BIO306-Exam 1 Chapter 3
What would be the sex of a human with each of the following sets of sex chromosomes? XXY
Male; the Y chromosome determines maleness.
What would be the sex of a human with each of the following sets of sex chromosomes? XYY
Male; the Y chromosome determines maleness.
With regard to sister chromatids, which phase of mitosis is the organization phase, and which is the separation phase?
Metaphase is the organization phase and anaphase is the separation phase
What is a sister chromatid? Are sister chromatids genetically similar or identical? Explain.
Sister chromatids are identical copies derived from the replication of a parental chromosome. They remain attached to each other at the centromere. They are genetically identical, barring rare mutations and crossing over with homologous chromosomes.
Assuming that such a fly would be viable, what would be the sex of a fruit fly with the following chromosomal composition? One X chromosome and two sets of autosomes
The fly is a male because the ratio of X chromosomes to sets of autosomes is 1/2, or 0.5.
A cell has four pairs of chromosomes. Assuming that crossing over does not occur, what is the probability that a gamete will contain all of the paternal chromosomes? If n equals the number of chromosomes in a set, which of the following expressions can be used to calculate the probability that a gamete will receive all of the paternal chromosomes: (1/2)^n, (1/2)^n-1, or n^1/2?
(1/2)^n = (1/2)^4 = 1/16 or 6.25%
Three genes (A,B, and C) are found on three different chromosomes. For the following diploid genotypes, describe all of the possible gamete combinations. Aa Bb Cc
A B C, A B c, A b C, A b c, a B C, a b C, a B c, a b c
Three genes (A,B, and C) are found on three different chromosomes. For the following diploid genotypes, describe all of the possible gamete combinations. Aa BB Cc
A B C, A B c, a B C, a B c
Three genes (A,B, and C) are found on three different chromosomes. For the following diploid genotypes, describe all of the possible gamete combinations. AA Bb CC
A B C, A b C
Three genes (A,B, and C) are found on three different chromosomes. For the following diploid genotypes, describe all of the possible gamete combinations. Aa bb cc
A b c, a b c
Eukaryotic cells must sort their chromosomes during mitosis so each daughter cell receives the correct number of chromosomes. Why don't bacteria need to sort their chromosomes?
Bacteria do not need to sort their chromosomes because they only have one type of chromosome. Though not discussed in the text, the attachment of the two copies of the chromosomes to the cell membrane prior to cell division also helps to ensure that each daughter cell receives one copy.
The period between meiosis I and meiosis II is called interphase II. Does DNA replication take place during interphase II?
DNA replication does not take place during interphase II. The chromosomes at the end of telophase I have already replicated (i.e. they are found in pairs of sister chromatids). During meiosis II, the sister chromatids separate from each other, yielding individual chromosomes.
For the following events, specify whether they occur during mitosis, meiosis I, or meiosis II: Alignment of chromatids along the metaphase plate.
During all
Why is it necessary for the chromosomes to condense during mitosis and meiosis? What do you think might happen if the chromosomes were not condensed?
During interphase, the chromosomes are greatly extended. In this conformation, they might get tangled up with each other and not sort properly during meiosis and mitosis. The condensation process probably occurs so that the chromosomes easily align along the metaphase plate during metaphase without getting tangled up.
With regard to thickness and length, what do you think chromosomes would look like if you microscopically examined them during interphase? How would that compare with their appearance during metaphase?
During interphase, the chromosomes are longer, thinner, and much harder to see. In metaphase, they are highly condensed, which makes them thicker and shorter.
For the following events, specify whether they occur during mitosis, meiosis I, or meiosis II: Pairing of homologous chromosomes.
During meiosis I
For the following events, specify whether they occur during mitosis, meiosis I, or meiosis II: Attachment of sister chromatids to both poles.
During mitosis and meiosis II
For the following events, specify whether they occur during mitosis, meiosis I, or meiosis II: Separation of conjoined chromatids within a pair of sister chromatids.
During mitosis and meiosis II
What would be the sex of a human with each of the following sets of sex chromosomes? X(also described as Xo)
Female; there are no Y chromosomes.
What would be the sex of a human with each of the following sets of sex chromosomes? XXX
Female; there are no Y chromosomes.
How does the attachment of the kinetochore microtubules to the kinetochore differ in metaphase of meiosis I and metaphase of mitosis? Discuss what you think would happen if a sister chromatid was not attached to a kinetochore microtubule.
In metaphase I of meiosis, each pair of chromatids is attached to only one pole via the kinetochore microtubules. In metaphase of mitosis, there are two attachments (i.e. to both poles). If the attachment was lost, a chromosome would not migrate to a pole and may not become enclosed in a nuclear membrane after telophase. If left out in the cytosol, it would eventually be degraded.
The arrangement of homologs during metaphase of meiosis I is a random process. In your own words, explain what this means.
It means that the maternally derived and paternally derived chromosomes are randomly aligned along the metaphase plate during metaphase I.
A eukaryotic cell is diploid containing 10 chromosomes (5 in each set). For mitosis and meiosis, how many daughter cells would be produced, and how many chromosomes would each one contain?
Mitosis--two diploid cells containing 10 chromosomes each (two complete sets). Meiosis--four haploid cells containing 5 chromosomes each (one complete set)
In Morgan's experiments which result do you think is the most convincing piece of evidence pointing to x-linkage of the eye color gene?
Perhaps the most convincing observation was that all of the white-eyed flies of the F2 generation were males. This suggests a link between sex determination and the inheritance of this trait. Because sex determination in fruit flies is determined by the number of X chromosomes, this outcome suggests a relationship between the inheritance of the X chromosome and the inheritance of this trait.
Assuming that such a fly would be viable, what would be the sex of a fruit fly with the following chromosomal composition? Four X chromosomes, two Y chromosomes, and four sets of autosomes
The fly is female because the ratio of X chromosomes to sets of autosomes is 1.0.
Assuming that such a fly would be viable, what would be the sex of a fruit fly with the following chromosomal composition? Two X chromosomes, one Y chromosome, and two sets of autosomes
The fly is female because the ratio of X chromosomes to sets of autosomes is 1.0.
Assuming that such a fly would be viable, what would be the sex of a fruit fly with the following chromosomal composition? Two X chromosomes and four sets of autosomes
The fly is male because the ratio of X chromosomes to sets of autosomes is 0.5.
The arctic fox has 50 chromosomes (25 per set), and the common red fox has 38 chromosomes (19 per set). These species can interbreed to produce viable but infertile offspring. How many chromosomes would the offspring have? What problems do you think may occur during meiosis that would explain the offspring's infertility?
The hybrid offspring would have 44 chromosomes (i.e. 25+19). The reason the infertility is because each chromosome does not have a homologous partner. Therefore, the chromosomes cannot properly pair during metaphase I, and the gametes do not receive one copy of each homolog. Gametes will be missing certain chromosomes, which makes them infertile.
With regard to question c13, how would the phenomenon of crossing over affect the results? In other words, would the probability of a gamete inheriting only paternal chromosomes be higher or lower?
The probability of inheriting only paternal chromosomes would be much lower because pieces of maternal chromosomes would be mixed with the paternal chromosomes. Therefore, inheriting a chromosome that was completely paternally derived would be unlikely.
Explain why the products of meiosis ay not be genetically identical, whereas the products of mitosis are.
The products of meiosis have only one copy of each type of chromosome. For example, one human gamete may contain the paternally derived copy of chromosome 11, whereas a different gamete may contain the maternally derived copy of chromosome 11. These two homologs may carry different alleles of the same genes and therefore are not identical. In contrast, mitosis produces genetically identical daughter cells that have both copies of all the pairs of homologous chromosomes.
Describe the key events during meiosis that result in a 50% reduction in the amount of genetic material per cell.
The reduction occurs because there is a single DNA replication event but two cell divisions. Because of the nature of separation during anaphase I, each cell receives one copy of each type of chromosome.
What is a homolog? With regard to genes and alleles, how are homologs similar to and different from each other?
The term homolog refers to the members of a chromosome pair. Homologs are usually the same size and carry the same types and order of genes. They may differ in that the genes they carry may be different alleles.
If a diploid cell contains six chromosomes (i.e. three per set), how many possible random arrangements of homologs could occur during metaphase of meiosis I?
There are three pairs of chromosomes. The number of different, random alignments equals 2^n, where n equals the number of chromosomes per set. So the possible number of arrangements equals 2^3, which is 8.
The process of binary fission begins with a single mother cell and ends with two daughter cells. Would you expect the mother and daughter cells to be genetically identical? Explain why or why not.
They are genetically identical, barring rare mutations, because they receive identical copies of the genetic material from the mother cell.
Nine-banded armadillos almost always give birth to four offspring that are genetically identical quadruplets. Explain how you think this happens
To produce identical quadruplets, fertilization begins with one sperm and one egg cell. This fertilized egg then could divide twice by mitosis to produce four genetically identical cells. These four cells could then separate from each other to begin the lives of four distinct individuals. Another possibility is that mitosis could produce two cells that separate from each other. These two cells could then divide by mitosis to produce two pairs of cells, which could also separate to produce four individual cells.
Discuss why crosses (ie the experiments of Mendel) and the microscopic observations of chromosomes during mitosis and meiosis were both needed to deduce the chromosome theory of inheritance.
You need to make crosses to understand the pattern of inheritance of traits (determined by genes) from parents to offspring. And you need to microscopically examine cells to understand the pattern of transmission of chromosomes. The correlation between the pattern of transmission of chromosomes during meiosis, and Mendel's laws of segregation and independent assortment, is what led to the chromosome theory of inheritance.
