Introduction to Genetic Analysis
11th Edition
ISBN: 9781464109485
Author: Anthony J.F. Griffiths, Susan R. Wessler, Sean B. Carroll, John Doebley
Publisher: W. H. Freeman
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Chapter 2, Problem 6P
Summary Introduction
To explain: The
Introduction: The first law of Mendel is known as the law of dominance. This law explains that each gene has two alleles that code for a specific trait. One of the alleles is always dominant, which means that it will always show, while the other allele is recessive meaning its presence can be masked by the dominant allele.
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A woman with fair skin, blond hair, and blue eyes gives birth to fraternal twins; the father has dark brown skin, dark hair, and brown eyes. One twin has blond hair, brown eyes, and light skin, and the other has dark hair, brown eyes, and dark skin. What Mendelian law does this real-life case illustrate and explain what this means in terms of the inherited alleles for these genes?
Mendel crossed pea plants that produced round seeds with those that produced wrinkled seeds. From a total of 7324 F2 seeds, 5474 were round and 1850 were wrinkled. Using the symbols W and w for genes, (a) symbolize the original P cross; (b) the gametes; and (c) F1 progeny, (d) Represent cross between two F1 plants (or one selfed); (e) symbolize the gametes; and (f) summarize the expected F2 results under the headings: phenotypes, genotypes, genotypic frequency, and phenotypic ratio.
Mendel's concept of dominance states that in a genotype where two different alleles of a locus are present, only the trait encoded by the dominant allele is observed. Give a molecular explanation for dominance, i.e. explain intracellular molecular events that can result in what we observe as dominance on a phenotypic level. Use the gene that encodes seed shape in peas as an example, where roun(R) is dominant over wrinkled(r), to explain how RR and Rr plants can have the same phenotype.
Chapter 2 Solutions
Introduction to Genetic Analysis
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- Gray seed color in peas is dominant to white. Assume that Mendel conducted a series of experiments where plants with gray seeds were crossed with each other and the following progeny were produced: 320 gray and 80 white. (a) What is the most probable genotype of each parent? (b) Based on your answer in (a) above, what genotypic and phenotypic ratios are expected in the progeny?arrow_forwardQ6. Guinea pigs, which were homozygous for long, black hair were crossed with ones which were homozygous for short, white hair. All the F1 offspring had short, black hair. (a) Using suitable symbols, draw a genetic diagram showing parents genotypes, to explain this result in F1 offspring. (b) Complete the Punnett square to show the results of interbreeding the F1 offspring. Gametesarrow_forwardIn Figure 2-11, assume (as in corn plants) that allele Aencodes an allele that produces starch in pollen and allele a does not. Iodine solution stains starch black. Howwould you demonstrate Mendel’s first law directly withsuch a system?arrow_forward
- In Mendel’s 1866 publication as shown in Figure 1-4, he reports 705 purple-flowered (violet) offspring and 224 white-flowered offspring. The ratio he obtained is 3.15:1 for purple: white. How do you think he explained the fact that the ratio is not exactly 3:1?arrow_forwardMendel describes subjecting each of the 34 varieties of peas he obtained to a two-year trial. During this time he let the plants self-fertilize and observed their offspring. What was he looking for, and what was the purpose of doing this two-year trial? Explain what Mendel means when he writes that the 3:1 ratio observed in the first generation from the hybrids "resolves itself" into a ratio of 2:1:1arrow_forwardOn the basis of Mendel’s observations (i.e. Mendelian patterns), predict the results from the following crosses with peas. Show the results in terms of genotypes, phenotypes, and their proportions in the offspring. The progeny of a tall (dominant and homozygous) variety crossed with a dwarf variety. The progeny of (a) self-fertilized. The progeny from (a) crossed with the original tall parent. The progeny of (a) crossed with the original dwarf parent.arrow_forward
- Mendelian ratios are modified in crosses involving autotetraploids.Assume that one plant expresses the dominant trait greenseeds and is homozygous (WWWW). This plant is crossed to onewith white seeds that is also homozygous (wwww). If only onedominant allele is sufficient to produce green seeds, predict theF1 and F2 results of such a cross. Assume that synapsis betweenchromosome pairs is random during meiosis.arrow_forwardMendel crossed true-breeding plants with wrinkled and green peas to true breeding plants with round and yellow peas. Then he crossed the Fl plants to true-breeding plants with wrinkled, green peas and observed in the progeny 31 plants with round, yellow peas, 26 plants with round, green peas, 27 plants with wrinkled, yellow peas, and 26 with wrinkled, green peas. a) What proportion of these four phenotypes would be expected? b) Calculate the appropriate chi-square and determine if it is consistent with Mendelian expectations (be sure to indicate the probability range).arrow_forwardThis question deals with Mendelian Genetics. Read each part carefully before you answer it. In the following questions, assume green pea pods are dominant over yellow pea pods. a) If a pea plant that is Heterozygous for pod color is crossed with a pea plant with yellow pods, what do you expect to see in the offspring (the f1 generation)? Specifically, what genotypes, what phenotypes, and in what ratios? (Use G for the green pod gene and g for the yellow pod gene.) (It is usually helpful to write out all the possible genotypes and give the phenotype for each genotype before answering the specific question.)arrow_forward
- Mendel found that round (R) seed is dominant over wrinkled (r) seed, and yellow (G) seed is dominant over green (g) seed. The following crosses were made between plants of known phenotypes but unknown genotypes: 1) round, yellow X round, yellow 2) round, yellow X round, yellow 3) round, yellow X wrinkled, green b) Cross 1 2 Using the same symbols as defined above, list the genotypes of the parent plants in each cross. 3 round, yellow X round, yellow round, yellow X round, yellow round, yellow X wrinkled, green Which of the above crosses is a testcross? Offspring and ratio 3/4 round, yellow 1/4 wrinkled, yellow 9/16 round, yellow 3/16 round green 3/16 wrinkled, yellow 1/16 wrinkled, green MacBook Pro 1/4 round, yellow 1/4 round, green 1/4 wrinkled, yellow 1/4 wrinkled, green Focuarrow_forwardThe allele G for yellow stigma is completely dominant to green (g). Supposing two strains of autotetraploid plants are available and their genotypes are as follows: GGgg – in this plant the gene is close to the centromere Gggg – in this plant the gene is far from the centromere If these two plants are crossed: a) provide the gametes that can be obtained from the two plants; b) provide the genotypic and phenotypic ratios of the offspring.arrow_forwardMendel describes subjecting each of the 34 varieties of peas he obtained to a two-year trial. During this time he let the plants self-fertilize and observed their offspring. What was he looking for, and what was the purpose of doing this two-year trial? Why did Mendel perform "reciprocal crosses"? Someone gives you a bag of yellow peas and you plant them in the Spring. Can you predict the color of the peas that will appear in the pods on the plants grown from these peas? Would your answer be different if you had received a bag of green peas? Explain what Mendel means when he writes that the 3:1 ratio observed in the first generation from the hybrids "resolves itself" into a ratio of 2:1:1arrow_forward
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