Meiosis is Necessary for Sexual Reproduction 3 Sexual Reproduction –Meiosis I 3 Prophase I – 2 Metaphase I – 2 Anaphase I – 2 Telophase I –Meiosis II 2 Prophase II – 2 Metaphase II – 2 Anaphase II – 2 Telophase II –4 The Why and Where of Meiosis -
Unit IV Genetics LEARNING GOAL 2RELATE THE PROCESS OF MEIOSIS TO THE INHERITANCE OF GENETIC TRAITS.
Meiosis is Necessary for Sexual Reproduction Sexual Reproduction Reproductive method of most plants and animals. Gametes (sex cells) from opposite sexes unite to form a zygote (fertilized egg). A zygote is a diploid cell (full chromosome set) so the number of chromosomes in the gametes must be half (haploid). Meiosis results in gamete production.
Meiosis IProphase I Same as prophase of mitosis except chromosomes form homologous pairs. Homologous means that the chromosomes contain genes for the same traits and one member of the pair came from the mother and one from the father. Homologs may exchange sections of chromosomes at this stage which is called crossing over.
Metaphase I Homologous pairs move to center of cell. Each homolog still consists of two chromatids.
Anaphase I Homologs separate. Chromatids of each homolog stay together.
Telophase I Chromosomes gather at opposite poles of cell, then cytokinesis occurs. Each cell now has half the original number of chromosomes.
Meiosis IISame as mitosis.Prophase IIChromosomes are still doubled and become visible.
Metaphase II Replicated chromosomes line up in the middle.
Anaphase II Sister chromatids are pulled apart at the centromeres.
The Why and Where of Meiosis Results in the production of male and female gametes (sperm and egg). Produces haploid cells so that the diploid number can be restored upon fusion of gametes during fertilization. Occurs in cells of the reproductive organs, testes in males and ovaries in females. Creates genetic variation due to crossing over and shuffling of homologous chromosome pairs.