Pierce's Genetics: Chapter 2
What are three essential elements required for a chromosome to function?
A centromere, a pair of telomeres, and an origin of replication
eukaryote
A eukaryote has a compartmentalized cell structure having components bounded by intracellular membranes; eukaryotes may be unicellular or multicellular
nucleus
A nuclear envelop surrounds the genetic material to form a nucleus and separates the DNA from the other cellular contents
prokaryote
A prokaryote is a unicellular organism with a relatively simple cell structure
Prokaryotic cells and eukaryotic cells
A prokaryotic cell possesses a simple structure, with no nuclear envelope and usually a single, circular chromosome. A eukaryotic cell possesses a more complex structure, with a nucleus and multiple linear chromosomes consisting of DNA complexed to histone proteins.
anaphase I
Anaphase I is marked by the separation of homologous chromosomes. The two chromosomes of a homologous pair are pulled toward opposite poles.
anaphase
Anaphase begins when the sister chromatids separate and move toward opposite spindle poles. After the chromatids have separated, each is considered a separate chromosome.
What does cell reproduction require?
Cell reproduction requires the copying of the genetic material, separation of the copies, and cell division.
How do cells reproduce?
Cells reproduce by copying and separating their genetic information and then dividing. Because eukaryotes possess multiple chromosomes, mechanisms exist to ensure that each new cell receives one copy of each chromosome. Most eukaryotic cells are diploid, and their two chromosome sets can be arranged in homologous pairs. Haploid cells contain a single set of chromosomes.
haploid
Cells with a single set of chromosomes are haploid. A haploid cell has only one copy of each gene.
recombination
Crossing over is the basis for intrachromosomal recombination, creating new combinations of alleles on a chromatid
prometaphase
Disintegration of the nuclear membrane marks the start of prometaphase. Spindle microtubules, which until now have been outside the nucleus, enter the nuclear region.
prophase
During interphase, the chromosomes are relaxed and are visible only as diffuse chromatin, but they condense during prophase, becoming visible under a light microscope. Each chromosome possesses two chromatids because the chromosome was duplicated in the preceding S phase.
metaphase
During metaphase, the chromosomes become arranged in a single plane, the metaphase plate, between the two centrosomes. The centrosomes, now at opposite ends of the cell with microtubules radiating outward and meeting in the middle of the cell, center at the spindle poles.
bivalent
Each homologous pair of synapsed chromosomes consists of four chromatids called a bivalent or tetrad
tetrad
Each homologous pair of synapsed chromosomes consists of four chromatids called a bivalent or tetrad
secondary spermatocyte
Each primary spermatocyte completes meiosis I, giving rise to two haploid secondary spermatocytes
List several characteristics that eubacteria and archaea have in common and that distinguish them from eukaryotes.
Eubacteria and archaea are prokaryotes. They differ from eukaryotes in possessing no nucleus, a genome that usually consists of a single, circular chromosome, and a small amount of DNA.
synapsis
First, the chromosomes condense, pair up, and begin synapsis, a very close pairing association
histone
In eukaryotes, DNA is closely associated with a special class of proteins, the histones, to form tightly packed chromosomes
telophase II
In telophase II, the chromosomes arrive at the spindle poles, a nuclear envelope re-forms around the chromosomes, and the cytoplasm divides. The chromosomes relax and are no longer visible.
Reproduction of prokaryotic and eukaryotic cells?
In a prokaryotic cell, the single chromosome replicates, each copy moves toward opposite sides of the cell, and the cell divides. In eukaryotic cells, reproduction is more complex than in prokaryotic cells, requiring mitosis and meiosis to ensure that a complete set of genetic information is transferred to each new cell.
anaphase II
In anaphase II, the kinetochores of the sister chromatids separate and the chromatids are pulled to opposite poles. Each chromatid is now a distinct chromosome
Haploid production in animals?
In animals, a diploid spermatogonium undergoes meiosis to produce four haploid sperm cells. A diploid oogonium undergoes meiosis to produce one large haploid ovum and one or more smaller polar bodies.
Where are chromosomes in eukaryotic cells?
In eukaryotic cells, chromosomes are typically found in homologous pairs. Each functional chromosome consists of a centromere, telomeres, and multiple origins of replication. After a chromosome has been copied, the two copies remain attached at the centromere, forming sister chromatids
secondary oocyte
In oogenesis, cytokinesis is unequal: most of the cytoplasm is allocated to one of the two haploid cells, the secondary oocyte.
Haploid production in plants?
In plants, a diploid microsporocyte in the stamen undergoes meiosis to produce four pollen grains, each with two haploid sperm cells. In the ovary, a diploid megasporocyte undergoes meiosis to produce eight haploid nuclei, one of which forms the egg.
telophase I
In telophase I, the chromosomes arrive at the spindle poles and the cytoplasm divides.
How are haploid cells produced?
In the stamen of a flowering plant, meiosis produces haploid microspores that divide mitotically to produce haploid sperm in a pollen grain. Within the ovary, meiosis produces four haploid megaspores, only one of which divides mitotically three times to produce eight haploid nuclei.After pollination, one sperm fertilizes the egg cell, producing a diploid zygote; the other fuses with two nuclei to form the endosperm.
What undergoes meiosis in the testes?
In the testes, a diploid spermatogonium undergoes meiosis, producing a total of four haploid sperm cells. In the ovary, a diploid oogonium undergoes meiosis to produce a single large ovum and smaller polar bodies that normally disintegrate.
What processes does meiosis consist?
Meiosis consists of two distinct processes: meiosis I and meiosis II. Meiosis (usually) produces four haploid cells that are genetically variable.The two mechanisms responsible for genetic variation are crossing over and the random distribution of maternal and paternal chromosomes.
metaphase I
Metaphase I is initiated when homologous pairs of chromosomes align along the metaphase plate (
What are the results of mitosis?
Mitosis usually results in the production of two genetically identical cells.
What are the classification of organisms?
Organisms are classified as prokaryotes or eukaryotes, and prokaryotes consist of archaea and eubacteria. A prokaryote is a unicellular organism that lacks a nucleus, its DNA is not complexed to histone proteins, and its genome is usually a single chromosome. Eukaryotes are either unicellular or multicellular, their cells possess a nucleus, their DNA is complexed to histone proteins, and their genomes consist of multiple chromosomes
origin of replication
Origins of replication are the sites where DNA synthesis begins; they are not easily observed by microscopy. In preparation for cell division, each chromosome replicates, making a copy of itself, as already mentioned.
checkpoint
Progression through the cell cycle is regulated at key transition points called checkpoints.
prophase I
Prophase I is a lengthy stage in which the chromosomes form homologous pairs and crossing over takes place
meiosis
Sexual reproduction consists of two processes. The first is meiosis, which leads to gametes in which chromosome number is reduced by half.
Sexual reproduction?
Sexual reproduction produces genetically variable progeny and allows for accelerated evolution. It includes meiosis, in which haploid sex cells are produced, and fertilization, the fusion of sex cells.Meiosis includes two cell divisions. In meiosis I, crossing over takes place and homologous chromosomes separate. In meiosis II, chromatids separate.
What are sister chromatids?
Sister chromatids are copies of a chromosome held together at the centromere. Functional chromosomes contain centromeres, telomeres, and origins of replication. The kinetochore is the point of attachment for the spindle microtubules; telomeres are the stabilizing ends of a chromosome; origins of replication are sites where DNA synthesis begins
telomere
Telomeres are the natural ends, the tips, of a linear chromosome. they serve to stabilize the chromosome ends.
telophase
Telophase is marked by the arrival of the chromosomes at the spindle poles. The nuclear membrane reforms around each set of chromosomes, producing two separate nuclei within the cell. The
second polar body
The smaller cell is the second polar body.
What are the active cell-cycle phases?
The active cell-cycle phases are interphase and the M phase. Interphase consists of G1, S, and G2. In G1, the cell grows and prepares for cell division; in the S phase, DNA synthesis takes place; in G2, other biochemical events necessary for cell division take place. Some cells enter a quiescent phase called G0. The M phase includes mitosis and cytokinesis and is divided into prophase, prometaphase, metaphase, anaphase, and telophase.
What are the stages of cell division?
The cell cycle consists of the stages through which a eukaryotic cell passes between cell divisions. It consists of (1) interphase, in which the cell grows and prepares for division and (2) the M phase, in which nuclear and cell division take place. The M phase consists of (1) mitosis, the process of nuclear division, and (2) cytokinesis, the division of the cytoplasm.
interphase
The cell cycle consists of two major phases. The first is interphase, the period between cell divisions, in which the cell grows, develops, and prepares for cell division.
cell cycle
The cell cycle is the life story of a cell, the stages through which it passes from one division to the next.
crossing over
The chromosomes become shorter and thicker, and a three-part synaptonemal complex develops between homologous chromosomes. Crossing over takes place, in which homologous chromosomes exchange genetic information.
megasporocyte
The female part of the flower, the ovary, contains diploid cells called megasporocytes,
ovum
The larger cell, which acquires most of the cytoplasm, is the ovum, the mature female gamete.
microsporocyte
The male part of the flower, the stamen, contains diploid reproductive cells called microsporocytes.
interkinesis
The period between meiosis I and meiosis II is interkinesis, in which the nuclear membrane re-forms around the chromosomes clustered at each pole, the spindle breaks down, and the chromosomes relax
oogenesis
The production of gametes in a female animal, called oogenesis, begins much like spermatogenesis
spermatogenesis
The production of gametes in a male animal, called spermatogenesis, takes place in the testes
M phase
The second is the M phase (mitotic phase), the period of active cell division. The M phase includes mitosis.
fertilization
The second process is fertilization, in which two haploid gametes fuse and restore chromosome number to its original diploid value.
first polar body
The smaller cell, which contains half of the chromosomes but only a small part of the cytoplasm, is called the first polar body; it may or may not divide further.
homologous pair
The two chromosomes of a homologous pair are usually alike in structure and size, and each carries genetic information for the same set of hereditary characteristics.
Result of meiosis?
The usual result of meiosis is the production of four haploid cells that are genetically variable. Genetic variation in meiosis is produced by crossing over and by the random distribution of maternal and paternal chromosomes.
spermatogonium
There, diploid primordial germ cells divide mitotically to produce diploid cells called spermatogonia (
metaphase II
These cells move directly from cytokinesis into metaphase II, which is similar to metaphase of mitosis: the individual chromosomes line up on the metaphase plate, with the sister chromatids facing opposite poles.
prophase II
These cells then pass through prophase II, in which the events of interkinesis are reversed: the chromosomes recondense, the spindle reforms, and the nuclear envelope once again breaks down
sister chromatid
These two initially identical copies, called sister chromatids, are held together at the centromere (see Figure 2.5). Each sister chromatid consists of a single molecule of DNA.
chromatin
This complex of DNA and histone proteins is termed chromatin, which is the stuff of eukaryotic chromosomes
primary oocyte
When they enter prophase I, these still-diploid cells are called primary oocytes. Each primary oocyte completes meiosis I and divides.
oogonium
Within the ovaries, diploid primordial germ cells divide mitotically to produce oogonia
primary spermatocyte
a primary spermatocyte, the cell is still diploid because the homologous chromosomes have not yet separated.
Which is the correct order of stages in the cell cycle? a. G1, S, prophase, metaphase, anaphase b. S, G1, prophase, metaphase, anaphase c. Prophase, S, G1, metaphase, anaphase d. S, G1, anaphase, prophase, metaphase
a. G1, S, prophase, metaphase, anaphase
archaea
ancient bacteria
Diploid cells have a. two chromosomes. b. two sets of chromosomes. c. one set of chromosomes. d. two pairs of homologous chromosomes.
b. two sets of chromosomes.
cytokinesis
cytoplasmic division
A secondary spermatocyte has 12 chromosomes. How many chromosomes will be found in the primary spermatocyte that gave rise to it? a. 6 b. 12 c. 18 d. 24
d. 24
Which structure is diploid? a. Microspore c. Megaspore b. Egg d. Microsporocyte
d. Microsporocyte
Which of the following events takes place in meiosis II but not meiosis I? a. Crossing over b. Contraction of chromosomes c. Separation of homologous chromosomes d. Separation of chromatids
d. Separation of chromatids
megaspore
megasporocytes, each of which undergoes meiosis to produce four haploid megaspores
microspore
microsporocytes, each of which undergoes meiosis to produce four haploid microspores
diploid
most cells carry two sets of genetic information; these cells are diploid
mitosis
the process of nuclear division
eubacteria
true bacteria
spermatid
two haploid secondary spermatocytes that then undergo meiosis II, with each producing two haploid spermatids. Thus
