Transcript Meiosis
Meiosis B3d OBJECTIVES Key Objective • Describe how sex cells are formed C/D • State that, at fertilisation, gametes combine to form a diploid zygote. • State that gametes are produced by meiosis. • State that gametes are haploid • State that meiosis introduces variation. • Explain how the mitochondria and acrosome of a sperm cell is adapted to its function A/B • Explain what happens to the chromosomes during meiosis STARTER • What is the scientific name for the human sex cells? • What are the male and female sex cells? • What is the name for the moment in which the sperm enters the egg? adaptation have a tail for swimming have a nucleus to carry genes produced in large numbers to increase the chance of fertilisation are large to contain a food source egg, sperm or both Eggs and sperm The female egg cell and the male sperm cell are examples of ____________ cells: The ______ cell is specialised in two ways: Nucleus The egg cell is basically an enlarged cell with massive _____ reserves Head packed with “enzymes” to ______ its way through the egg Strong tail for ________ Words – food, swimming, sperm, specialised, digest What is meiosis? Meiosis summary How does meiosis turn one cell into four new sex cells? Meiosis Each daughter cell has half the number of chromosomes of the parent. Mitosis vs. Meiosis Mitosis: Meiosis: 1. 1. Used for growth and repair of cells 2. Used in asexual reproduction 3. Cells with identical number of chromosomes and genetic information are produced Used to produce gametes for sexual reproduction 2. Each daughter cell has half the number of chromosomes of the parent PLENARY 1. Which type of cell division produces gametes? – 2. Meiosis What does meiosis introduce into the daughter cells that mitosis does not? – 3. Variation – difference in the chromosomes, or they are not identical In humans, body cells contain two pairs of 23 chromosomes – 46 in total. What name do we give to a cell that contains a pair of each chromosome? – 4. Diploid Cells produced by meiosis have only one of each chromosome. What name do we use to describe this type of cell? – 5. Haploid Describe how a zygote forms. – Nucleus of egg joins with the nucleus of a sperm EXTENSION:6. 7. Name as many differences as you can between meiosis and mitosis. Meiosis involves two different divisions. Describe what happens to the chromosomes in each division and explain how this changes the number of chromosomes in the new cells. mitosis meiosis First division – homologous pairs separate; half go to one pole and the other half to the other pole, which reduces the number of chromosomes Second division – chromosomes split as in mitosis daughter cells genetically identical daughter cells not genetically identical two daughter cells four daughter cells diploid cells form haploid cells form homologous pairs do not meet homologous pairs meet one division involves two divisions body cells form gametes form crossing over no crossing over