Meiosis produces haploid gametes. Section 1: Meiosis K What I Know W What I Want to Find Out L What I Learned

6(G) Recognize the significance of meiosis to sexual reproduction. 3(A) In all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student. 5(A) Describe the stages of the cell cycle, including deoxyribonucleic acid (DNA) replication and mitosis, and the importance of the cell cycle to the growth of organisms. 6(A) Identify components of DNA, and describe how information for specifying the traits of an organism is carried in the DNA. Meiosis Copyright © McGraw-Hill Education

Essential Questions How does the reduction in chromosome number occur during meiosis? What are the stages of meiosis? What is the importance of meiosis in providing genetic variation? Meiosis Copyright © McGraw-Hill Education

Review chromosome New gene homologous chromosome gamete haploid fertilization diploid meiosis crossing over Meiosis Copyright © McGraw-Hill Education Vocabulary

Meiosis Copyright © McGraw-Hill Education Chromosomes and Chromosome Number Characteristics such as hair color, eye color, etc., are called traits. The instructions for each trait are located on chromosomes, in the nucleus of cells. DNA is organized in segments called genes that control the production of a protein. Each chromosome contains hundreds of genes.

Meiosis Copyright © McGraw-Hill Education Chromosomes and Chromosome Number Homologous chromosomes Human cells have 46 chromosomes, or 23 pairs (one contributed by each parent). The chromosomes that make up the pairs are called homologous chromosomes. Homologous chromosomes are the same length, same centromere position, and carry genes for the same traits.

Meiosis Copyright © McGraw-Hill Education Chromosomes and Chromosome Number Haploid and diploid cells To maintain the same number of chromosomes from generation to generation, organisms produce gametes – sex cells with half the number of chromosomes. The symbol n can be used to represent the number of chromosomes in a gamete. A cell with n chromosomes is called a haploid cell. A cell that contains 2n chromosomes is called a diploid cell.

Meiosis Copyright © McGraw-Hill Education Meiosis I Meiosis is a type of cell division that reduces the number of chromosomes in a cell and produces gametes.Meiosis i Involves two consecutive cell divisions, meiosis I and meiosis II.

Meiosis Copyright © McGraw-Hill Education Meiosis I Interphase Chromosomes replicate. Chromatin condenses.

Meiosis Copyright © McGraw-Hill Education MeiosisMeiosis I Prophase I Pairing of homologous chromosomes occurs. Each chromosome consists of two sister chromatids.

Meiosis Copyright © McGraw-Hill Education Meiosis I Prophase I As homologous chromosomes condense, they are bound together in a process called synapsis, which allows for crossing over. Crossing over – chromosomal segments are exchanged between a pair of homologous chromosomes. Crossing over produces exchange of genetic information.

Meiosis Copyright © McGraw-Hill Education Meiosis I Metaphase I Chromosome centromeres attach to spindle fibers. Homologous chromosomes line up as a pair at the equator.

Meiosis Copyright © McGraw-Hill Education Meiosis I Anaphase I Homologous chromosomes separate and move to opposite poles of the cell. The chromosome number is reduced from 2n to n when the homologous chromosomes separate.

Meiosis Copyright © McGraw-Hill Education Meiosis I Telophase I Chromosomes reach the cells opposite poles. Cytokinesis occurs.

Meiosis Copyright © McGraw-Hill Education Meiosis II Prophase II A second set of phases begins as the spindle apparatus forms and the chromosomes condense.

Meiosis Copyright © McGraw-Hill Education Meiosis II Metaphase II Chromosomes are positioned at the equator. Meiosis II involves a haploid number of chromosomes.

Meiosis Copyright © McGraw-Hill Education Meiosis II Anaphase II Sister chromatids are pulled apart at the centromere by spindle fibers and move toward the opposite poles of the cell.

Meiosis Copyright © McGraw-Hill Education Meiosis II Telophase II The chromosomes reach the poles, and the nuclear membrane and nuclei reform.

Meiosis Copyright © McGraw-Hill Education Meiosis II Cytokinesis results in four haploid cells, each with n number of chromosomes. Cytokinesis

Visualizing Meiosis Animation FPO Add link to animation from page 273 (Figure 5) here. Meiosis Copyright © McGraw-Hill Education

Meiosis Copyright © McGraw-Hill Education The Importance of Meiosis Mitosis consists of one cell division that produces identical cells Meiosis consists of two cell divisions that produce haploid daughter cells that are not genetically identical. Meiosis results in genetic variation.

Interactive Table – Mitosis and Meiosis Animation FPO Add link to interactive table from page 275 (Table 1) here. Meiosis Copyright © McGraw-Hill Education

Meiosis Copyright © McGraw-Hill Education The Importance of Meiosis Meiosis provides variation During prophase I, the chromosomes line up randomly at the equator. Gametes end up with different combinations of chromosomes. Genetic variation also is produces during crossing over and during fertilization, when games randomly combine.

Meiosis Copyright © McGraw-Hill Education Sexual Reproduction v. Asexual Reproduction Asexual reproduction The organism inherits all of its chromosomes from a single parent. The new individual is genetically identical to its parent. Sexual reproduction Rate of beneficial mutations is faster. Beneficial genes multiply faster over times than they do for asexual organisms.

Meiosis Copyright © McGraw-Hill Education Review Essential Questions How does the reduction in chromosome number occur during meiosis? What are the stages of meiosis? What is the importance of meiosis in providing genetic variation? Vocabulary gene homologous chromosome gamete haploid fertilization diploid meiosis crossing over