Meiosis Biology

Meiosis

A type of cell division that occurs only in sexual reproduction, producing gametes with half the chromosome number of the parent cell.

Homologous Chromosomes

Pairs of chromosomes, with one from each parent, that carry different versions of the same genes in the same locations.

Karyotype

An ordered display of magnified images of an individual's chromosomes arranged in pairs, with the first 22 pairs being autosomes and the last 2 being sex chromosomes.

Sex Chromosomes

One pair of chromosomes that determines the gender of an individual, with the other 22 pairs being autosomes.

Haploid

Having one set of chromosomes per cell, such as in gametes.

Diploid

Having two sets of chromosomes per cell, with one set from each parent.

Gametes

Sex cells produced by meiosis in the ovaries and testes, with half the chromosome number of the parent cell.

Interphase

The phase before meiosis I where DNA replication occurs, similar to the interphase in mitosis.

Meiosis I

The first stage of meiosis involving the separation of homologous chromosomes, chromosome duplication, and the formation of two haploid cells.

Meiosis II

The second stage of meiosis immediately following Meiosis I, involving the separation of sister chromatids to produce four haploid daughter cells.

Prophase I

The initial phase of Meiosis I where chromosomes condense, nuclear membrane breaks down, and crossing over occurs.

Metaphase I

The phase of Meiosis I where pairs of chromosomes line up randomly.

Anaphase I

The phase of Meiosis I where homologous chromosomes separate.

Telophase I

The phase of Meiosis I where new nuclear membranes form.

Cytokinesis

The division of the cytoplasm to form two cells, occurring at the end of Meiosis I.

Metaphase II

The phase of Meiosis II where chromosomes line up at the equator.

Anaphase II

The phase of Meiosis II where centromeres divide and sister chromatids separate.

Telophase II

The phase of Meiosis II where daughter chromosomes migrate to opposite poles.

Prophase II

Nuclear membranes break down.

Meiosis Increases Genetic Variation

Meiosis produces haploid cells not identical to parent cell, with genetic variation from crossing over and independent assortment of homologues.

Crossing Over

Exchange of homologous parts between non-sister chromatids, leading to genetic variation.

Independent Assortment

Random separation of homologous chromosomes in meiosis I, contributing to genetic variability.

Chiasma

The site where crossing over occurs, visually revealed as chiasmata.

Genetic Recombination

Production of new gene combinations due to crossing over.

Parental v. Recombinant

Comparison between offspring with genetic material from parents and those with new gene combinations.

Sister chromatids

Identical copies of a chromosome connected at the centromere.

Non-Sister chromatids

Chromatids from different chromosomes or homologous chromosomes.

Chromosomes line up independently during metaphase I

Process where chromosomes arrange independently, contributing to genetic diversity.

Meiosis I/Cytokinesis I

At the end of meiosis I, there are 2 cells, each with half the number of chromosomes, entering the next stage.

Meiosis II/Cytokinesis II

At the end of meiosis II, there are 4 cells, each with a haploid set of chromosomes, formed after the second round of division.

Comparison of Mitosis & Meiosis

Contrast between the processes of cell division in terms of DNA replication, number of divisions, daughter cells produced, ploidy, and genetic variability.

Mitosis

Cell division in somatic cells resulting in two diploid, genetically identical daughter cells.

Human Life Cycle

Description of diploid and haploid states in the human life cycle, emphasizing chromosome sets in cells and reproductive cells.

Somatic Cells

Our body cells that are diploid.

Fertilization

Combining of egg and sperm to form a diploid zygote.

Zygote

Result of fertilization, which grows into an embryo and then a baby.

Prophase

First stage of cell division where chromosomes condense and spindle fibers form.

Metaphase

Stage where chromosomes line up in the middle of the cell.

Anaphase

Stage where chromosomes are pulled apart to opposite sides of the cell.

Telophase

Final stage of cell division where chromosomes arrive at opposite poles.

Synapsis

Pairing of homologous chromosomes during meiosis.

Crossing over

Exchange of DNA between homologous chromosomes during meiosis.

Genetic Variation

Result of sexual reproduction mixing up genes through processes like crossing over and random alignment.

Genes

Units of heredity that are passed from parents to offspring.

Chromatin

Loose form of DNA in the nucleus.

Daughter Cells

Cells produced at the end of cell division.