Meiosis Gamete Production

Meiosis Similar in many ways to mitosis Several differences however Involves 2 cell divisions Results in 4 cells with 1/2 the normal genetic information. Vocabulary: Diploid (2N) - Normal amount of genetic material Haploid (N) - 1/2 the genetic material.

Meiosis In Humans, these are the Ova (egg) and sperm. Meiosis results in the formation of haploid cells. In Humans, these are the Ova (egg) and sperm. Ova are produced in the ovaries in females Process is called oogenesis Sperm are produced in the testes of males. Process is called spermatogenesis Meiosis occurs in 2 phases: Meiosis I & Meiosis II

Spermatogenesis & Oogenesis Sperm formation Egg formation

Why Do we Need Meiosis? It is the fundamental basis of sexual reproduction Two haploid (n) gametes are brought together through fertilization to form a diploid (2n) zygote

Fertilization – “Putting it all together”

Meiosis I Prior to division (S phase), amount of DNA doubles

Replication of Chromosomes Replication of DNA occurs Occurs prior to division (S of Interphase) Replicated copies are called sister chromatids Held together at centromere Occurs in Interphase Replication is the process of duplicating chromosome. The new copy of a chromosome is formed by DNA synthesis during S-phase. The chromosome copies are called sister chromatids. Sister chromatids are held together at the centromere.

Prophase I Genes are exchanged at these connections Areas of homologous chromosomes connect at areas called CHIASMATA Genes are exchanged at these connections

Prophase I Homologous (same genes, different alleles) Gene X Sister Chromatids (same genes, same alleles) Homologous (same genes, different alleles)

Crossing Over Segments of homologous chromosomes break and reattach at similar locations. Results in new genetic combinations of offspring. This is the main advantage of sexual reproduction

Chiasmata

Anaphase I During Anaphase I, each HOMOLOGOUS CHROMOSOME is pulled to opposite sides of the cell. Unlike mitosis, the CENTROMERES DO NOT BREAK. Nuclei reform in Telophase I CYTOKENESIS occurs, results in 2 cells, but these cells still contain sister chromatids paired together.

Meiosis II DNA DOES NOT double Chromosomes randomly line-up along metaphase plate like regular mitosis. During Anaphase II, CENTROMERES BREAK and each SISTER CHROMATID is pulled to opposite sides of the cell. Nuclei reform and cytokinesis usually occurs (although it is often unequal). Sister chromatids

Meiosis: Two Part Cell Division Sister chromatids separate Homologous Chromosomes separate Meiosis I Meiosis II Diploid Diploid Haploid

Overview of Meiosis