Meiosis Noadswood Science, 2016

Meiosis Sunday, May 27, 2018 To explain the process of meiosis

Precise Learning Students should understand that meiosis leads to non-identical cells being formed while mitosis leads to identical cells being formed. Students should be able to explain how meiosis halves the number of chromosomes in gametes and fertilisation restores the full number of chromosomes. Cells in reproductive organs divide by meiosis to form gametes.   Gametes join at fertilisation to restore the normal number of chromosomes. The new cell divides by mitosis. The number of cells increases. As the embryo develops cells differentiate (knowledge of the stages of meiosis is not required)

Recapping 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 Parent cell Chromosomes make identical copies of themselves They line up along the centre They split They move apart 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

Meiosis

Meiosis

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…

Meiosis & Mitosis Comparison

Practice Questions How many sets of chromosomes do gametes have? Where are gametes produced? How many cell divisions occur in meiosis? How many new cells are produced when a cell divides by meiosis? True or false – all gametes are genetically identical Following fertilisation, how does the resulting cell grow?

Answers How many sets of chromosomes do gametes have – 1 Where are gametes produced – reproductive organs How many cell divisions occur in meiosis – 2 How many new cells are produced when a cell divides by meiosis – 4 True or false – all gametes are genetically identical – false Following fertilisation, how does the resulting cell grow – via mitosis