Biology - Genetics

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

Meiosis

The mature sexual reproductive cell; the egg or the sperm.

Gamete

A pair of matching chromosomes comprises a chromosome from each of the two sets of chromosomes in a diploid organism.

Homologous chromosomes

When chromosomes condense from diffuse, threadlike material to discrete, compact bodies.

Prophase

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

Prometaphase

The stage in the 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.

Metaphase

The stage in cell nuclear division at which the first separation of sister chromatids (or, in the first meiotic division, of paired homologs) occurs.

Anaphase

This is the stage where chromosomes become diffuse, nuclear envelopes re-form, and nucleoli reappear in the daughter nuclei.

Telophase

When homologous chromosomes separate but retain their chromatids.

Meiosis I

The second step in meiosis in which chromatids separate. This step is similar to mitosis.

Meiosis II

The degree to which a genotype is expressed in the phenotype may be affected by the environment.

Expressivity

Condition in which two alleles at a locus produce different phenotypic effects and both effects appear in heterozygotes.

Codominance

Condition in which the heterozygous phenotype is intermediate between the two homozygous phenotypes.

Incomplete dominance

In genetics, alleles separate from each other during meiosis so that each haploid daughter nuclei produced contains one or the other member of the pair found in the diploid parent cell, but never both.

Law of segregation

A mutation that does not change the final gene product.

Silent mutation

A mutation that occurs when one or two bases are inserted or removed from the sequence

Frameshift mutation

Proteins that assemble on a eukaryotic chromosome that allow RNA polymerase II to perform transcription.

Transcription factors

The three nucleotides in transfer RNA pair with a complementary triplet (a codon) in messenger RNA.

Anticodon

Three nucleotides in messenger RNA direct the placement of a particular amino acid into a polypeptide chain.

Codon

A DNA sequence to which RNA polymerase binds to initiate transcription.

Promoter

The synthesis of a protein (polypeptide). Takes place on ribosomes, using the information encoded in messenger RNA.

Translation

The synthesis of RNA using one strand of DNA as a template.

Transcription

Strand of nucleic acid, usually RNA, that is the necessary starting material for the synthesis of a new DNA strand, which is synthesized from the 3' end of the primer.

Primer

In DNA replication, the daughter strand is synthesized in discontinuous stretches.

Leading strand

In DNA replication, the daughter strand is synthesized in discontinuous stretches.

Lagging strand