Fig Review of the cell cycle and mitosis late interphaseprophase prometaphase metaphaseanaphasetelophase

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.9

On the cytoplasmic side of the cleavage furrow a contractile ring of actin microfilaments and the motor protein myosin form. Contraction of the ring pinches the cell in two. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.8a

Cytokinesis in plants, which have cell walls, involves a completely different mechanism. During telophase, vesicles from the Golgi coalesce at the metaphase plate, forming a cell plate. –The plate enlarges until its membranes fuse with the plasma membrane at the perimeter, with the contents of the vesicles forming new wall material in between. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.8b

Some interesting aspects of cell division processes. This is not part of what you are required to know but I outlined. Like many things in biology certain types of compounds serve various functions. Thus actin and myosin proteins are responsible for in folding the animal cell wall to divide the cytoplasm in cytokinesis. These are also the proteins in muscle cells that contract. In order to control cell division there are a series of chemicals that turn on replication or suppress it. These can be growth factors, density dependent control factors, attachment factors, nutrients etc. There are also a whole series of factors that bring about cell death as normal process. In diseases such as cancer some of these factors are missing, suppressed or receptors are faulty and the cells continuously divided getting out of control and invading tissues through out the body with serious results All these and more are discussed in Chapter 12 of your text.

Heredity, asexual reproduction and sexual reproduction Off spring whether produced asexually or sexually receive genes from the parents. Like begets like, i.e., identical and are products of asexual reproduction. Example: Paramecium (Protista) undergoing mitosis or a multicellular organisms that buds off new individuals such as Hydra. Like begets like, but with variation resulting from sexual reproduction. What does that mean? Example: Humans produce humans but the off spring are not identical to either parent.

Offspring resemble their parents more than they do less closely related individuals of the same species. The transmission of traits from one generation to the next is called heredity or inheritance. However, offspring differ somewhat from parents and siblings, demonstrating variation. Genetics is the study of heredity and variation. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Living organisms are distinguished by their ability to reproduce their own kind. Offspring resemble their parents more than they do less closely related individuals of the same species. The transmission of traits from one generation to the next is called heredity or inheritance. However, offspring differ somewhat from parents and siblings, demonstrating variation. Genetics is the study of heredity and variation. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Parents endow their offspring with coded information in the form of genes. –Your genome is derived from the thousands of genes that you inherited from your mother and your father. Genes program specific traits that emerge as we develop from fertilized eggs into adults. –Your genome may include a gene for freckles, which you inherited from your mother. Offspring acquire genes from parents by inheriting chromosomes Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Genes are segments of DNA. Genetic information is transmitted as specific sequences of the four deoxyribonucleotides in DNA. –This is analogous to the symbolic information of letters in which words and sentences are translated into mental images. Most genes program cells to synthesize specific enzymes and other proteins that produce an organism’s inherited traits. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The transmission of hereditary traits has its molecular basis in the precise replication of DNA. –This produces copies of genes that can be passed from parents to offspring. In plants and animals, sperm and ova (unfertilized eggs) transmit genes from one generation to the next. After fertilization (fusion) of a sperm cell with an ovum, genes from both parents are present in the nucleus of the fertilized egg. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Sexual reproduction results in greater variation among offspring than does asexual reproduction. Two parents give rise to offspring that have unique combinations of genes inherited from the parents. Offspring of sexual reproduction vary genetically from their siblings and from both parents. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig Top row couples had two children each, which children belong to which couple? All pictures are from high school year book.

Many steps of meiosis resemble steps in mitosis. Both are preceded by the replication of chromosomes. However, in meiosis, there are two consecutive cell divisions, meiosis I and meiosis II, which results in four daughter cells. Each final daughter cell has only half as many chromosomes as the parent cell. Meiosis reduces chromosome number from diploid to haploid: a closer look Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Meiosis reduces chromosome number by copying the chromosomes once, but dividing twice. The first division, meiosis I, separates homologous chromosomes. The second, meiosis II, separates sister chromatids. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 13.6