In some cases of self-incompatibility, pollen tube growth is so slow that the st
ID: 150523 • Letter: I
Question
In some cases of self-incompatibility, pollen tube growth is so slow that the style withers and dies before fertilization can occur. Sometimes, if pollination is artificially accomplished in the bud stage, the llen tube can reach the ovary before the style withers. In this case, it is possible to produce a genot po homozygous at the self sterility locus A. What would be expected results from natural pollination of such a homozygote (S's) by a heterozygote containing one allele in common (S'S). Assume gametophytic self incompatibility for question 3 B. What would be the result of the reciprocal cross of part A? C. What would be the expected results of natural pollination of S's by S's'? D. Would the reciprocal cross of part C above make any difference in the expected progeny? 2. The self-incompatibility mechanism of many plants probably involves a series of multiple alleles similar to that found in Nicotiana (tobacco plant). In this species, pollen tubes grow very slowly, or not at all down the style that contains the same allele at the self-incompatibility locus S. Self incompatibility appears to involve an S-RNase enzyme. ren Pollen parent A. S'S B. S'S C. S's2 s's s'S S3S4 A. List the genotypic ratio of progeny sporophytes expected from the above crosses assuming gametophytic self-incompatiblilty B. List the genotypic ratio of progeny sporophytes expected from the above crosses assuming sporophytic self-incompatibility 3. A cross is made between two plants of the self-sterile genotype S's2x s'st. If all the Fi progeny are pollinated only by plants of genotype S'S, what genotypic proportions are expected in the F generation (assume gametophytic self-incompatibility). Answer to this question will be posted on Canvas 4. Why are plants such as wild tomato plants that undergo gametophytic self-incompatibility always 5. Would you expect the offspring of plants that use the sporophytic self-incompatibility system to 6. The hemp plant (Cannabis sativa) is normally a dioecious species. Occasionally, a male plant develops heterozygous for their S-alleles (S-haplotypes)? produce only heterozygotes for S-alleles? Why or why not? flowers which produce emale as well as male gametes (hermaphroditic plant). When such plants are self-fertilized (are self-compatible), they produce males and females in a 3:1 ratio. Explain genetically how this ratio occurs, and the genotypes of all males and female hemp plants. Kuspira & Walker 7. In sporophytic incompatibility, a component of the pollen coat contains factors that determine the specificity of self-incompatibility. The pollen coat contains molecules that were produced by the diploid tapetum. Predict what would happen if a compatible pollen grain was placed on the exact spot on the stigma that an incompatible pollen grain was placed and removed. (Buchanan). 8. Describe the signaling cascade that causes self-incompatibility in Brassica plants.Explanation / Answer
1. (A) Whwn a cross between the plants of the genotype S1S1 is carried out with the plant with genotype S1S3, then the filial 1 generation with genotype S1S1 and S1S3 would be obtained in a ratio of fifty percent.
(B) Two types of reciprocal cross would be carried out for the given genotype: 1. When a cross is made between the S1S1 and S1S3, the same fifty percent ratio of both progenies would be obtained. 2. When the second type of reciprocal cross is made between the S1S3 and S1S3, then the expected genotype of the plant would be 2 of S1S3, one of S1S1 and one of S3S3.
(C) The expected result which would be obtained by the cross of S1S1 and S2S3 is 50 percent ratio of both type of the genotype.
(D) The reciprocal cross would make differnece in the second type of reciprocal cross whcih woud be carried out between S2S3.
2. (A) The genotypic ratio for the cross between the S1S2 and S1S2 woud be S1S1: S1S2: S2S1: S2S2. The fifty percent ratio would be obtained from the cross between the S1S2 and S1S3. The expected result which would be obtained from the cross between the S1S2 and S3S4 would be S1S3 : S1S4: S2S3 : S2S4.
(B) The progenies having the genotype S1S1 and S2S2 would show the self incompatibility.
3, The differnt type of progenies would be obtained.
4. Because the S-Rnase gene determines the specificity of the S-allele.
5. The offsprings which would be heterozygous for the S-allele would not show the self incompatibility mechanisms.
6. The occurence of the ratio in the hemp plant can be due to the mechanisms of the incomplete dominance.
7. There would be the possibility of the pollination to occur if the compatible pollen is placed at the place of incompatible pollen at the stigma.
8. teh signalling cascade involves the events which are responisble for developing the entire mechanisms of the self incompatibility procedures in the Brassica.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.