Deck 3: Reproduction and Chromosometransmission

Question 1

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.

Answer 1

The word "binary fission" means "division into half." It is a common method of reproduction in prokaryotes and is also observed in few single-celled eukaryotes. It begins with single mother cell and gives rise to two daughter cells by the end.
In this process of binary fission, DNA (deoxyribonucleic acid), the genetic material replicates first and segregates apart. Soon after this process, cell undergoes cytokinesis and divides into two daughter cells of same size.
As the genetic material is partitioned equally, the two daughter cells will be genetically identical with each other and also with the mother cell. Unless mutation occurs during DNA replication, the daughter cells remain genetically identical with the mother cell.
The following diagram depicts the process of binary fission:

Question 2

When studying living cells in a laboratory, researchers sometimes use drugs as a way to cause cells to remain in a particular phase of the cell cycle. For example, aphidicolin inhibits DNA synthesis in eukaryotic cells and causes them to remain in the G 1 phase because they cannot replicate their DNA. In what phase of the cell cycle-G 1 , S, G 2 , prophase, metaphase, anaphase, or telophase-would you expect somatic cells to stay if the following types of drug were added
A. A drug that inhibits microtubule formation
B. A drug that allows microtubules to form but prevents them from shortening
C. A drug that inhibits cytokinesis
D. A drug that prevents chromosomal condensation

Answer 2

A drug named aphidicolin inhibits deoxyribonucleic acid synthesis in eukaryotic cells. It is observed that this drug causes DNA to remain in their G 1 phase, so that DNA replication may stop.
If such type of drug is administered, then several changes takes place in G 1 , S, G 2 , prophase, metaphase, anaphase, or telophase of cell cycle. The changes observed in somatic cells when following types of drugs are administered are as follows:
A drug inhibits microtubule formation- In this case drug will affect G 2 phase of the cell cycle that is it could not complete its prophase.
A drug that allows microtubules to form but prevents them from shortening- In this case metaphase is affected and the cell may possibly not enter anaphase.
A drug that inhibits cytokinesis- In this case, cell could not divide into two daughter cells, that is telophase is affected.
A drug that prevents chromosomal condensation- In this case cell's G 2 phase is affected and it could not enter prophase.

Question 3

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

Answer 3

Homolog:
The word "homolog" perfectly refers to the members of a chromosome pair, as the two chromosomes of a pair will be homologous to each other in all aspects. They carry same kind of genes in the same order.
Both the chromosomes of a pair usually are of same size because of the same genes and same order they have. If at any point the homologs differ, it will be only in the alleles the genes carry within them.

Question 4

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 Explain your answer.

Question 5

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

Question 6

In his original studies of Figure 3.18, Morgan first suggested that the original white-eyed male had two copies of the white-eye allele. In this problem, let's assume that he meant the fly was X w Y w instead of X w Y. Are his data in Figure 3.18 consistent with this hypothesis What crosses would need to be made to rule out the possibility that the Y chromosome carries a copy of the eye color gene
FIGURE 3.18 Inheritance pattern of an X-linked trait in fruit flies.

Question 7

With regard to sister chromatids, which phase of mitosis is the organization phase, and which is the separation phase

Question 8

How would you set up crosses to determine if a gene was Y linked versus X linked

Question 9

A species is diploid and has three chromosomes per set. Draw what the chromosomes would look like in the G 1 and G 2 phases of the cell cycle.

Question 10

Occasionally during meiosis, a mistake can happen whereby a gamete may receive zero or two sex chromosomes rather than one. Calvin Bridges made a cross between white-eyed female flies and red-eyed male flies. As you would expect, most of the offspring were red-eyed females and white-eyed males. On rare occasions, however, he found a white-eyed female or a red-eyed male. These rare flies were not due to new gene mutations, but instead were due to mistakes during meiosis in the parent flies. Consider the mechanism of sex determination in fruit flies and propose how this could happen. In your answer, describe the sex chromosome composition of these rare flies.

Question 11

How does the attachment of kinetochore microtubules to the kinetochore differ in metaphase of meiosis I from metaphase of mitosis Discuss what you think would happen if a sister chromatid was not attached to a kinetochore microtubule.

Question 12

Let's suppose that you have karyotyped a female fruit fly with red eyes and found that it has three X chromosomes instead of the normal two. Although you do not know its parents, you do know that this fly came from a mixed culture of flies in which some had red eyes, some had white eyes, and some had eosin eyes. Eosin is an allele of the same gene that has white and red alleles. Eosin is a pale orange color. The red allele is dominant and the white allele is recessive. The expression of the eosin allele, however, depends on the number of copies of the allele. When females have two copies of this allele, they have eosin eyes. When females are heterozygous for the eosin allele and white allele, they have light-eosin eyes. When females are heterozygous for the red allele and the eosin allele, they have red eyes. Males that have a single copy of eosin allele have light-eosin eyes.
You cross this female with a white-eyed male and count the number of offspring. You may assume that this unusual female makes half of its gametes with one X chromosome and half of its gametes with two X chromosomes. The following results were obtained:
* A female offspring can be XXX, XX, or XXY.
Explain the 3:1 ratio between female and male offspring. What was the genotype of the original mother, which had red eyes and three X chromosomes Construct a Punnett square that is consistent with these data.

Question 13

For the following events, specify whether they occur during mitosis, meiosis I, or meiosis II:
A. Separation of conjoined chromatids within a pair of sister chromatids
B. Pairing of homologous chromosomes
C. Alignment of chromatids along the metaphase plate
D. Attachment of sister chromatids to both poles

Question 14

With regard to thickness and length, what do you think the chromosomes would look like if you microscopically examined them during interphase How would that compare with their appearance during metaphase

Question 15

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

Question 16

White-eyed flies have a lower survival rate than red-eyed flies. Based on the data in Figure 3.18, what percentage of white-eyed flies survived compared with red-eyed flies, assuming 100% survival of red-eyed flies
FIGURE 3.18 Inheritance pattern of an X-linked trait in fruit flies.

Question 17

A cell is diploid and contains three chromosomes per set. Draw the arrangement of chromosomes during metaphase of mitosis and metaphase of meiosis I and II. In your drawing, make one set dark and the other lighter.

Question 18

A rare form of dwarfism that also included hearing loss was found to run in a particular family. It is inherited in a dominant manner. It was discovered that an affected individual had one normal copy of chromosome 15 and one abnormal copy of chromosome 15 that was unusually long. How would you determine if the unusually long chromosome 15 was causing this disorder

Question 19

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

Question 20

Discuss why crosses (i.e., the experiments of Mendel) and the microscopic observations of chromosomes during mitosis and meiosis were both needed to deduce the chromosome theory of inheritance.

Question 21

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

Question 22

Female flies with white eyes and miniature wings (both X-linked recessive traits) were crossed to male flies with red eyes and normal wings. On rare occasions, female offspring were produced with white eyes. If we assume these females are due to errors in meiosis, what would be the most likely chromosomal composition of such flies What would be their wing shape

Question 23

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

Question 24

Experimentally, how do you think researchers were able to determine that the Y chromosome causes maleness in mammals, whereas the ratio of X chromosomes to the sets of autosomes causes sex determination in fruit flies

Question 25

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

Question 26

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 Explain your answer.
Question C13
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

Question 27

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

Question 28

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

Question 29

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

Question 30

A diploid species has four chromosomes per set for a total of eight chromosomes in its somatic cells. Draw the cell as it would look in late prophase of meiosis II and prophase of mitosis. Discuss how prophase of meiosis II and prophase of mitosis differ from each other, and explain how the difference originates.

Question 31

Explain why the products of meiosis may not be genetically identical, whereas the products of mitosis are.

Question 32

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

Question 33

List several ways in which telophase appears to be the reverse of prophase and prometaphase.

Question 34

Corn has 10 chromosomes per set, and the sporophyte of the species is diploid. If you performed a karyotype, what is the total number of chromosomes you would expect to see in the following types of cells
A. A leaf cell
B. The sperm nucleus of a pollen grain
C. An endosperm cell after fertilization
D. A root cell

Question 35

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

Question 36

Let's suppose that a gene affecting pigmentation is found on the X chromosome (in mammals or insects) or the Z chromosome (in birds) but not on the Y or W chromosome. It is found on an autosome in bees. This gene exists in two alleles; D (dark), is dominant to d (light). What would be the phenotypic results of crosses between a true-breeding dark female and true-breeding light male, and the reciprocal crosses involving a true-breeding light female and true-breeding dark male, in the following species Refer back to Figure 3.17 for the mechanism of sex determination in these species.
A. Birds
B. Drosophila
C. Bees
D. Humans
FIGURE 3.17 Different mechanisms of sex determination in animals. See text for a description.

Question 37

Describe the cellular differences between male and female gametes.

Question 38

At puberty, the testes contain a finite number of cells and produce an enormous number of sperm cells during the life span of a male. Explain why testes do not run out of spermatogonial cells.

Question 39

Describe the timing of meiosis I and II during human oogenesis.

Question 40

Three genes ( A , B , and C ) are found on three different chromosomes. For the following diploid genotypes, describe all of the possible gamete combinations.
A. Aa Bb Cc
B. AA Bb CC
C. Aa BB Cc
D. Aa bb cc

Question 41

A phenotypically normal woman with an abnormally long chromosome 13 (and a normal homolog of chromosome 13) marries a phenotypically normal man with an abnormally short chromosome 11 (and a normal homolog of chromosome 11). What is the probability of producing an offspring that will have both a long chromosome 13 and a short chromosome 11 If such a child is produced, what is the probability that this child would eventually pass both abnormal chromosomes to one of his or her offspring

Question 42

Assuming that such a fly would be viable, what would be the sex of a fruit fly with the following chromosomal composition
A. One X chromosome and two sets of autosomes
B. Two X chromosomes, one Y chromosome, and two sets of autosomes
C. Two X chromosomes and four sets of autosomes
D. Four X chromosomes, two Y chromosomes, and four sets of autosomes

Question 43

What would be the sex of a human with the following numbers of sex chromosomes
A. XXX
B. X (also described as X0)
C. XYY
D. XXY