Chapter 3 1W

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, anaphase

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%

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?

2^3, which is 8.

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?

44 chromosomes (i.e. 25+19). each chromosome does not have a homologous partner.

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.

For the following events, specify whether they occur during mitosis, meiosis I, or meiosis II: Alignment of chromatids along the metaphase plate.

During all

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.

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)

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.

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. In contrast, mitosis produces genetically identical daughter cells that have both copies of all the pairs of homologous chromosomes.

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.

Describe the key events during meiosis that result in a 50% reduction in the amount of genetic material per cell.

a single DNA replication event but two cell divisions.

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?

all of the white-eyed flies of the F2 generation were males.

Nine-banded armadillos almost always give birth to four offspring that are genetically identical quadruplets. Explain how you think this happens

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.

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.

genetically identical

What is a sister chromatid? Are sister chromatids genetically similar or identical? Explain.

identical copies derived from the replication of a parental chromosome. genetically identical

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.

metaphase I: one pole via the kinetochore microtubules. metaphase: two attachments (i.e. to both poles). If the attachment was lost, a chromosome would not migrate to a pole

The period between meiosis I and meiosis II is called interphase II. Does DNA replication take place during interphase II?

no

The arrangement of homologs during metaphase of meiosis I is a random process. In your own words, explain what this means.

the maternally derived and paternally derived chromosomes are randomly aligned along the metaphase plate during metaphase I.

What is a homolog? With regard to genes and alleles, how are homologs similar to and different from each other?

the members of a chromosome pair. same size and carry the same types and order of genes. differ in that the genes they carry may be different alleles.

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?

they might get tangled up with each other and not sort properly during meiosis and mitosis. T easily align along the metaphase plate