BioChp8

Inbreeding has a number of interesting effects. For one, highly inbred strains (varieties) may carry identical forms of every gene. Mice have 40 chromosomes in their diploid (2n) set. How many genetically distinct kinds of gametes (gametes with different genetic characteristics) could be produced through meiosis in an inbred strain where there are identical forms of every gene?

1

During binary fission, the replicated bacterial chromosome attaches to the plasma membrane by specialized anchor proteins. What is the purpose of this attachment between chromosome and membrane?

It ensures the separation of the replicated chromosomes as new membrane is made.

Trisomy for most autosomes is fatal, yet trisomy or even tetrasomy (four copies) of the X chromosome is not. What is the explanation for this difference?

Only one copy of the X chromosome is active, regardless of the total number of X chromosomes.

What would be the immediate consequence of destroying a cell's centrosomes?

The mitotic spindle would not form.

The M phase of mitosis and M phase of meiosis both occur after interphase. However, the two processes differ in the arrangement and behavior of their chromosomes. How?

The pairing up of homologous chromosomes and crossing over only occur during meiosis.

Within one chromosome, what is the relationship between the sequence of bases in DNA of one sister chromatid compared to the other?

The sequences are identical.

During meiosis I, homologous chromosomes form a tetrad. What does this accomplish?

This brings the chromosomes into alignment so that crossing over can create new combinations of genes present on a single chromosome.

Although in humans there are 22 pairs of autosomal chromosomes, only three different chromosomal trisomies are commonly seen in newborns. Of the remaining 19 autosomes, many trisomies have not been seen in newborns. Why not?

Trisomy for the other autosomal chromosomes is often lethal, and the affected embryos are miscarried.

In many organisms, including humans, chromosomes are found in homologous pairs. Homologous chromosomes _____.

are identical in the arrangement of their genes, but some versions of the genes may differ between the chromosomes

Asexual and sexual reproduction differ in that sexual reproduction _____.

can produce great variation among the offspring

A benign and a malignant tumor differ in that _____.

cells of a benign tumor remain within the tumor, whereas cells of a malignant tumor can spread to other body tissues

A cell is treated with a drug that prevents the formation of intracellular (within the cell) vesicles. Which of the following processes would be blocked?

cytokinesis in a plant cell

Baker's yeast is an organism with 32 chromosomes that can perform asexual or sexual reproduction and exist as both a diploid and haploid cell. After meiosis, how many chromosomes will be present in each cell?

16

If we assume that crossing over does not occur, how many different combinations of chromosomes are possible in a zygote derived from diploid parents who have 3 pairs of of chromosomes?

64 Correct. Each gamete can have eight different combinations of parental chromosomes (2n, or 23). There are 8 × 8 = 64 different combinations possible for the zygote.

In the laboratory, cancer cells fail to show density-dependent inhibition of growth in cell culture. What is one explanation that could account for this?

Cancer cells continuously secrete growth factors into the cell culture medium.

Which of the following statements correctly describes the timing of DNA synthesis?

DNA is synthesized in the S phase of interphase.

Scientists commonly choose white blood cells that are going through mitosis to prepare karyotypes. Why?

During mitosis, chromosomes are more condensed than during interphase.

When examining cells in the laboratory, you notice that a particular cell has half as much DNA as the surrounding cells. It appears that this cell's cell cycle halted at checkpoint _____.

G1

You suspect that a serious developmental disorder is due to a chromosome abnormality and prepare a karyotype from an affected individual. In analyzing the karyotype, how could you distinguish trisomy from a chromosome structural defect such as a duplication?

In trisomy there would be one extra chromosome; in a duplication, one chromosome would have two copies of a portion of the chromosome.

In theory, when a nondisjunction for chromosome 18 occurs during meiosis I, four gametes can be produced. If these gametes are fertilized with unaffected gametes from the second parent, what observations would you make concerning the resulting embryos?

Two of the embryos will be trisomic for chromosome 18, and two will contain a single copy of chromosome 18.

When forming buds, hydras _____.

divide by mitosis

At the conclusion of meiosis I, the daughter cells are _____.

haploid and the sister chromatids are joined

Consider the process by which bacterial populations grow. What process performs a similar function in humans?

mitosis

In meiosis II, _____.

sister chromatids are separated

During mitosis, the chromosomes move because _____.

they attach to a dynamic, precisely regulated mitotic spindle

In a cell with eight chromosomes, one chiasma develops during meiosis I in only one particular pair of homologs. How many recombinant chromosomes will there be at the completion of meiosis II?

two