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Ch. 11 The Science of Biology, Sadava *All definitions from the glossary


The duplication of genetic material


In genetics, the separation of alleles, or of homologous chromosomes, from each other during meiosis so that each of the haploid daughter nuclei produced contains one or the other member of the pair found in the diploid parent cell, but never both. This principal was founded by Mendel as his first law.


The division of the cytoplasm of a dividing cell.

Binary Fission

Reproduction of a prokaryote by division of a cell into two comparable progeny cells.


In eukaryotes, a structure composed of DNA and proteins that bears part of the genetic information of the cell.

Sister Chromatid

Each of a pair of newly replicated chromatids.


Nuclear division in eukaryotes leading to the formation of two daughter nuclei, each with a chromosome complement identical to that of the original nucleus.


Division of a diploid nucleus to produce four haploid daughter cells. The process consists of two successive nuclear divisions with only one cycle of chromosome replication. In meiosis I, homologous chromosomes separate but retain their chromatids. The second division meiosis II, is similar to mitosis in which chromatids separate.


The period between successive nuclear divisions during which the chromosomes diffuse and the nuclear envelope is intact. During interphase the cell is most active in transcribing and translating genetic information.

S Phase

The stage of interphase during which DNA is replicated.


The gap between the end of mitosis and the onset of the S phase.


The gap between the S phase and the onset of mitosis.

M Phase

The portion of the cell cycle in which mitosis takes place.

Restriction Point

The specific time G1 of the cell cycle at which the cell becomes committed to undergo the rest of the cell cycle.

Cyclin- Dependent Kinases

A protein kinase whose target proteins are involved in transitions in the cell cycle and which is active only when complexed with additional protein subunits , called cyclins.

Growth Factor

A chemical signal that stimulates cells to divide.


The nucleic acid-protein complex that makes up eukaryotic chromosomes.


The region where sister chromatids join.


Any one of a group of proteins forming the core of a nucleosome, the structural unit of a eukaryotic chromosome.


A portion of a eukaryotic chromosome, consisting of part of the DNA molecule wrapped around a group of histone molecules, and held together by another type of histone molecule.


The first stage of nuclear division, during which chromosomes condense from diffuse, threadlike material to discrete, compact bodies.


Array of microtubules emanating from both poles of a dividing cell during mitosis and playing a role in the movement of chromosomes at nuclear division.


The phase of nuclear division that begins with the disintegration of the nuclear envelope.


The stage in nuclear division at which the centromeres of the highly supercoiled chromosomes are all lying on a plane perpendicular to a line connecting the division poles.


The stage in cell nuclear division at which the first separation of sister chromatids occurs.

Daughter Chromosomes

During mitosis, the separated chromatids from the beginning of anaphase onward.


The final phase of mitosis or meiosis during which chromosomes became diffuse, nuclear envelopes reform, and nucleoli begin to reappear in the daughter nuclei.

Asexual reproduction

Reproduction without sex.

Sexual reproduction

Reproduction involving the union of gametes.


In cytogenetics, one pair of chromosomes having the same overall genetic decomposition and sequence. In diploid organisms, each chromosome inherited from one parent is matched by an identical chromosome from the other parent.


Having a chromosome complement consisting of just one copy of each chromosome.


Union of gametes.


Having a chromosome complement consisting of two copies of each chromosome.

Alteration of generations

The succession of multicellular haploid and diploid phases in some sexually reproducing organisms, notably plants.


The number forms, and types of chromosomes in a cell.


The highly specific parallel alignment of homologous chromosomes during the first division of meiosis.


During prophase I of meiosis, the association of a pair of homologous chromosomes or four chromatid.


An X-shaped connection between paired homologous in prophase I of meiosis. A chiasma is the visible manifestation of crossing over between homologous chromosomes.

Crossing over

The reciprocal exchange of corresponding segments between two homologous chromatids.

Independent assortment

During meiosis, the random separation of genes carried on non-homologous chromosomes into gametes so that inheritance of these genes is random. This principal was articulated by Mendel as his second law.


Failure of sister chromosomes to separate in meiosis II or mitosis, or failure of homologous chromosomes to separate in meiosis I.


Premature cell death caused by external agents such as toxins.


A condition in which one or more chromosomes or pieces of chromosomes are either lacking in or present in excess.


A series of genetically programmed events leading to cell death.

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