Chap 2: Chromosome Transmission During Cell Division and Sexual Reproduction

chromosomes

the structures within living cells that contain the genetic material. Genes are physically located within the chromosomes. Biochemically, a chromosome contains a very long segment of DNA, which is the genetic material, and proteins, which are bound to the DNA and provide it with an organized structure.

chromatin

the complex of DNA and proteins that is found within eukaryotic chromosomes.

prokaryotes

another name for bacteria and archaea. The term refers to the observation that their chromosomes are not contained within a membrane-bound nucleus in the cell.

nucleoid

a darkly staining region that contains the genetic material of mitochondria, chloroplasts, or bacteria.

eukaryotes

one of the three domains of life. A defining feature of these organisms is that their cells contain a membrane-bound nucleus.

organelle

a specialized structure within a cell that is surrounded by a single or double membrane or caused by liquid-liquid phase separation.

nucleus

a membrane-bound organelle in eukaryotic cells where the chromosomes are found.

cytogenetics

the field of genetics that involves the microscopic examination of chromosomes

cytogeneticist

a scientist who studies chromosomes under the microscope

somatic cell

any cell of the body except for gametes and germ-line cells that give rise to gametes.

gamete

a reproductive cell (usually haploid) that can unite with another reproductive cell to create a zygote. Sperm and egg cells

germ cells

the gametes (i.e., sperm and egg cells).

karyotype

a photographic representation of all the chromosomes within a cell. It reveals how many chromosomes are found within an actively dividing somatic cell

diploid

an organism or cell that contains two sets of chromosomes.

homologs

structures that are similar to each other due to descent from a common ancestor.

allele

an alternative form of a specific gene.

homozygous

describes a diploid individual that has two identical alleles of a particular gene.

heterozygous

describes a diploid individual that has different versions (i.e., two different alleles) of the same gene.

locus (p. loci)

the site within a genetic map where a specific gene or other DNA segment is found

asexual reproduction

a form of reproduction that does not involve the union of gametes; at the cellular level, a preexisting cell divides to produce two new cells.

multicellularity

consisting of more than one cell.

binary fission

the physical process whereby a bacterial cell divides into two daughter cells. During this event, the two daughter cells become separated by the formation of a septum.

cell cycle

in eukaryotic cells, a series of stages through which a cell progresses in order to divide. The phases are G for gap, S for synthesis (of the genetic material), and M for mitosis (which includes cytokinesis). There are two G phases, G₁ and G₂.

interphase

the series of phases G₁, S, and G₂, during which a eukaryotic cell spends most of its life.

G1 phase

a phase of the eukaryotic cell cycle in which a cell may prepare to divide, depending on the cell type and conditions.

restriction point

a point in the G₁ phase of the cell cycle at which a cell becomes committed to divide.

S phase

a phase of the eukaryotic cell cycle, between the G₁ and G₂ phases, during which a cell replicates its chromosomes.

chromatids

following chromosomal replication in eukaryotes, the two copies that remain attached to each other in the form of sister chromatids.

sister chromatids (dyad)

pairs of replicated chromosomes that are attached to each other at the centromere. Sister chromatids are genetically identical.

monad

a single chromatid within a dyad.

kinetochore

a protein complex bound to a centromere of a chromosome during meiosis and mitosis.

G2 phase

A phase of the eukaryotic cell cycle between S phase and M phase in which a cell accumulates the materials necessary for nuclear and cell division.

M phase

the phase of the eukaryotic cell cycle in which nuclear division, either mitosis or meiosis, occurs. It is divided into prophase, prometaphase, metaphase, anaphase, and telophase.

mitosis

a type of nuclear division into two nuclei, during which each daughter cell receives the same complement of chromosomes.

spindle apparatus

during cell division in eukaryotic cells, a structure composed of microtubules that sorts the chromosomes.

microtubule-organizing center (MTOC)

a structure in a eukaryotic cell from which microtubules grow.

centrosome

a cellular structure from which microtubules emanate.

spindle pole

during cell division in eukaryotes, one of two sites in the cell where microtubules originate.

centrioles

a pair of structures within each centrosome of animal cells.

astral microtubules

the microtubules that emanate outward from the centrosome toward the plasma membrane.

polar microtubules

the microtubules that project toward the region where the chromosomes will be found during mitosis; those that overlap with each other play a role in pushing the spindle poles apart.

kinetochore microtubules

the microtubules that are connected to kinetochores on chromosomes.

kinetochore

a protein complex bound to a centromere of a chromosome during meiosis and mitosis.

prophase

the first phase of mitosis. The chromosomes have already replicated and begin to condense. The mitotic spindle apparatus starts to form.

prometaphase

the second phase of mitosis. During this phase, the nuclear membrane vesiculates, and the mitotic spindle is completely formed.

metaphase

the third phase of mitosis. The chromosomes align along the central plane of the spindle apparatus, and the formation of the spindle is completed.

metaphase plate

the plane along which pairs of sister chromatids align during metaphase.

anaphase

the fourth phase of mitosis. As phase proceeds, half of the chromosomes move to one pole, and the other half move to the other pole.

telophase

the fifth stage of mitosis. The chromosomes have reached their respective poles and decondense.

cytokinesis

the division of a single cell into two cells. The two nuclei produced in mitosis are segregated into separate daughter cells during this phase

cleavage furrow

a constriction that causes the division of an animal cell into two cells during cytokinesis.

meiosis

a form of nuclear division in which the sorting process results in the production of haploid cells from a diploid cell.

haploid

refers to a cell that contains half the genetic material found in somatic cells. For a species that is diploid, a —— gamete contains a single set of chromosomes.

synapsis

the event in which homologous chromosomes recognize each other and then align themselves along their entire lengths.

bivalent (tetrad)

a structure in which two pairs of homologous sister chromatids have synapsed (i.e., aligned) with each other.

crossing over/chiasma formation

a physical exchange of pieces between homologous chromosomes that most commonly occurs during prophase of meiosis I.

chiasma

the site where crossing over occurs between two chromosomes. It resembles the Greek letter chi, χ.

gametogenesis

the production of gametes

isogamous

describes a species that produces morphologically similar gametes.

heterogamous

describes a species that produces two morphologically different types of gametes (e.g., sperm and eggs).

spermatogenesis

the production of sperm cells.

oogenesis

the production of egg cells.

gametophyte

the haploid generation of plants.

sporophyte

the diploid generation of plants.

monoecious

in plants, a species in which male and female gametophytes are produced on a single (sporophyte) individual.

dioecious

in plants, a species in which sporophytes are divided into those that produce only male gametophytes and those that produce only female gametophytes.

sex chromosomes

a pair of chromosomes (e.g., X and Y in mammals) that differ between males and females and determine sex in a species.

sex determination

the process that governs the development of male and female individuals.