Honor System


Course Topics


Homework Assignment - Maternal Effects and Maternal Inheritance

100 points total (25 points each)

Use complete sentences in all of your answers where appropriate. If you are stumped by a problem, explain as much as you can to get partial credit.

1. From your experience as a geneticist, you are aware that variegation of leaf tissue can be controlled by nuclear or cytoplasmic genes. A student brings to you a variegated spider plant. This plant appears different than the spider plants that you have seen previously which were entirely green. Design an experiment to determine the mode of inheritance of the variegated phenotype. Include in your discussion, the results you might expect and what those results could imply regarding the mode of inheritance.

2. Chlamydomonas is a single-celled haploid algae that contains a single large chloroplast. Further, it is relatively easy to manipulate Chlamydomonas in culture. For meiosis to occur, two haploid cells fuse. Fusion only occurs between cells of the opposite mating types (mt+ and mt-). Streptomycin-resistance Chlamydomonas cell lines have been developed, and these cell lines can be screened in culture. The following are the results of two matings. From these results, propose a genetic explanation for the inheritance of streptomycin-resistance.

Note:Streptomycin resistant = str-r; Streptomycin sensitive = str-s

Cross Progeny
str-r, mt+ X str-s, mt- all progeny cells are str-r
str-s, mt+ X str-r, mt- all progeny cells are str-s

3. Male sterility/fertility in corn is controlled by nuclear and cytoplasmic factors.

a. If a male sterile female is pollinated by a plant heterozygous for Rf1, the original restorer gene, what are the genotypes and phenotypes of the progeny with respect to the cytoplasmic and nuclear genes?

b. In addition to the original restorer of fertility gene, Rf1, a second independently assorting restorer gene, Rf2 was found in corn. A male sterile female was crossed with plants with the following genotypes. What segregation patterns would you expect from each mating?

Mating Cross
1 Male sterile female x Rf1rf1Rf2rf2 male
2 Male sterile female x Rf1Rf1rf2rf2 male
3 Male sterile female x rf1rf1Rf2rf2 male
4 Male sterile female x Rf1rf1Rf2Rf2 male

4. Two lines of bean plants are being studied. One line is black-seeded, and the other is white-seeded. The two are crossed in a reciprocal manner. The F1 seed from one cross (black-seeded female) is black-seeded. The F1 seed from the second cross made with a white-seeded female is white-seeded. The F1 generation is selfed, and all F2 seeds express the ambigua phenotype (all black except for small splashes of white on one end of the seed). The F2 generation was selfed, and the F3 distributions were the same for each original reciprocal cross. The F3 distributions were:

1/4 Black
1/2 Ambigua
1/16 Virgarcus (black color extending over 1/2 of the seed; otherwise white)
1/8 Weak Virgarcus (black color extending over 1/8 of the seed; otherwise white)
1/16 White

Completely explain all of the results from this results of these crosses. (Hint: You will need to study this problem at the complete genotype level to determine all of the interactions.)