Meiosis Flashcards
What is meiosis?
The process by which diploid cells become haploid cells. It only occurs in the production of gametes in sexually reproducing organisms and takes place in the ovaries and testes.
What happens during Meiosis?
Meiosis is a reduction division during which a diploid cell divides into four daughter cells each containing half the number of chromosomes of the original cell.
Why is Meiosis often called reduction division?
Reduction division is a special type of division during which the chromosome number is reduced from diploid (46 chromosomes) to haploid (23 chromosomes).
What the stages of Meiosis?
Prophase I Metaphase I Anaphase I Telophase I Cytokinesis Prophase II Metaphase II Anaphase II Telophase II Cytokinesis
Prophase I
The chromosomes condense and are visible. Crossing over can occur here if a chromosomes homologous pair is found. The nucleus disassembles.
Metaphase I
Chromosomes line up in the middles in homologous pairs.
Anaphase I
Homologous chromosomes are pulled away from each other in opposite directions via spindle fibres attached to the centromere.
Telophase I
Chromosomes are at opposite poles, new nuclei form in the 2 daughter cells.
Cytokinesis
The cell membrane constricts in the centre of the cell, forming a narrow area of cytoplasm, which consequently breaks forming two cells.
Prophase II
Chromosomes in two cells are visible, crossing over doesn’t occur.
Metaphase II
Chromosomes line up in the middle in single file line (not with homologous chromosomes).
Anaphase II
Chromatids are pulled away.
Telophase II
Chromosomes are at opposite poles, new nuclei will form in four daughter cells each with 23 chromosomes.
Crossing Over
Homologous chromosomes pair up as meiosis begins. Genetic material is exchanged between chromatids. Making a new combination of genetic material. Crossing over results in increased genetic variation.
Homologous in chromosomes
Having the same or allelic genes with genetic loci usually arranged in the same order
