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