Meiosis Flashcards
_______ is the type of cell division that produces sex cells / gametes (eggs and sperm.) it occurs in special sex organs. During _______, chromosomes replicate once, but divide twice. As a result _______ produces four haploid gametes from a single cell. For this reason _______is sometimes called a reduction division.
Meiosis
Humans have 46 chromosomes - 23 homologous pairs (diploid) Because of meiosis, gametes are produced with half this number of chromosomes - 23 individual chromosomes (haploid). As a result, when the genetic material of egg and sperm combine, the resulting zygote will have the normal number of 46 chromosomes (23 homologous pairs). Consequently, meiosis ensures that the number of chromosomes in a particular species will remain constant upon fertilization, generation after generation. If diploid gametes were produced, the number of chromosomes in each cell would double every generation.
What is the significance of meiosis?
22 pairs of body chromosomes, don’t directly determine gender.
Autosomes
One pair of these determines gender (XX or XY)
Sex Chromosomes
Sex cells, eggs and sperm.
Gametes
Fusion of the genetic material of male and female gametes.
Fertilization
Single cell forward from fertilization.
Zygote
(2n) Those cells that have all the homologous chromosomes that are characteristic of a species. Characteristics of somatic cells/body cells
Diploid
The same as __________ of mitosis. I.e.. This is a period of growth when the cell undergoes normal day to day activities including protein synthesis. Genetic material exists as long thin twisted threads called chromatin. Chromatin replicates. The Nuclear membrane and nucleolus are present and visible. Centrioles replicate to form two pairs
Interphase (Meiosis)
Pairs of centrioles move to opposite ends of the cell. Nuclear membrane and nucleolus disintegrate.(disappear) Sister chromatids form from the replicated chromatin as it condenses. Sister chromatids are joined at the centromere. Homologous chromosomes pair up (synapsis) to form a tetrad. Genetic material may be exchanged between homologous chromosomes. This exchange of genetic material increases variation and is called crossing over. Crossing over increases genetic variation. Mitotic spindle forms
Prophase 1
Tetrads line up at the equator of the cell, one homologous chromosome on each side.
Metaphase 1
Homologous chromosomes are pulled apart by the mitotic spindle. (Disjunction). The cluster of chromosomes around each end is now haploid but still has 2 identical sister chromatids.
Anaphase 1
Cell divides into two smaller haploid cells by cytokinesis. Nuclear membrane reforms around each group of chromosomes
Telophase 1
The chromatin condenses in each of the two cells to form the sister chromatids. These move toward the middle of the cell.
Prophase 2
Sister chromatids line up along the equator of the cells, one on each side.
Metaphase 2
Sister chromatids are pulled to opposite ends of the cell by the mitotic spindle. Each individual chromatid is now called a chromosome.
Anaphase 2
Both cells divide by cytokinesis to form 4 haploid cells. Nuclear membrane reforms around each set of chromosomes
Telophase 2
Chromosomes - during metaphase 1 the homologous chromosomes line up randomly. Each member of the pair could be on any side with regard to an adjacent pair. Because each pair is not identical we can get different arrangements being pulled to opposite sides during anaphase 1. This creates different genetic combinations in egg and sperm
Independent Assortment of Chromosomes
