Sexual Reproduction and Genetics Section 1- Meiosis Chapter 10 Sexual Reproduction and Genetics Section 1- Meiosis

Chromosomes and Chromosome Number Section 1 - Meiosis Sexual Reproduction and Genetics Chromosomes and Chromosome Number Human body cells have 46 chromosomes. Each parent contributes 23 chromosomes. Homologous chromosomes—one of two paired chromosomes, one from each parent.

Chromosomes and Chromosome Number Section 1 - Meiosis Sexual Reproduction and Genetics Chromosomes and Chromosome Number Homologous Chromosomes: Same length. Same centromere position. Carry genes that control the same inherited traits.

Haploid and Diploid Cells Section 1 - Meiosis Sexual Reproduction and Genetics Haploid and Diploid Cells An organism produces gametes to maintain the same number of chromosomes from generation to generation. Human gametes contain 23 chromosomes. A cell with n chromosomes is called a haploid cell. A cell that contains 2n chromosomes is called a diploid cell.

The sexual life cycle in animals involves meiosis. Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis The sexual life cycle in animals involves meiosis. Meiosis produces gametes. When gametes combine in fertilization, the number of chromosomes is restored (back to 2n – diploid).

Meiosis is a reduction division. Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis Meiosis is a reduction division. In other words, it reduces the chromosome number by half through the separation of homologous chromosomes. In humans - from 46 chromosomes to 23. Meiosis involves two consecutive cell divisions called meiosis I and meiosis II.

Chromosomes replicate. Synthesis of proteins. Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis I Interphase Chromosomes replicate. Synthesis of proteins.

Meiosis I Prophase I Chromosomes coil and condense. Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis I Prophase I Chromosomes coil and condense. Pairing of homologous chromosomes occurs. Each chromosome consists of two chromatids. The nuclear envelope breaks down. Centrioles moves toward poles. Spindles form and bind to centromeres.

Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis I Prophase I Crossing over produces exchange of genetic information. Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.

Homologous chromosomes line up at the equator of the cell. Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis I Metaphase I Homologous chromosomes line up at the equator of the cell.

Meiosis I Anaphase I Homologous chromosomes separate and move to Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis I Anaphase I Homologous chromosomes separate and move to opposite poles of the cells. Chromosome # is reduced from 2n to n when homologous chromosomes separate.

The spindles break down. Chromosomes uncoil and form two nuclei. Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis I Telophase I The spindles break down. Chromosomes uncoil and form two nuclei. The cell divides.

apparatus forms and the chromosomes condense. Section 1 – Meiosis Sexual Reproduction and Genetics Meiosis II Prophase II A second set of phases begins as the spindle apparatus forms and the chromosomes condense.

Meiosis II Metaphase II A haploid number of chromosomes line up Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis II Metaphase II A haploid number of chromosomes line up at the equator.

Meiosis II Anaphase II The sister chromatids are pulled apart at the Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis II Anaphase II The sister chromatids are pulled apart at the centromere by spindle fibers and and move toward the opposite poles of the cell.

Meiosis II Telophase II The chromosomes reach Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis II Telophase II The chromosomes reach the poles, and the nuclear membrane and nuclei reform.

Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis II Cytokinesis results in four haploid cells, each with n number of chromosomes.

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The Importance of Meiosis Section 1 - Meiosis Sexual Reproduction and Genetics The Importance of Meiosis Meiosis consists of two sets of divisions. Produces four haploid daughter cells that are not identical. Results in genetic variation.

Section 1 - Meiosis Sexual Reproduction and Genetics Meiosis Provides Variation Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result. Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine.

Law of Independent Assortment Section 2 - Meiosis Sexual Reproduction and Genetics Law of Independent Assortment Random distribution of alleles occurs during gamete formation. Genes on separate chromosomes sort independently during meiosis. Each allele combination is equally likely to occur.

Law of Independent Assortment Section 2 - Meiosis Sexual Reproduction and Genetics Law of Independent Assortment Two pairs of homologous chromosomes can be arranged in two different ways at meiosis I of meiosis. These arrangements occur randomly, with approximately half the meiotic cells oriented one way and the other half oriented the opposite way.

Independent Assortment Section 2 – Mendelian Genetics Sexual Reproduction and Genetics Independent Assortment

Section 2 - Meiosis Sexual Reproduction and Genetics Crossing Over During prophase I, nonsister chromatids of homologous chromosomes exchange pieces of genetic material. As a result each homologue no longer entirely represents a single parent.

Section 2 - Meiosis Sexual Reproduction and Genetics Crossing Over Free ends of one maternal and one paternal chromatid wrap around each other at one or more points. Crossover allows the paired maternal and paternal chromosomes to exchange genetic material.

Sexual Reproduction and Genetics Mitosis vs. Meiosis

Take out your book and copy Table 1 from page 275. Sexual Reproduction and Genetics Mitosis vs. Meiosis Mitosis vs. Meiosis Take out your book and copy Table 1 from page 275. Mitosis Meiosis