回顧問題不定期更新 Study Questions are Made by Prof. Cruz & Prof. Moore from Oberlin College & Conservatory?

Lecture 25: Mitosis/Meiosis/Diploidy

1. Draw out the process of mitosis in haploid cells. To do this, assume the organism has three chromosomes. When drawing out the process of mitosis, make the chromosomes look different in some way—you could make each chromosome a different length, or use different colors for each chromosome, etc.

2. Now, let’s try meiosis:

a) Draw out the process of meiosis for a diploid organism with three sets of homologous chromosomes. Again, come up with a way to differentiate each pair of chromosomes, AND come up with a way to tell apart the homologous chromosomes in each pair—you might use one color for paternal and a different for maternal chromosomes, for example.

b) How many possible combinations of the three parental sets of chromosomes are possible among the gametes of this individual? (You can ignore recombination; just focus on independent assortment.)

3. The questions below all deal with the ABO blood type locus in humans; you can label the alleles at this locus A, B, and O:

a) What are the two possible genotypes for the type A blood phenotype?

b) What is the only possible genotype for the type O blood phenotype?

c) Imagine two parents, one with type B blood and one with type A blood, have four offspring, each of which has a different blood type (i.e., one has type A, one has type B, one has type AB, and one has type O). What is the genotype of each parent?

4. Another blood type locus that is typically determined for humans (in addition to ABO type) is the Rhesus (Rh) factor. The gene for the Rh factor is located on a different chromosome than the ABO gene, and codes for a cell transmembrane protein. There are two common alleles for this gene, one of which codes for a functional version of the protein (in which case they are called Rh+), and the other of which produces a nonfunctional version of the protein (Rh–).

a) Given just the information above, do you think one of the two alleles will be genetically dominant to the other? Why/why not?

b) Which genotype will yield the Rh– phenotype (you can call the alleles + and –)?

c) Imagine an Rh+ parent mates with an Rh– parent, yielding 10 offspring, six of which are Rh+ and four of which are Rh–. Using this information, predict the genotype of the Rh+ parent.

d) Now, let’s get a little more complex. Imagine we determined the ABO blood type for these same two parents. The Rh+ parent has type AB blood, whereas the Rh– parent has type O blood. For each parent, write down all of the genotypes that are possible among the gametes for both loci; for example, A/+ would be one possible genotype for a gamete in the first parent. Keep in mind that the ABO locus and the Rh locus are on different chromosomes. For each parent, it might help to draw two different pairs chromosomes, one with the ABO locus and the other with Rh locus, showing the different alleles present on each.

e) Continuing from the previous question: Across both loci, what are all the possible genotypes and phenotypes in the offspring?

5. Let’s switch gears and think about two loci on the SAME chromosome. Imagine two loci on the same chromosome in a geranium, one of which codes for an enzyme that creates red pigment in the flowers (let’s call it the flower color locus), and the other of which codes for an enzyme that makes leaf trichomes (let’s call this locus the hairy locus). Now, imagine you breed geraniums over several generations in a greenhouse, and one day you notice an individual with white flowers and no leaf hairs. After doing some fancy molecular biology, you determine that the flower color gene has a 2-bp deletion early on in the coding sequence, whereas the hairy gene has a nonsense mutation early on in its coding sequence. Hence, the enzymes at both loci no longer function, and no pigment or hairs are created. Use this information to answer the questions below:

a) At both loci, what must the genotype be in this odd plant? You can use R to designate the normal (wild type) allele at the flower color locus, and r for the non-functional allele, and you can use H to designate the wild type allele at the hairy locus, and h for the non-functional allele.

b) Now imagine you cross (i.e. breed) this white, hairless individual with a wild type individual (i.e., a red flowered, hairy plant). You can assume the wild type individual is homozygous dominant. What will all the offspring have for a genotype and phenotype?

c) Let’s pretend we have a magical compound that prevents crossing over from occurring during meiosis, and that we apply it to the offspring created in question 5b. With respect to the flower color and hairy loci, what are the only two genotypes that will appear in the gametes of these individuals?

d) If we create embryos from the gametes in question 5c, would you ever see red-flowered, hairless plants or white-flowered, hairy plants? Why or why not?

e) Now, go back to the offspring mentioned in question 5b, and let’s imagine that we do NOT apply the magical compound to these plants; i.e. we allow for recombination. If we bred these offspring with each other, would it be possible to see red-flowered, hairless plants or white- flowered, hairy plants among their offspring? Why or why not? (Keep in mind that each of the parental plants makes lots and lots of gametes!)

注意本文集的Study Question都是不定期更新且沒有答案喔~ 有問題的話可以找UP主喔~

離久-張所長