BIOL B110: Meiosis

Locus

Gene's specific location along length of chromosome

Genome

Genes and other DNA that make up chromosomes inherited from parents

Karyotype

Ordered display of 23 chromosome pairs of 1 cell in mitosis, starting with longest chromosomes

Homologous chromosomes (homologs)

Individual chromosomes that were inherited from each parent

Sister chromatids

2 copies of 1 chromosome that are closely associated all along their lengths

Sex chromosomes

X and Y chromosomes, determine biological sex

Autosomes

Chromosomes other than sex chromosomes

Diploid cell

Cell with 2 chromosome sets

Haploid cell

Cell with 1 chromosome set

Meiosis

Type of cell division that results in gamete formation

Meiosis I

Separates homologous chromosomes

Prophase I

Duplicated homologous chromosomes pair up and exchange segments

Crossing over

DNA molecule of nonsister chromatids broken and rejoined to each other

Chiasmata

X-shaped regions on each homologous pair where crossovers have occurred

Metaphase I

Chromosomes line up by homologous pairs

Anaphase I

2 homologous chromosomes of each pair separate

Telophase I and Cytokinesis

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

Meiosis II

Sister chromatids separate, four haploid daughter cells result, containing unduplicated chromosomes

Prophase II

Chromosomes move towards metaphase II plate

Metaphase II

Chromosomes that aren't genetically identical are positioned at metaphase plate

Anaphase II

Sister chromatids separate

Telophase II and Cytokinesis

4 genetically distinct haploid cells form

Synaptonemal complex

Zipper-like structure that holds 1 homolog tightly to the other

Synapsis

Side-by-side pairing of homologous maternal and paternal chromosomes at the start of meiosis

Events unique to meiosis I

- Synapsis and crossing over
- Alignment of homologous pairs at metaphase plate
- Separation of homologs

DNA replication in mitosis vs. meiosis

- Mitosis: occurs during interphase before mitosis begins
- Meiosis: occurs during interphase before meiosis I but not meiosis II

Number of divisions in mitosis vs. meiosis

- Mitosis: 1, including prophase, prometaphase, metaphase, anaphase, telophase
- Meiosis: 2, each including prophase, metaphase, anaphase, and telophase

Synapsis of homologous chromosomes in mitosis vs. meiosis

- Mitosis: doesn't occur
- Meiosis: occurs during prophase I along with crossing over between nonsister chromatids, resulting chiasmata hold pairs together due to sister chromatid cohesion

Number of daughter cells and genetic composition in mitosis vs. meiosis

- Mitosis: 2, same chromosome number, genetically identical
- Meiosis: 4, haploid, genetically different