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18:27In pea plants, plant height, seed shape, and seed color are governed by three independently assorting genes. The three genes have dominant and recessive alleles, with tall (T) dominant to short (t), round (R) dominant to wrinkled (r), and yellow (G) dominant to green (g).
What proportion of the that produce round, green seeds (regardless of the height of the plant) are expected to breed true?
A variety of pea plant called Blue Persian produces a tall plant with blue seeds. A second variety of pea plant called Spanish Dwarf produces a short plant with white seed. The two varieties are crossed, and the resulting seeds are collected. All of the seeds are white; and when planted, they produce all tall plants. These tall F₁ plants are allowed to self-fertilize. The results for seed color and plant stature in the F₂ generation are as follows:
Which phenotypes are dominant, and which are recessive? Why?
A variety of pea plant called Blue Persian produces a tall plant with blue seeds. A second variety of pea plant called Spanish Dwarf produces a short plant with white seed. The two varieties are crossed, and the resulting seeds are collected. All of the seeds are white; and when planted, they produce all tall plants. These tall F₁ plants are allowed to self-fertilize. The results for seed color and plant stature in the F₂ generation are as follows:
F₂ Plant Phenotype Number
Blue seed, tall plant. 97
White seed, tall plant 270
Blue seed, short plant 33
White seed, short plant 100
TOTAL 500
What is the expected distribution of phenotypes in the F₂ generation?
A variety of pea plant called Blue Persian produces a tall plant with blue seeds. A second variety of pea plant called Spanish Dwarf produces a short plant with white seed. The two varieties are crossed, and the resulting seeds are collected. All of the seeds are white; and when planted, they produce all tall plants. These tall F₁ plants are allowed to self-fertilize. The results for seed color and plant stature in the F₂ generation are as follows:
F₂ Plant Phenotype Number
Blue seed, tall plant. 97
White seed, tall plant 270
Blue seed, short plant 33
White seed, short plant 100
TOTAL 500
Examine the data in the table by the chi-square test and determine whether they conform to expectations of the hypothesis.
In tomato plants, the production of red fruit color is under the control of an allele R. Yellow tomatoes are rr. The dominant phenotype for fruit shape is under the control of an allele T, which produces two lobes. Multilobed fruit, the recessive phenotype, has the genotype tt. Two different crosses are made between parental plants of unknown genotype and phenotype. Use the progeny phenotype ratios to determine the genotypes and phenotypes of each parent.
Cross 1 progeny:
3/8 two-lobed, Red
3/8 two-lobed, yellow
1/8 multilobed, Red
1/8 multilobed, Yellow
Cross 2 progeny:
1/4 two-lobed, Red
1/4 two-lobed, yellow
1/4 multilobed, Red
1/4 multilobed, yellow
During your work as a laboratory assistant in the research facilities of Dr. O. Sophila, a world-famous geneticist, you come across an unusual bottle of fruit flies. All the flies in the bottle appear normal when they are in an incubator set at 22°C. When they are moved to a 30°C incubator, however, a few of the flies slowly become paralyzed; and after about 20 to 30 minutes, they are unable to move. Returning the flies to 22°C restores their ability to move after about 30 to 45 minutes.
With Dr. Sophila's encouragement, you set up 10 individual crosses between single male and female flies that exhibit the unusual behavior. Among 812 progeny, 598 exhibit the unusual behavior and 214 do not. When you leave one of the test bottles in the 30°C incubator too long, you discover that more than 2 hours at high temperature kills the paralyzed flies. When you tell this to Dr. Sophila, he says, 'Aha! I know how to explain this condition.' What is his explanation?
