Concept explainers
a.
To determine: The conclusion for such a research results would lead to.
Introduction: Cytoplasmic male sterility is total or partial male sterility in plants as the result of specific nuclear and mitochondrial interactions.
b.
To determine: The genotype and the
Introduction: Male sterility is the failure of plants to produce functional anthers, pollen, or male gametes.
c.
To determine: The results of the testcross and genotypes and phenotypes.
Introduction: In corn breeding, the cytoplasm that was used initially to provide the male sterility was the Texas or T cytoplasm.
d.
To determine: The result of a cross in which the male parent is
- (i) heterozygous at both restorer loci.
- (ii) homozygous dominant at one restorer locus and homozygous recessive at the other.
- (iii) heterozygous at one restorer locus and homozygous recessive at the other.
- (iv) heterozygous at one restorer locus and homozygous dominant at the other.
Introduction: Hybrid production requires a plant from which no viable male gametes are introduced, and this selective exclusion of viable male gametes can be accomplished via different paths.
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Introduction to Genetic Analysis
- In corn, male sterility is controlled by maternal cytoplasmic elements. This phenotype renders the male part of corn plants (i.e. the tassel) unable to produce fertile pollen; the female parts, however, remain receptive to pollination by pollen from male-fertile corn plants. However, the presence of a nuclear fertility restorer gene F restores fertility to male-sterile lines. Using the following color-coded circles, simulate the crosses indicated below. Put the illustrations of crosses in the spaces provided. Be sure to include in the labels the genotypes and phenotypes of the offspring in each cross. Big light green circle - male-sterile cytoplasm Big orange circle - male-fertile cytoplasm Small orange circle - FF nucleus Small half-light green-half-orange circle - Ff nucleus Small light-green circle - ff nucleusarrow_forwardIn com, male sterility is controlled by maternal cytoplasmic elements. However, the presence of a nuclear fertility restorer gene (F_) restores fertility to male sterile lines. a. What are the crosses male sterile female x FF male? Give the genotypes and phenotypes of the offspring in each cross. Explain.arrow_forwardConsider a maize plant: Genotype C/cm ; Ac/Ac+ where cm is an unstable colorless allele caused by Ds insertion. What phenotypic ratios would be produced and in what proportions when this plant is crossed with a mutant c/c Ac+/Ac+? Assume that the Ac and c loci are unlinked, that the chromosome-breakage frequency is negligible, and the C allele encodes pigment production.arrow_forward
- Chlamydomonas, a eukaryotic green alga, may be sensitive to the antibiotic erythromycin, which inhibits protein synthesis in bacteria. There are two mating types in this alga, mt+ and mt-. If an mt+ cell sensitive to the antibiotic is crossed with an mt- cell that is resistant, all progeny cells are sensitive. The reciprocal cross (mt+ resistant and mt- sensitive) yields all resistant progeny cells. Assuming that the mutation for resistance is in the chloroplast DNA, what can you conclude from the results of these crosses?arrow_forwardWild-type strains of the haploid fungus Neurospora canmake their own tryptophan. An abnormal allele td renders the fungus incapable of making its own tryptophan.An individual of genotype td grows only when its medium supplies tryptophan. The allele su assorts independently of td; its only known effect is to suppress the tdphenotype. Therefore, strains carrying both td and su donot require tryptophan for growth.a. If a td ; su strain is crossed with a genotypically wildtype strain, what genotypes are expected in the progenyand in what proportions?b. What will be the ratio of tryptophan-dependent totryptophan-independent progeny in the cross of part a?arrow_forwardA yeast geneticist irradiates haploid cells of a strain that is an adenine-requiring auxotrophic mutant, caused by mutation of the gene ade1. Millions of the irradiated cells are plated on minimal medium, and a small number of cells divide and produce prototrophic colonies. These colonies are crossed individually with a wildtype strain. Two types of results are obtained:(1) prototroph × wild type : progeny all prototrophic(2) prototroph × wild type : progeny 75% prototrophic, 25% adenine-requiring auxotrophsa. Explain the difference between these two types of results.b. Write the genotypes of the prototrophs in each case.c. What progeny phenotypes and ratios do you predict from crossing a prototroph of type 2 by the original ade1auxotroph?arrow_forward
- In a wild-type fungus, protein E (encoded by the haplosufficient gene E) normally dimerizes to catalyzes a biochemical reaction necessary for the production of a dark pigment. Ed represents a mutant, dominant negative allele of gene E. What is the predicted phenotype of a fungus cell of genotype E*/Ed, and why? O wild type (normal production of the dark pigment), as E is haplosufficient mutant (no pigment production), as no dimers will form in the heterozygous mutant (no pigment production), as the mutant allele Eg is dominant O wild type (normal production of the dark pigment), as dimers of wild-type and mutant protein E will be formed in the heterozygousarrow_forwardMultiple crosses were made between true-breeding lines of black and yellow Labrador retrievers. All the F1 progeny were yellow. When these progeny were intercrossed, they produced an F2 consisting of 121 yellow, 9 black and 30 chocolate. What epistatic ratio and what kind of epistasis is approximated in the F2? Propose a biochemical pathway for coat color in Labrador retrievers based on the type of epistasis. Correlate each genotype with the phenotype that would occur in your pathway. Also show the frequency of each genotype. A-B- A-bb aaB- aabbarrow_forwardA form of male sterility in corn is inherited maternally. Marcus Rhoades first described this cytoplasmic male sterility by crossing female gametes froma male sterile plant with pollen from a male fertileplant. The resulting progeny plants were malesterile.a. Diagram the cross, using different colors andshapes to distinguish between nuclear (lines) andcytoplasmic (circles) genomes from the male sterile (one color) and male fertile (another color)strains.b. Female gametes from the male sterile progenywere backcrossed with pollen from the same malefertile parent of the first cross. The process was repeated many times. Diagram the next two generations including possible crossover events.c. What was the purpose of the series of backcrosses?[Hint: Look at your answer to part (b) and thinkabout what is happening to the nuclear genome.]Why could Rhoades interpret these results as ademonstration of cytoplasmic male sterility?arrow_forward
- In humans, dosage compensation is accomplished by: inactivating one X chromosome in female somatic cells inactivating one homolog from each homologous pair of chromosomes in female somatic cells inactivating the Y chromosome in male somatic cells increasing gene expression from the X chromosome in male somatic cellarrow_forwardSome sweet-pea plants have purple flowers and others have white flowers. A homozygous variety of sweet pea that has purple flowers is crossed with a homozygous variety that has white flowers. All the F1have purple flowers. When these F1 self-fertilize, the F2 appear in a ratio of 916 purple to 716 white. a.Draw a hypothetical biochemical pathway to explain the production of purple and white flowers in sweet peas.arrow_forwardDrosophila (fruit-flies) mutants A and B have the same phenotype: the absence of red pigment in the eyes. Homozygous mutants were crossed, and all offspring possessed red eyes. Does the appearance of red eyes in the progeny indicate complementation or a failure to complement? [Select] Do the mutants likely have mutations in the same or different genes? [ Select]arrow_forward
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