Meiosis Chapter 8

Two Types of Reproduction Asexual Reproduction 1 parent Identical DNA Process: Mitosis Sexual Reproduction 2 parents Different DNA Combo of 2 organisms Process: Meiosis

DNA

Homologous Chromosomes chromosomes with the same genes

Chromosome # Diploid Haploid homologous chromosomes Complete set Body cells Haploid One member of pair ½ set Gametes Egg or Sperm

Fertilization 23 46 23 Fertilized egg – zygote process by which an egg and sperm unite 23 Zygote develops into embryo (early stage of development) and finally adult organism by mitosis 46 Haploid 23 Fertilized egg – zygote Diploid

Fertilized egg – zygote Without meiosis ………… Fertilized egg – zygote 46 92 46

Meiosis: A reduction division

Prophase I Chromosomes condense Nuclear envelope breaks Spindle forms Tetrads form

Tetrads A pairing of homologous chromosomes Four chromatids

Prophase I Crossing over occurs Exchange genetic material Why? Increase variation

Metaphase I Tetrads line up in the middle of the cell

Anaphase I Tetrads separate & chromosomes move towards poles

Telophase I Nuclues reforms Spindle dissappears Two new cells are formed

Meiosis II: Reducing Chromosome Number

Results of Meiosis Gametes (egg & sperm) form Four haploid cells with one copy of each chromosome Different combinations of alleles due to crossing over GENETICALLY DIFFERENT

Sperm Formation

Egg Formation (unequal cytokinesis)

Mitosis Vs. Meiosis Characteristic Mitosis Meiosis #divisions 1 2 #daughter cells 4 Ploidy beginning Diploid Ploidy end Haploid Purpose Growth/replace Reproduction Where occurs? Body cells (Somatic) Gametes