Where were we and where are we going next? Cellular Reproduction Chapter 9

Overview of Cell Division – Mitosis and Meiosis Asexual and Sexual Reproduction Diploid vs. Haploid Cellular Reproduction Chapter Cellular Growth

Mitosis Asexual reproduction Growth and repair Somatic chromosomes (body chromosomes) Diploid (2n) No Crossing Over Produces identical daughter cells Meiosis Sexual Reproduction Passing of genetic traits Sex chromosomes aka gametes (X and Y) Haploid (n) Crossing Over Produces genetically different daughter cells Cellular Reproduction Chapter 9

Asexual Reproduction No genetic diversity Can refer to the production of offspring from one parent (binary fission in bacteria) Produces two identical offspring Susceptible to diseases and changing environments Sexual Reproduction Genetic diversity Production of gametes to fuse with another gamete (XX or XY) Produces genetically different offspring Ability to adapt to change in environments Cellular Reproduction Chapter 9

Haploid Refers to one set of chromosomes (n) Humans have ___ chromosomes Haploid would be ____ Fruit fly have ___ chromosomes Haploid would be ____ Diploid Refers to two sets of chromosomes (2n) Humans have ___ chromsomes Diploid would be ____ Fruit fly have ___ chromosomes Diploid would be ____ Cellular Reproduction Chapter 9

What are chromosomes? Chromosomes are rod-shaped structures made up of DNA and proteins. Two chromatids make up a chromosome Centromeres are attachment points for two chromatids and hold them together Chromatin are less tightly coiled DNA-protein complex used to form chromosomes Cellular Reproduction Chapter 9

Confused yet? Cellular Reproduction Chapter 9 Condensed, duplicated chromosome chromatid centromere

The Cell Cycle  The main purpose of cell division – to grow and heal certain injuries. Cellular Reproduction  Cells reproduce by a cycle of growing and dividing called the cell cycle. Chapter Cellular Growth

Cell cycle in three different stages Cellular Reproduction Chapter 9

 Interphase is the stage during which the cell grows, carries out cellular functions, and replicates.  Mitosis is the stage of the cell cycle during which the cell’s nucleus and nuclear material divide. Cellular Reproduction Chapter Cellular Growth  Cytokinesis is the method by which a cell’s cytoplasm divides, creating a new cell.

Cellular Reproduction The Stages of Interphase  The first stage of interphase, Gap 1  The cell is growing, carrying out normal cell functions, and preparing to replicate DNA. Chapter Cellular Growth

Cellular Reproduction The Second Stage of Interphase, S [Synthesis]  The cell copies its DNA in preparation for cell division. Chapter Cellular Growth

Cellular Reproduction The Third Stage of Interphase, Gap 2  The cell continues to grow and prepares for the division of its nucleus. Chapter Cellular Growth

9.2 Mitosis and Cytokinesis Cellular Reproduction The Stages of Mitosis  Prophase  The cell’s chromatin tightens.  Sister chromatids are attached at the centromere. Chapter 9  Two chromatids become one chromosome.  Spindle fibers form in the cytoplasm.

Cellular Reproduction  The nuclear envelope begins to disappear.  Spindle fibers attach to the sister chromatids. Chapter Mitosis and Cytokinesis

Cellular Reproduction Metaphase  Sister chromatids are pulled along the spindle apparatus towards the center.  They line up in the middle of the cell. Chapter Mitosis and Cytokinesis

Cellular Reproduction Anaphase  The spindle apparatus begin to shorten.  The sister chromatids separate.  The chromosomes move toward the poles of the cell. Chapter Mitosis and Cytokinesis

Cellular Reproduction Chapter Mitosis and Cytokinesis  The sister chromatids now become separate chromosomes.

Cellular Reproduction Telophase  Two new nuclear membranes begin to form and the nucleoli reappear.  The spindle apparatus disassembles. Chapter Mitosis and Cytokinesis  The pinching between the newly formed cells (called a cleavage furrow) is an indication of telophase.

Cellular Reproduction Chapter Mitosis and Cytokinesis

Cellular Reproduction Cytokinesis  In animal cells, microfilaments constrict, or pinch, the cytoplasm.  In plant cells, a new structure, called a cell plate, forms. Chapter Mitosis and Cytokinesis

Cellular Reproduction Chapter Mitosis and Cytokinesis  Division of two IDENTICAL daughter cells with the same amount of chromosomes (DNA).

Cellular Reproduction Quality Control Checkpoints  The cell cycle has built-in checkpoints that monitor the cycle and can stop it if something goes wrong. Chapter Cell Cycle Regulation

Cellular Reproduction Abnormal Cell Cycle: Cancer  Cancer is the uncontrolled growth and division of cells.  Cancer cells can kill an organism by crowding out normal cells, resulting in the loss of tissue function. Chapter Cell Cycle Regulation

Cellular Reproduction Causes of Cancer  Mutations that cause problems in the regulation of cell growth and division  Various environmental factors can affect the occurrence of cancer cells. Chapter Cell Cycle Regulation

 Human body cells have 46 chromosomes 10.1 Meiosis Sexual Reproduction and Genetics  Each parent contributes 23 chromosomes Chapter 10  Homologous chromosomes—one of two paired chromosomes, one from each parent Chromosomes and Chromosome Number

Homologous chromosomes 10.1 Meiosis Sexual Reproduction and Genetics  Same length  Same centromere position  Carry genes that control the same inherited traits Chapter 10

Haploid and Diploid Cells  Human gametes contain 23 chromosomes. Sexual Reproduction and Genetics  A cell with n chromosomes is called a haploid cell.  A cell that contains 2n chromosomes is called a diploid cell Meiosis  An organism produces gametes to maintain the same number of chromosomes from generation to generation. Chapter 10

Meiosis I  The sexual life cycle in animals involves meiosis. Sexual Reproduction and Genetics  Meiosis produces gametes Meiosis  When gametes combine in fertilization, the number of chromosomes is restored. Chapter 10

Stages of Meiosis I  Reduces the chromosome number by half through the separation of homologous chromosomes Sexual Reproduction and Genetics  Involves two consecutive cell divisions called meiosis I and meiosis II 10.1 Meiosis Chapter 10

Meiosis I Sexual Reproduction and Genetics 10.1 Meiosis  Interphase  Chromosomes replicate.  Chromatin condenses. Chapter 10 Interphase

Meiosis I Sexual Reproduction and Genetics 10.1 Meiosis  Prophase I  Pairing of homologous chromosomes occurs.  Each chromosome consists of two chromatids.  The nuclear envelope breaks down.  Spindles form. Chapter 10 Prophase I

Meiosis I Sexual Reproduction and Genetics 10.1 Meiosis  Prophase I  Crossing over produces exchange of genetic information.  Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes. Chapter 10

Meiosis I Sexual Reproduction and Genetics 10.1 Meiosis  Metaphase I  Chromosome centromeres attach to spindle fibers.  Homologous chromosomes line up at the equator. Chapter 10 Metaphase I

Meiosis I Sexual Reproduction and Genetics 10.1 Meiosis  Anaphase I Chapter 10 Anaphase I  Homologous chromosomes separate and move to opposite poles of the cell.

Meiosis I Sexual Reproduction and Genetics 10.1 Meiosis  Telophase I  The spindles break down.  Chromosomes uncoil and form two nuclei.  The cell divides. Chapter 10 Telophase I

Meiosis II  Prophase II Sexual Reproduction and Genetics 10.1 Meiosis Chapter 10  A second set of phases begins as the spindle apparatus forms and the chromosomes condense. Prophase II

Meiosis II  Metaphase II Sexual Reproduction and Genetics 10.1 Meiosis Chapter 10  A haploid number of chromosomes line up at the equator. Metaphase II

Meiosis II Sexual Reproduction and Genetics 10.1 Meiosis  Anaphase II Chapter 10 Anaphase II  The sister chromatids are pulled apart at the centromere by spindle fibers and move toward the opposite poles of the cell.

Sexual Reproduction and Genetics 10.1 Meiosis Meiosis II Chapter 10  Telophase II  The chromosomes reach the poles, and the nuclear membrane and nuclei reform. Telophase II

Meiosis II Sexual Reproduction and Genetics  Cytokinesis results in four haploid cells, each with n number of chromosomes Meiosis Chapter 10 Cytokinesis

The Importance of Meiosis  Meiosis consists of two sets of divisions Sexual Reproduction and Genetics  Produces four haploid daughter cells that are not identical 10.1 Meiosis  Results in genetic variation Chapter 10

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 Meiosis Chapter 10

Sexual Reproduction and Genetics 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  Beneficial genes multiply faster over time Meiosis Chapter 10