W13 Prac questions Flashcards
The ripening seed consists of 3 genetically different systems. Name the systems and say why they are genetically different.
Seed shell (sameschale), Embryo, and Endosperm. Seed shell has 2n genome from the mother plant; the embryo has 2n genome which is a fusion of male and female products of meiosis. The endosperm has a 3n genome, 2 from the female and one from the male product of meiosis.
An Arabidopsis mutant has a mortality rate of 50% for all seeds. Why can you know that recessive embryonal factors cannot alone be responsible for this?
If embryonal factors for responsible, only max 25% of the seeds would die, and only those which were homozygous for the mutation. The observation of 50% shows that it must be gametophytic. The gametophyt is haploid, so there are only two forms, mutant or not.
Could maternal effects cause the death of 50% of the seeds? What maternal effects do you know, and how can you test them?
Sporophytic and gametophytic maternal effects.
Test: Cross a mutant female and a wild-type male and vice versa, if the results are not identical, then maternal effects are present.
If the factor is necessary for the development of the female gametophyte, the mutant can only be inherited through the male, and vice versa.
The pattern forming during the enbryogenesis is a process that starts at the first cell division. Why was a genetic screen for such mutants very successful even though the scientists didn’t look at the earliest embryo stages rather they screened the sprouts?
Mutant genes which normally control pattern forming but not essential cellular processes can lead to a halt in development. Such mutants be easy do screen due to the abnormal development of the sprouts.
In a genetic screen for embryo development mutants, mutants are found in which 75% of the seeds die. Microscopic analysis of the embryos shows that they develop into a ball shape, and don’t develop further. What statements can you make about the wild-type function of the mutants?
The wild-type function of the mutant gene is needed for the transition from a globular stage to a heart stage of the Embryo. Because 75% of the seeds die, it must be a dominant mutation.
The first cleavage of a fertilized cell, the zygote, happens in normal Arabidopsis development asymmetrically, after which the two daughter cells make fully defined and different development. What are the possible ways a cell can be “defined” and thus influence the cell cleavage? What would be the main characteristics of a model system for the study of this process?
Asymmetry is important through clustering of receptors, build-up of a cytoplasmic gradients.
Characteristics of a model system include: easy to access experimentally, best of all a see through egg cell.
