Unit 4: Reproduction Traits Traits: are physical features of an organism. They can vary in size or form from one individual to another. Examples include eye color, height and colour vision. Heredity Heredity: is the process through which trait patterns are passed from parents to their offspring. Heredity explains why offspring share features with other family members. Nucleus: The Control Center Nucleus: is the cell organelle that is responsible for heredity and controlling cell activities such as cell division. The nucleus contains the organism s DNA. The nucleus contains the master set of instructions. These instructions determine what each cell will become, how it will function, when it will grow and divide, and when it will die. DNA deoxyribonucleic acid Chromosomes When a cell is ready to undergo cellular division, loosely coiled DNA folds up and becomes compacted. These compacted forms of DNA are called Chromosomes. Chromosomes are X-shaped structures. 1
Genes Genes: segments (sections) of DNA. They code for producing proteins in cells. Proteins determine what body cells will become and how they will function. Differences & Similarities: DNA, Chromosomes and Genes Mutation Gene Mutation: is a specific, and permanent change in the chemical make up of a gene. A gene mutation is a change in the sequence of A, C, G and T bases. For example, a change from ACCTTGGA to ACTTGGA may result in a malfunctioning protein. Gene mutations can, or may not be, harmful to an organism. Some mutations are beneficial. A gene mutation may result in a malfunctioning protein. Mutagens Mutagens: are substances or factors that can cause mutations. These factors result in changes to Gene Sequences. There are 2 sources of mutagens. (1) Mutagens that occur naturally. Examples include X-rays, UV rays and viruses. (2) Mutagens that are created by human activities. Examples include cigarette smoke, pollutants and radiation. Cell division Cells develop at an exponential rate. Unit 4: Reproduction MITOSIS IS THE BASIS OF ASEXUAL REPRODUCTION 2
Cell Cycle & Development It is necessary for cells to divide, producing more cells, as an organism develops. Cells die and need to be replaced. Cells that take a lot of wear and tear, including skin cells, stomach cells and intestinal cells need to be replaced. The Cell Cycle ensures that body cells are replaced and the overall health of the organism is maintained. Cell Cycle Stages Cell Cycle: is a series of three stages in the life of a cell. The cycle involves cellular division to produce more identical cells. The 3 stages of the Cell Cycle are: 1. Interphase 2. Mitosis 3. Cytokinesis Stage 1: Interphase Stage 1: Interphase Interphase: is the first and longest stage of the cell cycle. During this stage the cell carries out its various functions and prepares for division. During Interphase the cell doubles all of its material, including its DNA in preparing for division. The process of doubling the amount of DNA in interphase is called Replication. Stage 2: Mitosis Mitosis: the second, and usually the shortest stage of the cell cycle, involves the division of a cell s nucleus producing two identical daughter cells. Stages of Mitosis Mitosis involves 4 distinct stages or steps. The 4 stages of Mitosis, in order, are: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase 3
Prophase During prophase the double stranded chromosomes shorten and thicken. The nuclear membrane that surrounded the nucleus breaks down and disappears. Metaphase During metaphase chromosomes line up across the middle (or equator) of the cell. Anaphase During anaphase chromosomes are pulled to opposite ends (poles) of the cell. The chromosomes are pulled at their centers. Telophase At telophase, the sets of chromosomes that reached opposite poles form nuclei. They cell is now ready to divide into two identical daughter cells. Stage 3: Cytokinesis Cytokinesis: is the final stage of the cell cycle. Once mitosis is complete, the cell membrane pinches together and the cell divides into two identical daughter cells. The products of Mitosis Mitosis results in one parent cell dividing to produce two identical daughter cells which have the same number of chromosomes as the parent cell. How many brain cells originally underwent cell division to produce 24 brain cells? A cell divides by mitosis once every two hours. How many of these cells will be produced after an 8 hour period? 4
Checkpoints in the Cell Cycle Special proteins at checkpoints monitor cell activities and send this information along to the nucleus. At each checkpoint, the nucleus instructs the cell whether or not to divide. A cell will stop undergoing division if: Not enough nutrients for cell growth Replication of DNA did not occur DNA is damaged 5