Chapter 8 Section Reviews

8) Explain how it might happen that a human offspring with 47 chromosomes could be produced.

If a gamete with 24 chromosomes fertilized (or was fertilized by) one with the normal 23, the zygote would have 47.

8) What would result if chromosomes did not replicate during interphase?

If chromosomes did not replicate during interphase, each new cell would receive only half the information needed to function properly.

7) What would happen if cytokinesis took place before mitosis?

If cytokinesis took place before mitosis, chromosomes would be divided haphazardly, resulting in a defective cell.

6) Which type of molecule controls the cell cycle?

Although ultimately controlled by DNA, the cell cycle is specifically controlled by a number of proteins.

4) During which phase of mitosis do chromatids separate to become chromosomes?

Chromatids separate to become chromosomes at anaphase.

3) Explain the role of crossing-over in ensuring genetic variation.

Crossing-over permits the exchange of genetic material between maternal and paternal chromosomes, producing a new combination of genes

2) How does anaphase I in meiosis differ from anaphase in mitosis?

In anaphase I of mitosis, sister chromatids separate. In anaphase I of meiosis, homologous pairs separate, but sister chromatids do not.

5) Explain the main difference between cytokinesis in animal cells and cytokinesis in plant cells

In animal cells, cytokinesis begins with a pinching inward of the cell membrane midway between the cell's two poles. This cleavage furrow separates the dividing cell into two cells. In plant cells, vesicles formed by the Golgi apparatus fuse at the midline of the dividing cell, forming a cell plate. The cell plate will eventually separate the cell into two new cells.

6) Why is meiosis essential to sexual reproduction?

Meiosis ensures that the chromosome number in a zygote will not be doubled at fertilization. In addition, the resulting offspring are genetically different from either parent.

1) How do the end products of meiosis differ from the end products of mitosis?

Meiosis produces four haploid cells, and mitosis produces two diploid cells

3) During which of the phases of interphase does an offspring cell grow to mature size?

Most cellular growth occurs during the G1 phase of interphase.

1) Name the process by which prokaryotic cells divide.

Prokaryotic cells divide by binary fission.

7) Explain why the chromosomes in the haploid cells that are produced by meiosis I look different from those produced by meiosis II.

Sister chromatids are still together at the end of meiosis I. During meiosis II the sister chromatids separate, forming "single" chromosomes.

5) Describe the differences between spermatogenesis and oogenesis.

Spermatogenesis produces four sperm cells with equal parts of the original cell's cytoplasm. Oogenesis produces one egg cell with most of the original cell's cytoplasm, and three other cells become polar bodies that will eventually degenerate.

4) During which stage of meiosis is the diploid number of chromosomes reduced to the haploid number of chromosomes?

Telophase I.

9) Why are individual chromosomes more difficult to see during interphase than during mitosis?

The chromosomes undergo extreme coiling at the end of interphase and beginning of prophase to prepare for cell division, and thus allowing them to become more visible.

9) In humans, the egg is larger than the sperm. Explain how it is possible that a child inherits equally from its mother and father.

The difference in size is due to the egg gaining the majority of the original cell's cytoplasm, and the sperm getting an equal share of cytoplasm among 4 sperm cells. Hereditary is carried primarily in the DNA which is not the same as the cytoplasm.

2) What is the name of the process by which the cell's cytoplasm divides?

The division of the cytoplasm is called cytokinesis.