Meiosis
Mar 27, 2015
Meiosis
• Haploid (n)-- one set of chromosomes
• Diploid (2n)-- two sets of chromosomes
• Most plant and animal and adult cells are diploid (2n)
• Eggs and sperm are haploid (n)
• Meiosis is a process to convert a diploid cell to a haploid gamete, and cause a change in the genetic information to increase diversity in the offspring.
• Interphase
• During this stage, each individual chromosome replicates,
•
Prophase 1
• Each chromosome then actively seeks out its homologous chromosome, as shown in the graphical representation. After the homologous chromosomes pair, the structure is referred to as a tetrad (four chromatids)
Metaphase 1
• At metaphase, each chromosome has reached its maximum density. The homologous pairs allign at the center of the cell.
• Small fibers attach to the centromere.
Metaphase I
Metaphase I
Anaphase 1
• Anaphase I pulls apart the tetrad, separating each homologous chromosome.
Anaphase 1
Telophase 1
• two nuclear envelopes begin to surround the separate chromosomes and two separate cells form
Telophase
Prophase2
• During Prophase II, each dyad (1/2 a tetrad) is composed of a pair of sister chromatids and they are connected by a centromere
• Begins to move toward center of cell
Prophase2
Metaphase2
• Metaphase II is similar to Metaphase I in that the dyads are lined up at a metaphase plate by the spindle fibers.
metaphase2
Anaphase 2
• Anaphase II separates the dyads into individual chromatids. Each sister chromatid ends up on one side of the cell.
Anaphase 2
Telophase2• At the end of Telophase II, the
nuclear envelopes forms around each set of DNA and the cytoplasm divides once again.
• As a result, four haploid cells have formed from one diploid cell. The chromosomal content of a haploid cell in one-half the chromosomal content of a diploid cell ( n as opposed to 2n )
Two Laws
• Mendel's Law of Segregation states that the 2 alleles of each gene pair separate into different gametes (egg or sperm) as these are formed prior to reproduction.
• The law of independent assortment: during gamete formation the segregation of the alleles of one allelic pair is independent of the segregation of the alleles of another allelic pair