CELL REPRODUCTION

Chapter 8

CHROMOSOME STRUCTURE Sec. 8-1 pg. 145

During cell division, the DNA in a eukaryotic cell’s nucleus is coiled into very compact structures called _________________.

Chromosomes are rod-shaped structures made of _________ and ____________________.

Each chromosome is a single DNA molecule associated with proteins.

The DNA in eukaryotic cells wraps tightly around proteins called ___________________.

____________________ help maintain the shape of the chromosome

and aid in the tight packing of DNA.

_____________ proteins are generally involved in controlling the activity of specific regions of the DNA.

Notice that the chromosome consists of two identical halves.

Each half of the chromosome is called a ___________________.

Chromatids form as the DNA makes a copy of itself before cell division.

The constricted area of each chromatid is called a ____________________.

The centromere holds the two chromatids together until they separate during ____________________.

CHROMOSOME NUMBERS pg. 146

Sex Chromosomes and Autosomes pg. 146

Human and animal chromosomes are categorized as either ________________________or _____________________.

_______________________ are chromosomes that determine the sex of an organism, and they may also carry genes for other characteristics.

In humans, ______________________ are either _____ or ______. Normal females have ___________ X chromosomes, and normal males have an X and a Y chromosome.

All of the other chromosomes in an organism are called _______________. Two of the _______________ human chromosomes are _________________, while the remaining ________ chromosomes are __________________.

Every cell of an organism produced by sexual reproduction has ________________ of each autosome.

The organism receives one copy of each autosome from each __________________.

The two copies of each autosome are called ____________________________, or homologues.

Homologous chromosomes are the same size and shape and carry genes for the same traits.

_______________________is a photomicrograph of the chromosomes in a dividing cell found in a normal human.

Diploid and Haploid Cells pg. 147

Cells having two sets of chromosomes are said to be ______________________.

All normal human cells, except reproductive cells (sperm cells and egg cells), are ____________________.

Diploid is commonly abbreviated as _________.

Human sperm cells and egg cells are __________________. These cells contain only one set of chromosomes. Haploid cells have _________ the number of chromosomes that are present in _________________.

Human ______________________ have only one chromosome of each homologous pair and only one sex chromosome.

Haploid is abbreviated as ________.

When a sperm cell (1n) and an egg cell (1n) combine to create the first cell of a new organism, the new cell will be diploid (2n).

CELL DIVISION Section 8-2pg. 148

CELL DIVISION IN PROKARYOTES pg. 148

___________________ is the division of a prokaryotic cell into two offspring cells. Binary fission consists of three general stages, which are outlined in Figure 8-4.

CELL DIVISION IN EUKARYOTES pg. 148

There are two kinds of cell division in eukaryotes.

1. ______________ results in new cells with genetic material that is identical to that of the original cell.

2. _______________ reduces the chromosome number by half in new cells.

The Cell Cycle pg. 149

The _______________ is the repeating set of events that make up

the life of a cell. Cell division is one phase of the cell cycle. The time between cell divisions is called _____________.

Interphase is divided into ___________________ and cell division is divided into two phases, as illustrated in

Figure 8-5.

Interphase pg. 149

During the first stage of interphase called the ____________ offspring cells grow to mature size.

After cells have reached a mature size, they typically proceed into the next phase of interphase, called the _______________. During the S phase, the cell’s ____________ is copied.

The ___________________ represents the time gap following DNA synthesis (S phase) and preceding cell division.

The G2 phase is a time during which the cell prepares for cell division.

Mitosis pg. 149

_______________ is the division of the nucleus, which occurs during cell division. Mitosis is a continuous process that is divided into four phases: prophase, metaphase, anaphase, and telophase.

__________________ is the first phase of mitosis.

The two copies of each chromosome called _____________ stay connected to one another by the centromere.

__________________ appear next to the disappearing nucleus.

In animal cells, each centrosome contains a pair of small, cylindrical bodies called ___________________.

In both animal and plant cells, the centrosomes move toward opposite poles of the cell. As the centrosomes separate, _______________ made of microtubules radiate from the centrosomes in preparation for mitosis.

_________________ is the second phase of mitosis. During metaphase, chromosomes are easier to identify using a microscope than during other phases.

During metaphase, the kinetochore fibers move the chromosomes to the center of the dividing cell. Once in the center of the cell, each chromosome is held in place by the kinetochore fibers.

During __________________, the chromatids of each chromosome separate at the centromere and slowly move, centromere first, toward opposite poles of the dividing cell. When the chromatids separate, they are considered to be individual chromosomes.

____________________ is the fourth phase of mitosis.

After the chromosomes reach opposite ends of the cell, the spindle fibers disassemble and the chromosomes return to a less tightly coiled chromatin state.

A nuclear envelope forms around each set of chromosomes, and nucleolus forms in each of the newly forming cells.

Cytokinesis pg. 151

During telophase, the cytoplasm of the cell divides by a process called cytokinesis.

_________________ is the division of the cytoplasm of the cell.

In animal cells, cytokinesis begins with a pinching inward of the cell membrane midway between the dividing cell’s two poles.

The area of the cell membrane that pinches in and eventually separates the dividing cell into two cells is called the _______________.

In plant cells, the forming of a membrane-bound cell wall called the __________________.

MEIOSIS Section 8-3 pg. 153

Meiosis produces haploid reproductive cells called _____________. Human gametes are sperm cells and egg cells, each of which contains 23 (1n) chromosomes. The fusion of a sperm and an egg results in a zygote that contains 46 (2n) chromosomes.

Meiosis I pg. 153

During prophase I, DNA coils tightly into chromosomes. As in the prophase of mitosis, spindle fibers appear. Then the nucleus and nucleolus disassemble.

The pairing of homologous chromosomes, which does not occur in mitosis, is called _____________________.

Each pair of homologous chromosomes is called a _____________.

In each tetrad, chromatids of the homologous chromosomes are aligned lengthwise so that the genes on one chromosome are adjacent to the corresponding genes on the other chromosome.

Portions of chromatids may break off and attach to adjacent chromatids on the homologous chromosome a process called ____________. This process permits the exchange of genetic material between maternal and paternal chromosomes.

Crossing-over results in ______________________ by producing a new mixture of genetic material.

The random separation of the homologous chromosomes is called _____________________. Independent assortment of the chromosomes results in a random separation of the maternal and paternal chromosomes, which results in genetic variation.

During meiosis I, the original cell produces two new cells. Each new cell contains one chromosome from each homologous pair. The new cells contain half the number of chromosomes of the original cell. However, each new cell contains two copies of the chromosome because the original cell copied its DNA before meiosis I.

During prophase II, spindle fibers form and begin to move the chromosomes toward the midline of the dividing cell. In metaphase II, the chromosomes move to the midline of the dividing cell, facing opposite poles of the dividing cell. In anaphase II, the chromatids separate and move toward opposite poles of the cell. In telophase II, a nuclear membrane forms around the chromosomes in each of the four new cells. Cytokinesis II occurs during telophase II, resulting in four new cells, each of which contains half of the original cell’s number of chromosomes.

Formation of Gametes pg. 155

In animals, meiosis produces __________________________ called ___________, as shown in Figure 8-12. Because only those cells involved in the production of gametes divide by meiosis in animals, meiosis occurs only within their reproductive organs. In humans, meiosis occurs in the __________ and in the______________.

In the testes, meiosis is involved in the production of male gametes known as sperm cells or spermatozoa. In the development of sperm cells, a diploid reproductive cell divides meiotically to form four haploid cells called _____________________. The production of sperm cells is called ____________________.

__________________ is the production of mature egg cells, or ova. During oogenesis, a diploid reproductive cell divides meiotically to produce one mature egg cell (ovum). One egg cell is produced by meiosis. The other three products of meiosis, called ___________________, degenerate.

Asexual and Sexual Reproduction pg.156

_____________________ is the production of offspring from one parent. Asexual reproduction does not usually involve meiosis or the union of gametes. The offspring from asexual reproduction are genetically identical to the parent.

_____________________ is the production of offspring through meiosis and the union of a sperm and an egg. Offspring produced by sexual reproduction are genetically different from the parents because genes are combined in new ways in meiosis.