Science 9 Biology

science

Mitosis

cell division in which the nucleus divides into nuclei containing the same number of chromosomes

Meiosis

the process by which the number of chromosomes is reduced by half to form sex cells

Haploid

an organism or cell having only one complete set of chromosomes

Diploid

an organism or cell having two sets of chromosomes or twice the haploid number

Chromosomes

threadlike structures made of DNA molecules that contain the genes

Chromatid

Each half of the chromosome

Centromere

Area where the chromatids of a chromosome are attached

Centrioles

organelle involved in the development of spindle fibers in cell division.

spindle fibers

help pull apart the cell during replication and are made up of micrtubules

Anaphase

Phase of mitosis in which the chromosomes separate and move to opposite ends of the cell

Metaphase

Chromosomes line up in the middle of the cell

Interphase

Cell grows, performs its normal functions, and prepares for division; consists of G1, S, and G2 phases

Prophase

Chromosomes become visable, nuclear envelop dissolves, spindle forms

Telophase

phase of mitosis in which the distinct individual chromosomes begin to spread out into a tangle of chromatin

Cytokinesis

Division of the cytoplasm during cell division

crossing over

Process in which homologous chromosomes exchange portions of their chromatids during meiosis.

homologous chromosomes

Pair of chromosomes that are the same size, same appearance and same genes.

Telophase II and Cytokinesis

Forms the product of 4 daughter haploid cells.

Telophase I

Cytokinesis occurs, the result are two haploid daughter cells

Nucleus

A part of the cell containing DNA and RNA and responsible for growth and reproduction

nuclear envelope

A double membrane that surrounds the nucleus in the cell

Fertilization

Process in sexual reproduction in which male and female reproductive cells join to form a new cell

Gametes

a mature haploid male or female germ cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote.

Zygote

a diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum.

asexual reproduction

Process by which a single parent reproduces by itself

Budding

Asexual reproduction in which a part of the parent organism pinches off and forms a new organism

vegetative reproduction

a form of asexual reproduction in which offspring grow from a part of a parent plant

Fragmentation

A means of asexual reproduction whereby a single parent breaks into parts that regenerate into whole new individuals.

binary fission

A form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size

spore formation

an asexual reproductive process in which an organism forms a special cell called a spore.

sexual reproduction

A reproductive process that involves two parents that combine their genetic material to produce a new organism, which differs from both parents

internal fertilization

Process in which eggs are fertilized inside the female's body

external fertilization

The process by which the female lays eggs and the male fertilizes them once they are outside of the female

theraputic cloning

used to produce human tissues that can be begin with embryotic or adult stem cells

reproductive cloning

Using a somatic cell from a multicellular organism to make one or more genetically identical individuals.

somatic cells

body cells

DNA

A complex molecule containing the genetic information that makes up the chromosomes.

independent assortment

Part of metaphase 1 and 2 of meiosis when the chromosomes line up in a random order. This increases genetic variation.

G1 Phase

The first growth phase of interphase where the cell increases in size, produces proteins, and carries out normal cell functions.

S Phase

The synthesis phase of interphase where DNA replication occurs, resulting in chromosomes with two sister chromatids.

G2 Phase

The second growth phase of interphase where the cell continues to grow and prepares for cell division.

Sister Chromatids

Identical copies of a chromosome that are joined together at the centromere following DNA replication.

Reduction Division

The first division of meiosis (meiosis I) where homologous chromosomes separate, reducing the chromosome number from diploid to haploid.

Equational Division

The second division of meiosis (meiosis II) where sister chromatids separate, similar to mitosis.

Synapsis

The pairing of homologous chromosomes during prophase I of meiosis.

Tetrad

A structure formed when homologous chromosomes pair up during prophase I of meiosis, consisting of four chromatids.

Chiasmata

The X-shaped structures visible during prophase I of meiosis where crossing over occurs between non-sister chromatids.

Genetic Recombination

The production of new combinations of alleles as a result of crossing over during meiosis.

Ploidy

The number of complete sets of chromosomes in a cell.

Monoploid

A cell containing only one set of chromosomes, regardless of the typical number for the species.

Prophase I

The first phase of meiosis I where homologous chromosomes pair up and crossing over occurs.

Metaphase I

The phase of meiosis I where homologous chromosome pairs line up along the metaphase plate.

Anaphase I

The phase of meiosis I where homologous chromosomes separate and move to opposite poles.

Prophase II

The first phase of meiosis II where the nuclear envelope breaks down and spindles form in each daughter cell.

Metaphase II

The phase of meiosis II where chromosomes align at the metaphase plate in each daughter cell.

Anaphase II

The phase of meiosis II where sister chromatids separate and move to opposite poles.

Alternation of Generations

A life cycle in which there is both a multicellular diploid form and a multicellular haploid form.

Gametophyte

The haploid, gamete-producing phase in plants and some algae.

Sporophyte

The diploid, spore-producing phase in plants and some algae.

Karyotype

The complete set of chromosomes of an organism, often displayed as an organized visual profile.

Nondisjunction

An error in cell division where chromosomes fail to separate properly, leading to abnormal chromosome numbers in daughter cells.

Cell Cycle

The sequence of growth and division that cells undergo, consisting of interphase (G1, S, G2) and cell division (mitosis/meiosis and cytokinesis).

Autosome

Any chromosome that is not a sex chromosome.

Sex Chromosomes

The pair of chromosomes responsible for determining the sex of an organism (X and Y in mammals).

Genetic Diversity

The variety of genes within a species, enhanced by sexual reproduction through crossing over and independent assortment.

Cleavage

The rapid series of mitotic divisions that occurs after fertilization in animal development.

Blastula

An early stage of embryonic development consisting of a hollow ball of cells.

Gastrula

The embryonic stage that follows the blastula, characterized by the formation of the three primary germ layers.