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 egg, sperm or both 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

Eggs and sperm The female egg cell and the male sperm cell are examples of ____________ cells: The egg cell is basically an enlarged cell with massive _____ reserves The ______ cell is specialised in two ways: Words – food, swimming, sperm, specialised, digest Head packed with “enzymes” to ______ its way through the egg Strong tail for ________ Nucleus

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: 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 Meiosis: 1.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? –Meiosis 2.What does meiosis introduce into the daughter cells that mitosis does not? –Variation – difference in the chromosomes, or they are not identical 3.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? –Diploid 4.Cells produced by meiosis have only one of each chromosome. What name do we use to describe this type of cell? –Haploid 5.Describe how a zygote forms. –Nucleus of egg joins with the nucleus of a sperm

EXTENSION:- 6.Name as many differences as you can between meiosis and mitosis. 7.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. mitosismeiosis daughter cells genetically identical daughter cells not genetically identical two daughter cellsfour daughter cells diploid cells formhaploid cells form homologous pairs do not meet homologous pairs meet one divisioninvolves two divisions body cells formgametes form crossing overno crossing over 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