Concept explainers
Two genes, designated A and B, are located
A.
B.
C.
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Genetics: Analysis and Principles
- Nicotiana glutinosa (2 n = 24) and N. tabacum (2 n = 48) are two closely related plants that can be intercrossed, but the F1 hybrid plants that result are usually sterile. In 1925, Roy Clausen and Thomas Goodspeed crossed N. glutinosa and N. tabacum and obtained one fertile F1 plant . They were able to self-pollinate the flowers of this plant to produce an F2 generation. Surprisingly, the F2 plants were fully fertile and produced viable seeds. When Clausen and Goodspeed examined the chromosomes of the F2 plants, they observed 36 pairs of chromosomes in metaphase I and 36 individual chromosomes in metaphase II. Explain the origin of the F2 plants obtained by Clausen and Goodspeed and the numbers of chromosomes observed.arrow_forwardTwo pure-breeding parents produced a heterozygous female offspring (AaBb) that was then testcrossed with an aabb male. The offspring produced from the testcross included 50 AaBb, 450 Aabb, 450 aaBb, 50 aabb individuals. Describe how you can tell if these two genes are linked or unlinked (What ratio would you expect to see from the testcross if they were not linked?). What were the genotypes of the original parents that produced the heterozygous female? What is the genetic map distance between the two genes?arrow_forwardAssume that the trihybrid cross AABBrr x aabbRR is made in a plant species. Assume that A and B are dominant alleles, but there is no dominance effect of alleles at the R locus. a) How many different gametes are possible in the F1generation? What are the genotypes of these gametes? b) What is the probability of the parental aabbRR genotype in the F2 progeny? c) What proportion of the F2 progeny would be expected to be homozygous for all three genes?arrow_forward
- In the snail Limnaea peregra, coiling of the shell is determined by the genes D for right-hand coiled shells, and d for left-hand coiled shells. The gene for the right-hand coiled shell is dominant. The direction of coiling is determined by the genotype of the maternal parent producing the egg, regardless of the progeny's genotype. Which of the following crosses could give a left-hand coiled shell heterozygote? A. right-hand coiled dd female X left-hand coiled DD male B. left-hand coiled DD female X right-hand coiled dd male C. left-hand coiled DD female X left-hand coiled DD male D. right-hand coiled dd female X left-hand coiled dd malearrow_forwardIn barley, a self-fertilizing species that can be cross-fertilized, two true-breeding strains with virescent leaves occur. In strain A, the trait is caused by a cytoplasmic gene while in strain B it is by a recessive chromosomal gene. What phenotypes would you expect among the progeny, and in what proportions in each of the following? Illustrate your crosses below, indicate and the female and male parent for each cross, and write the phenotype of all the parents and offspring(s). a. reciprocal crosses between A and Barrow_forwardA pure breeding strain of squash that produced disk-shaped fruits was crossed with a pure- breeding strain having long fruits. The first filial generation had disk fruits, but the second filial generation showed a new phenotype, sphere, and was composed of the following proportions: disk 270, sphere 178, long 32. Propose an explanation for these results, and show the genotypes of P, First filial generation and second filial generation.arrow_forward
- In barley, a self-fertilizing species that can be cross-fertilized, two true-breeding strains with virescent leaves occur. In strain A, the trait is caused by a cytoplasmic gene while in strain B it is by a recessive chromosomal gene. What phenotypes would you expect among the progeny, and in what proportions in each of the following? Illustrate your crosses below, indicate and the female and male parent for each cross, and write the phenotype of all the parents and offspring(s). a. reciprocal crosses between A and Bb. crossing of each F1 in (a) to each of the paternal strainsc. self-fertilization of the F1’s in (a)d. reciprocal crosses between F1’s in (a) Use the following gene assignments: Strain A (trait is in Cytoplasm) A – virescent a – not virescent Strain B (recessive chromosomal gene) B – not virescent b - virescentarrow_forwardYou have a pure breeding plant with red flowers, yellow seeds and red-veined leaves. You cross this with another pure breeding plant that has white flowers, pink seeds and yellow leaf veins. All of the offspring (F1) have white flowers, yellow seeds and orange leaf veins. Assuming all three loci are independently assorting, use this information to answer the following question: If two F1 offspring are crossed with each other and 1000 F2 are obtained, approximately how many offspring should have orange leaf veins? a. 1000 b. 750 c. 500 d. 250 e. Cannot be determined with this informationarrow_forwardIn a species of firefly, wide wings (W) are dominant to narrow wings (w) and graybodies (C) are dominant to brown bodies (c). A WwCc and wwcc fly were mated andproduced the following offspring: (in the picture attached) What is the recombination frequency for this cross (in percent)?arrow_forward
- In a variety of tomato plant ,the leaves maybe pure green,pure white,or variegated (mixture). a)when 2 variegated plants were crossed,87 offspring were produced,of these 20 were green,46 were variegated and 21 remain died soon after germination.Draw a genetic diagram to explain these results,why did 21 of them diedarrow_forwardThe cross between + + +/ a b c and a b c / a b c in fruitflies yields the following crossover results: a – b single crossovers: 5.75% b – c single crossovers: 8.08% a – c single crossovers: 0.25 % Calculate the coefficient of coincidence, accurate to three decimal places.arrow_forwardIn a cross between a white-eyed female (ww) and a red-eyed male (w+Y), nearly all the progeny were either red-eyed females (w+w) or white-eyed males (wY). However, about 1 in every 2000 F1 flies had an "exceptional phenotype" and was either a white-eyed female or red-eyed male. How did Bridges explain this unexpected result? A) Crossing over B) Incomplete cytokinesis C) Incorrect synapsis D) Nondisjunction E) Pseudoautosomal regionarrow_forward
- Biology (MindTap Course List)BiologyISBN:9781337392938Author:Eldra Solomon, Charles Martin, Diana W. Martin, Linda R. BergPublisher:Cengage Learning