Download 1 - GENETICS- Mitosis Lesson

1 ­ GENETICS­ Mitosis Lesson
Genetics
Types of Cell Reproduction
• Asexual Reproduction involves a single cell dividing to make two new, identical daughter cells
> based on the process of MITOSIS
> examples include: budding; spore formation; binary fission
• Sexual Reproduction involves two cells (egg & sperm) joining together to make a new cell (zygote) that is NOT genetically identical to the original cells
> based on the process of MEIOSIS
Chromosomal Organization
• The hereditary/genetic material in the nucleus of cells is made up of long strand of DNA that are condensed, folded, and in association with proteins, formed into CHROMOSOMES.
• Prior to undergoing duplication chromosomes are found in the unduplicated form in which they appear as a single strand.
• Each chromosome must be duplicated prior to the start of mitosis. The original chromosomes and its duplicate are attached to each other by a structure called a centromere.
• In the duplicated form, a single chromosome appears as two strands and a centromere. These two strands are referred to as sister chromatids.
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1 ­ GENETICS­ Mitosis Lesson
The Cell Cycle and Mitosis
Cells need to divide because … • Cells die and need to be replaced • Cells reach a maximum size. (In order to grow any larger, an organism needs to create more cells.) • Organisms need to create offspring to continue the population of a species.
The process of Cell Division is done through MITOSIS and CYTOKINESIS.
Normal cells go through the cell cycle.
The Cell Cycle and Mitosis
The cell cycle has phases.
The first phase, Interphase, is NOT a part of cell division (mitosis or meiosis). Interphase can be divided into Three Phases: 1. G1 Phase ­ Period of normal metabolic cellular activities;
the number of organelles and amount of cytoplasm in a the cell increase. 2. S Phase ­ The Genetic Material (DNA) is replicated. The Chromosomes of the cell replicate (in humans, there will now be 92). 3. G2 Phase ­ Structures directly involved with mitosis are formed. Facts about Interphase:
­ Interphase is the longest phase in the cell cycle of a typical cell. ­ Interphase is where the cell grows and develops into a mature functioning cell.
­ DNA is replicated during the S phase of interphase to prepare the cell for division. ­ The replicated DNA exists as uncondensed fibres called chromatin.
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1 ­ GENETICS­ Mitosis Lesson
The Cell Cycle and Mitosis
Mitosis - Nuclear Division
Mitosis: is the stage of the cell cycle during which a cell's nucleus and genetic material divide.
spindle fibres
forming
spindle fibres
centromere
Mitosis: Nuclear Division
Prophase: •
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The chromatin (unwound in interphase) condenses into chromosomes. Each chromosome consists of two sister chromatids.
The chromatids are held in place by the centromere. At the end of prophase, the nuclear envelope breaks down. Spindle fibres are formed from the centrosome/centriole
Metaphase : • The chromosomes align at the equatorial plate (equator)
• The chromosomes are held in place by spindle fibres and to part of the centromere. Anaphase • The centromeres split apart.
of the • Sister chromatids separate and move toward opposite poles cell. Telophase: spindle fibres • Daughter chromosomes arrive at the poles and the disappear. • The condensed chromatin unwinds and the nuclear envelope reappears. 3
1 ­ GENETICS­ Mitosis Lesson
Cytokinesis
• Takes place after telophase
• involves the equal division of the cytoplasm and organelles among each daughter cell.
In Animals
• a cleavage furrow forms separating daughter cells
In Plants
• a cell plate forms, which eventually becomes a cell wall, separating daughter cells
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1 ­ GENETICS­ Mitosis Lesson
Aftermath of Mitosis
• the products of mitosis are two daughter cells that have the exact same genetic information and the exact same number and type of chromosomes as the parent cell
• if any of the daughter cells produced by mitosis were to receive an incorrect number of chromosomes, due to some malfunction in cell division, they would be abnormal and might not survive
• a very important process takes place after cell division called DIFFERENTIATION which is responsible for the differences that occur among different cell types
• all the cells of a multicellular organism possess the exact same genetic information in their nuclei, however each specialized cell or cell types (i.e. nerve cell, muscle cell, skin cell, bone cell, etc.) has its own specific function, dictated by the expression or "turning on" of specific genes (unique sequences of DNA)
> for example:
– a bone cell is 'directed' to be a bone cell by the "turning on" of specific genes that code for bone proteins that will allow it to carry out bone function
– a nerve cell is 'directed' to be a nerve cell by the "turning on" of specific genes that code for nerve proteins responsible for nerve cell operations
• thus, even though a specialized cell of a multicellular organism contains the complete set of genetic information, not all of the information is used by that cell ­ a muscle cell only "pays attention to" the DNA part (genes) that codes for proteins responsible for that muscle cell's function
• mitosis happens in body cells called somatic cells • each type of organism has a characteristic number of chromosomes present in each of its somatic cells
> for example:
– all human somatic cells contain 46 chromosomes (23 from mom and 23 from dad)
– fruit flies have 8
– pea plants have 14
– goldfish have 94
• this number that is found in the somatic cells of organisms is called the diploid number
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