Bio Chapter 8

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.

Chromatids are ____

identical copies of each other if they are part of the same chromosome - Each duplicated chromosome consists of two identical sister chromatids.

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.

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.

Most of the cells life is spent in ___

Interphase

In telophase ____

The chromosomes gather at opposite ends of the cell and lose their distinct shapes. Two new nuclear envelopes will form.

In anaphase ____

The sister chromatids separate into individual chromosomes and are moved apart.

List the phases of mitosis in order

interphase, prophase, metaphase, anaphase, telophase

recombination in meiosis occurs in what phase ?

prophase I

One version of a gene may encode __________, whereas a different version of the same gene may encode __________.

red eyes; white eyes - Different versions of a gene could encode different eye colors. Alternately, they could encode different coat colors.

In humans, the haploid number of chromosomes is 23. Independent assortment has the possibility of producing __________ different gametes.

2^23

In metaphase ___

the spindle is fully formed and chromosomes are lined up in the center

During anaphase II,

Sister chromatids separate and migrate toward opposite poles.

When examining cells in the laboratory, you notice that a particular cell has half as much DNA as the surrounding cells. This observation can be explained if this cell's cell cycle halted at checkpoint _____.

G1 - The cell cycle must have stopped before the S phase; otherwise, the cell would also have twice as much DNA.

Variation occurs when chromosomes are shuffled in _____.

MEIOSIS - result of independent assortment and crossing over

In prophase ____

Microtubules form the spindle - nuclear envelope breaks up

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 functional within any given cell, regardless of the total number of X chromosomes.

Interphase

chromosomes are duplicated

Meiosis differs from mitosis in that:

crossing over only occurs in meiosis

A cell is treated with a drug that prevents the formation of vesicles. Which of the following processes depends on the formation of vesicles and would therefore be blocked?

cytokinesis in a plant cell - the cell plate that ultimately separates one cell into two is formed from coalescing vesicles.

Cytokinesis

division of the cytoplasm

You can determine this is a plant cell rather than an animal cell because it has __________.

formed a cell plate - The cell plate, which divides the cytoplasm in two, forms during telophase of mitosis in a plant cell and can be observed in the center of this image.

During anaphase I,

homologues separate and migrate toward opposite poles

Meisosis : starts w a single diploid cell, ends with ___

4 haploid cells

Polyploidy is involved in which of the following examples?

A normal watermelon has 22 chromosomes but seedless watermelons have 33 chromosomes.

Karyotype:

A picture of all the chromosomes in a cell arranged in pairs

What is the difference between a benign tumor and a malignant tumor?

Benign tumors do not metastasize; malignant tumors do. - Malignant tumors spread from their site of origin to other parts of the bo

Immune system cells enter a resting phase after undergoing mitosis. When activated—for example, by an infection—they can reenter the sequence of events in the cell cycle that leads to cell division. What would be the correct cell cycle sequence of events for these reactivated cells?

G1, S, G2, M

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, the number of chromosomes would be normal, but one chromosome would have two copies of a portion of the chromosome. - Trisomy means three copies of a chromosome; duplication involves a repeated segment of one chromosome.

During binary fission, each copy of the duplicating chromosome moves to opposite ends of the cell. What does this achieve?

It ensures that each daughter cell receives one copy of the chromosome.

When we say that an organism is haploid, we mean that _____

its cells each have one set of chromosomes

In the telophase of mitosis, the mitotic spindle breaks down and the chromatin uncoils. This is essentially the opposite of what happens in _____.

prophase - During prophase we observe the formation of the spindle, the condensation of chromatin, and the disappearance of the nucleolus, which are the opposite events to those occurring during telophase.