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meiosis, mitosis

heredity

The transmission of traits from one generation to the next.

variation

Differences between members of the same species.

genetics

The scientific study of heredity and hereditary variation.

gene

A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).

asexual reproduction

The generation of offspring from a single parent that occurs without the fusion of gametes (by budding, division of a single cell, or division of the entire organism into two or more parts). In most cases, the offspring are genetically identical to the parent.

clone

(1) A lineage of genetically identical individuals or cells. (2) In popular usage, a single individual organism that is genetically identical to another individual. (3) As a verb, to make one or more genetic replicas of an individual or cell. See also gene cloning.

somatic cells

any cell in multicellular organism except an egg or sperm

syngamy

the union of gametes in fertilization

karyotype

A display of the chromosome pairs of a cell arranged by size and shape.

autosomes

chromosomes that are not directly involved in determining the sex of an individual

haploid cells

A cell containing only one set of chromosomes (n).

diploid cells

A cell containing two sets of chromosomes (2n), one set inherited from each parent.

homologous chromosomes

A pair of chromosomes of the same length, centromere position, and staining pattern that possess genes for the same characters at corresponding loci. One homologous chromosome is inherited from the organism's father, the other from the mother. Also called homologs, or a homologous pair.

zygote

The diploid product of the union of haploid gametes in conception; a fertilized egg

alternation of generations

A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae.

synapsis

The pairing and physical connection of replicated homologous chromosomes during prophase I of meiosis.

tetrad

A four-part structure that forms during the prophase of meiosis and consists of two homologous chromosomes, each composed of two sister chromatids.

chiasma

The X-shaped, microscopically visible region where homologous nonsister chromatids have exchanged genetic material through crossing over during meiosis, the two homologs remaining associated due to sister chromatid cohesion.

crossing over

The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis.

random segregation

During meiosis the two separated partners of a chromosome pair are distributed randomly to the reproductive cells gametes, each gamete having an equal chance of receiving either chromosome

Prophase 1

replicated homologous chromosomes pair and exchange segments

Metaphase 1

Chromosomes line up by homologous pairs

Anaphase 1

Each pair of homologous chromosomes separates

Telophase 1

2 haploid cells form; each chromosome still consists of 2 sister chromatids

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