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Transcript
MEIOSIS & MITOSIS Noadswood Science, 2012 Tuesday, May 23, 2017 MEIOSIS & MITOSIS To understand meiosis & mitosis SIZE NUCLEUS The genetic information passed from parent to offspring is contained in genes, carried by chromosomes in the nucleus All body cells have a nucleus which contains all genetic information nucleus CHROMOSOMES & GENES A gene is a section of DNA that carries the code for a particular protein (made from joined amino acids) Different genes control the development of different characteristics of an organism – many genes are needed to carry all the genetic information for a whole organism Chromosomes, found in the cell nucleus, contain many genes DNA Chromosomes and their genes are made of a molecule called DNA DNA molecules carry the code that controls what your cells are made of and what they do Each chromosome is a very long molecule of tightly coiled DNA MITOSIS Mitosis is the type of cell division that leads to growth or repair When a cell divides by mitosis: Two new cells form Each cell is identical to the other one, and the cell they were formed from MITOSIS STAGES 1. Parent cell 2. Chromosomes make identical copies of themselves 3. They line up along the centre 4. They split 5. They move apart 6. Two daughter cells form with identical chromosomes to the parent cell MEIOSIS Gametes are formed from cells in the reproductive organs by a type of cell division called meiosis Male Female Reproductive Organs Testes Ovaries Gametes Sperm Egg MEIOSIS The cells that are formed by meiosis have half as many chromosomes as the cell that formed them Human body cells contain 23 pairs of chromosomes, while human gametes contain 23 single chromosomes The main features of meiosis are: The chromosomes are copied The cell divides twice, forming four gametes MEIOSIS STAGES GENDER Human body cells have 23 pairs of chromosomes in the nucleus – one of these pairs controls the inheritance of gender (whether offspring are male or female) In males, the two sex chromosomes are different – XY In females, the two sex chromosomes are the same – XX Male – XY Female – XX GAMETES & FERTILISATION Gametes are sex cells – the male gametes are the sperm, and the female gametes are the eggs Gametes contain one set of genetic information, while body cells contain two sets of genetic information Fertilisation is the joining or fusion of a male gamete and a female gamete – the new cell that is formed divides over and over again by mitosis creating the many cells that eventually form a new individual OBSERVATIONS Using the microscopes look at some cells which are currently undergoing mitosis / meiosis…