromatids elongate and (usually) cytokinesis occurs, forming four genetically distinct haploid daughter cells. 3. During anaphase I , homologous chromosomes separate by moving with the spindle microtubules toward the poles. 4. During prophase II , a spindle apparatus forms and individual chromosomes (each composed of sister chromatids) begin to move toward the center of the cell. 5. During prophase I , chiasmata form and crossing-over occurs. 6. During anaphase II , sister chromatids separate and move toward the poles. 7. During telophase I , the separated chromosomes cluster at the poles of the spindle and cytokinesis occurs, forming two daughter cells, each with a haploid set of replicated chromosomes. 8. During metaphase II , individual chromosomes (each composed of sister chromatids) align in the center of the cell. Hint 2. Differences between meiosis I and meiosis II In meiosis I, the major events are the pairing of homologous chromosomes during prophase and their separation during anaphase. In meiosis II, the major event is the separation of sister chromatids during anaphase. ANSWER: meiosis I, anaphase Correct Alleles separate from one another during anaphase of meiosis I, when the homologous pairs of chromosomes separate. Chapter 14 Question 16 Part A 9/45 12/8/2020 Chapter 14 Why did all of the F1 offspring of Mendel's classic pea cross always look like one of the two parental varieties? ANSWER: No genes interacted to produce the parental phenotype. The traits blended together during fertilization. One allele was dominant. Each allele affected phenotypic expression. Correct Chapter 14 Question 11 Part A Mendel's law of independent assortment has its basis in which of the following events of meiosis I? ANSWER: the division of cells at telophase alignment of pairs of homologous chromosomes along the middle of the cell synapsis of homologous chromosomes crossing over of homologous pairs of chromosomes Correct Chapter 14 Question 6 Part A Which of the following statements about independent assortment or segregation is correct? ANSWER: The law of segregation is accounted for by anaphase of mitosis. The law of segregation describes the behavior of two or more genes relative to one another. The law of independent assortment describes the behavior of two or more genes relative to one another. The law of independent assortment is accounted for by observations of prophase I of meiosis. Correct Chapter 14 Pre-Test Question 3 Part A What is an allele? See Concept 14.1 (Page 271) Hint 1. 10/45 12/8/2020 Chapter 14 How are genes related to alleles? What do loci have to do with it? ANSWER: the recessive form of a gene the dominant form of a gene an alternative version of a gene a variety of pea plant used by Mendel a type of chromosome Correct A diploid organism carries two alleles for each autosomal gene. The two alleles are found at comparable locations (loci) on homologous chromosomes. The alleles may be identical or slightly different, but they affect the same genetic character. Chapter 14 Question 1 Part A Which of the following statements is correct in describing the terms monohybrid cross and dihybrid cross? ANSWER: A monohybrid cross involves a single parent, whereas a dihybrid cross involves two parents. A monohybrid cross results in a 9:3:3:1 ratio, whereas a dihybrid cross gives a 3:1 ratio. A monohybrid cross is performed for one generation, whereas a dihybrid cross is performed for two generations. A dihybrid cross involves organisms that are heterozygous for two characters that are being studied, and a monohybrid cross involves organisms that are heterozygous for only one character being studied. Correct Activity: Monohybrid Cross Click here to complete this activity. Then answer the questions. Part A The result of the following cross indicates the orange eyes are _____ black eyes. 11/45 12/8/2020 Chapter 14 ANSWER: dominant to incompletely dominant to co-dominant to recessive to larger than Correct The result of this cross indicates that both parents are heterozygous for eye color. Part B If B represents the allele for black eyes (dominant) and b represents the allele for orange eyes (recessive), what would be the genotypic ratio of a cross between a heterozygous black-eyed MendAlien and an orange-eyed MendAlien? ANSWER: 0 homozygous black (BB): 0 heterozygote (black) (Bb): 1 homozygous orange (bb) 1 homozygous black (BB): 1 heterozygote (black) (Bb): 1 homozygous orange (bb) 1 homozygous black (BB): 0 heterozygote (black) (Bb): 1 homozygous orange (bb) 2 homozygous black (BB): 1 heterozygote (black) (Bb): 1 homozygous orange (bb) 0 homozygous black (BB): 1 heterozygote (black) (Bb): 1 homozygous orange (bb) Correct The heterozygous black-eyed MendAlien has the genotype Bb. The orange-eyed MendAlien has the genotype bb. The result of this cross is two Bb offspring and two bb offspring. This 2:2 ratio reduces to 1:1. Part C If B represents the allele for black eyes (dominant) and b represents the allele for orange eyes (recessive), what would be the phenotypic ratio of a cross between a heterozygous black-eyed MendAlien and an orange-eyed MendAlien? ANSWER: 1 black : 0 orange 3 black : 1 orange 1 black : 1 orange 0 black : 1 orange 1 black : 3 orange 12/45