Comprehensive Guide to Meiosis, Genetics, and Cell Division

Meiotic division

Conversion of diploid (2N) to haploid (N) gametes.

Heredity

Transmission of hereditary units (genes) from one generation to next.

Variation

Inherited differences among individuals of the same species.

Chromosomes

Functional units of heredity located in the eukaryotic nucleus, comprised of strands of DNA.

Gene

A sequence (series) of nucleotides that may include hundreds of thousands of nucleotides and associated proteins.

Locus

Exact position of the gene along the strand of DNA.

Asexual Reproduction

Reproduction involving one parent, resulting in genetically identical offspring (except mutations).

Sexual Reproduction

Reproduction involving two parents, resulting in large genetic variability among offspring.

Genetic Variation

Caused during sexual reproduction by meiosis, which is the specific division resulting in haploid gametes.

Diploid (2N)

Cells that contain two complete sets of chromosomes, one from each parent.

Haploid (N)

Cells that contain one complete set of chromosomes.

Fertilization

Restores diploid (2N) number of chromosomes by fusing haploid (1N) gametes to form a diploid (2N) zygote.

Zygote

The diploid cell formed by the fusion of haploid gametes during fertilization.

Mitosis

The process by which a cell divides to produce genetically identical diploid cells.

Cytokinesis

The process that follows mitosis, resulting in the division of the cytoplasm and formation of two daughter cells.

Homologous DNA

Molecules of DNA that are comparable in size and form, containing genes for the same trait at the same locus.

Maternal Origin

Refers to one member of a homologous chromosome pair that is inherited from the mother.

Paternal Origin

Refers to one member of a homologous chromosome pair that is inherited from the father.

Centromere

The region of a chromosome where two sister chromatids are joined.

Color-stain banding pattern

A characteristic pattern observed in chromosomes that helps identify homologous pairs.

Interphase

Exact same conditions as the starting point of Mitosis.

Nuclear membrane

Complete during Interphase.

DNA

In chromatin form during Interphase.

Centrioles

Begin to appear in cytoplasm during Interphase.

Meiosis I

The first division in meiosis, consisting of Prophase I, Metaphase I, Anaphase I, and Telophase I.

Prophase I

Nuclear membrane begins to dissociate; centrioles migrate toward poles; DNA undergoes duplication and condensation into chromatids.

Synapsis

Opposite homologues, in chromatids form, closely wound together, each unit known as a tetrad.

Crossing over

Bonds among nucleotides de-stabilize, allowing tips of chromatids to break off and exchange positions.

Metaphase I

Nuclear membrane is fully dispersed; DNA is in chromatid form; tetrads are suspended by spindle fibers.

Anaphase I

Contraction of spindle fibers separates homologues; synapsis is lost.

Telophase I

Cytokinesis occurs; nuclear membranes re-form in 2 new cells.

End results of Meiosis I

Homologues are separated; cells are haploid.

Meiosis II

There is no interphase between Meiosis I and Meiosis II; it is a mitotic-type of division.

Prophase II

Cleavage furrow pinches off, producing 2 new cells containing chromatids that have undergone crossing over.

Metaphase II

Chromatids migrate to the equatorial plane.

Anaphase II

Contraction of spindle fibers separates chromatids; first appearance of chromosomes.

Telophase II

Cleavage furrow separates development of 2 new cells; each new cell is now haploid.

Unique events in meiosis

Include synapsis, crossing over, and random separation of homologues during Anaphase I.

Possible orientations

223 possible orientations during random separation of homologues.

Meiotic events contributing to variation

Crossing over and random separation of homologues at Anaphase I.

Comparison of Mitosis & Meiosis

Mitosis is for growth and regeneration; Meiosis is for reduction division.

Resulting Cells in Mitosis

2 genetically identical 2N somatic cells.

Resulting Cells in Meiosis

4 haploid gametes.

Type of Cells in Mitosis

Somatic daughter cells.

Type of Cells in Meiosis

Germ cells or gametes.