Biology 30 - Chapter 16

cell cycle

a continuous sequence of cell growth and division; the life cycle of a cell

somatic cell

any of the cells of a multicellular organism except those that form gametes

parent cell

original cell that divides to produce two new daughter cells during cell division

daughter cell

any one of two cells produced from the division of a parent cell

DNA

a double-stranded nucleic acid molecule that governs the processes of heredity in the cells of organisms; composed of nucleotides containing a phosphate group, a nitrogenous base (adenine, guanine, cytosine, or thymine), and deoxyribose

Chromosome

a length of DNA and its associated proteins

Histones

protein found in chromosomes; acts as scaffold around which DNA winds, enabling it to fit within the small space of the nucleus

Chromatin

long fibres that form chromosomes and contain DNA, a small amount of RNA, and various proteins; non-condensed form of genetic material that predominates for most of the cell cycle

Centromere

the point at which two sister chromatids of a chromosome are joined and to which the spindle fibres are attached during mitosis

homologous chromosomes

chromosome that contains the same gene sequence as another, but that may not be made up of the same alleles; human somatic cells have 22 pairs of these, known as autosomes, and females also have a homologous pair of X sex chromosomes; males have an X and a Y sex chromosome which are not homologous

Autosomes

chromosome other than a sex chromosome; human somatic cells have 22 pairs of these

sex chromosomes

X or Y chromosome that carries the genes involved in determining the genetic sex of an individual

Genes

the basic unit of heredity; a specific sequence of DNA that encodes a protein, tRNA, rRNA molecule, or regulates the transcription of such a sequence; governs the expression of a particular trait and can be passed to an offspring

Locus

specific location on a chromosome

Allele

different form of the same gene occurring on homologous chromosomes

Diploid

describing a cell that contains two pairs of every chromosome, designated as 2n; e.g., somatic cells

Haploid

describing a cell containing half the number of chromosomes (n) that the diploid (2n) parent cell contains; condition occurring in gametes, either egg (ovum) or sperm

Gamete

male or female haploid reproductive cell; e.g., egg (ovum) and sperm

Polyploid

describing a cell which contains sets of more than two homologous chromosome

Karyotype

the particular set of chromosomes that an individual possesses

Interphase

growth stage of a somatic cell; there are 3 phases

G1 phase

the first part of interphase, a somatic cell’s growth stage, during which cells carry out rapid growth and metabolic activity; also known as Growth 1 or Gap 1

S phase

the middle part of interphase, a somatic cell’s growth stage, during which the cell’s DNA is replicated

sister chromatids

two chromatids in a chromosome that are genetically identical and are held together by a centromere

G2 phase

the last part of interphase, a somatic cell’s growth stage, during which the cell rebuilds its reserves of energy and manufactures proteins and other molecules to prepare for division; also known as Growth 2 or Gap 2

Mitosis

one of the two main processes in cell division

Cytokinesis

one of the two main processes in cell division; consists of separation of cytoplasm and organelles and the formation of two daughter cells

Prophase

the first of the four phases in cell division (mitosis), when chromatin condenses and can be seen as tightly packed chromosomes; the nuclear membrane breaks down, centrioles move to opposite poles of the cell, and the spindle apparatus forms

Centriole

one of a pair of cylindrical organelles that moves to opposite poles of the cell during prophase of mitosis; provides an attachment for the spindle apparatus

spindle apparatus

assembly that carries out the separation of chromosomes during cell division (mitosis); composed of spindle fibres and assembled during prophase

Metaphase

the second stage of cell division (mitosis) during which chromosomes line up at the cell’s equator in preparation for separation

Anaphase

a late stage of cell division (mitosis) during which the centromere splits apart and chromosomes move to opposite poles of the cell; by the end of the phase, one complete diploid set of chromosomes has been gathered at each pole

Telophase

the final stage of cell division (mitosis) in which a nucleolus forms around chromosomes at opposite ends of the dividing parent cell; this stage is followed by cytokinesis to form two daughter cells

cell plate

structure across a dividing plant cell that signals the location of new plasma membranes and cell walls

Cancer

group of diseases associated with uncontrolled, rapid cell division

Meiosis

the cellular process that produces haploid gametes from diploid cells in the ovaries and testes

reduction division

one of the outcomes of meiosis

Recombination

one of the outcomes of meiosis which is cell division that produces daughter cells with different combinations of genes than the parent cells; gives rise to offspring that are genetically distinct from one another and from their parents

meiosis I

the first of two sequences in meiotic cell division in which the chromosomes are reduced from diploid to haploid (2n to n)

meiosis II

the second of two sequences in meiotic cell division in which each of the haploid cells created during meiosis I undergoes mitosis (without an interphase)

germ cells

gamete-producing cell in the male and female gonads

Synapsis

aligning of homologous chromosomes side-by-side during prophase I in meiosis

Tetrad

a homologous pair formed during prophase I of meiosis, so named because it contains four chromatids

non-sister chromatids

in a tetrad, those chromatids that do not belong to the same chromosome; undergo crossing over during prophase I of meiosis

crossing over

the process by which non-sister chromatids exchange genes during prophase I of meiosis, allowing for the recombination of genes

Nondisjunction

failure of homologous chromosomes pairs or sister chromatids to separate during meiosis I and meiosis II, respectively

Spermatogenesis

the process of male gamete (sperm) production in animals

Oogenesis

the process of female gamete (ova or egg) production in animals

Spermatogonium

the diploid germ cell from which sperm are produced in the testes

primary spermatocyte

one of two daughter cells formed by division of the spermatogonia; the other daughter cell replenishes the spermatogonia population

secondary spermatocyte

each of two cells produced as a result of a primary spermatocyte undergoing meiosis I

Spermatids

each of four haploid cells that result when a secondary spermatocyte undergoes meiosis II; each spermatid differentiates into a sperm cell

Oogonium

the diploid germ cell from which eggs are produced in the ovaries

primary oocyte

each of two cells formed when an oogonium undergoes mitosis

secondary oocyte

cell that receives the larger portion of cytoplasm when a primary oocyte undergoes asymmetrical cytokinesis during meiosis I; becomes the egg

first polar body

cell that receives the smaller portion of cytoplasm when a primary oocyte undergoes asymmetrical cytokinesis during meiosis I; is not functional and soon degenerates; compare secondary oocyte

second polar body

one of a pair of cells that results when when a secondary oocyte undergoes asymmetrical cytokinesis during meiosis II; is not a viable gamete; also used to refer to the products of a second division that may occur in the first polar body

asexual reproduction

reproduction that requires only one parent and does not involve gametes; produces genetically identical offspring

sexual reproduction

reproduction involving meiosis, gamete formation, and fertilization; produces genetically distinct offspring

binary fission

asexual reproductive process of cell division in bacteria; produces genetically identical populations

Conjugation

in micro-organisms, a process of reproduction that involves the transfer of genetic material from one cell to another by cell-to-cell contact through a bridging structure; creates cells with new genetic combinations

Pilus

extensions of a bacterial cell enabling it to transfer genetic materials from one individual to another through the process of conjugation

Budding

asexual form of reproduction whereby a new organism develops as an outgrowth of the body of the parent

vegetative reproduction

a form of asexual reproduction in which a new plant grows from a modified stem

Fragmentation

form of asexual reproduction in which a new organism is created from a fragment (portion) of a parent organism

Parthenogenesis

form of asexual reproduction in which an unfertilized egg develops into an adult

Spore

reproductive cell capable of developing into a new organism without fusion with another cell, in contrast to a gamete; contains genetic material and cytoplasm surrounded by a protective sheath or wall

alternation of generations

term describing the life cycle of a plant that alternates between a diploid sporophyte generation and a haploid gametophyte generation

Sporophyte

diploid generation of a plant that produces haploid spores (through the process of meiosis) that develop without fertilization into a gametophyte; also see alternation of generations

Gametophyte

haploid generation of a plant; produces male and female gametes that fuse at fertilization to form a diploid sporophyte; also see alternation of generations