Meiosis is the nuclear division that makes sexual reproduction possible by reducing the number of chromosome sets. This lesson introduces chromosome sets, explains how meiosis differs from mitosis, and covers the preparation for meiosis and the chromosome pairing and crossing over that begin in prophase I.
The number of chromosome sets in a cell is its ploidy level. A haploid cell has one set of chromosomes; a diploid cell has two. In most animals and plants, nonreproductive body cells, or somatic cells, are diploid.
All flashcards
What is ploidy?
Ploidy is the number of chromosome sets in a cell. Haploid cells have one set, while diploid cells have two.
What are homologous chromosomes?
They are a matched pair of chromosomes with genes for the same traits at corresponding locations. One is generally inherited from each parent.
What happens during interphase before meiosis?
The cell grows in G₁, replicates chromosome DNA in S phase, and makes final preparations in G₂. Each replicated chromosome has two sister chromatids.
What is synapsis?
Synapsis is the close pairing of homologous chromosomes during prophase I, allowing corresponding genes to align.
What are crossing over and chiasmata?
Crossing over is the exchange of DNA between non-sister chromatids of homologous chromosomes. Chiasmata are the visible points where the homologs remain connected after exchange.
Quiz questions
What does the ploidy level of a cell describe?Answer: The number of chromosome sets in the cell.
Why must meiosis reduce chromosome sets before fertilization?Answer: So fusion of two gametes restores the diploid number instead of increasing it each generation.
What happens to a chromosome during the S phase before meiosis?Answer: Its DNA is copied, producing two sister chromatids joined at the centromere.
Which event describes synapsis?Answer: Homologous chromosomes pair closely and align corresponding genes.
How can crossing over increase genetic variation?Answer: It exchanges DNA between non-sister chromatids, creating new combinations of parental DNA.
Based on Concepts of Biology by Samantha Fowler, Rebecca Roush, James Wise (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.