Differentiation in somatic cells The body organs are

Differentiation in somatic cells The body organs are formed from a variety of these tissues. During cell division the nucleus of a somatic cell divides by mitosis to maintain the diploid chromosome number. Diploid cells have 23 pairs of homologous chromosomes. What is mitosis and how does it happen again? Diploid – containing 2 set of chromosomes (1 from each parent) (2 n)

Bell Work – Put these statements in order to create a flow chart of mitosis in your books Two new nuclei form Chromosomes are pulled apart Chromosomes become visible Chromosomes line up along the centre of the cell The cytoplasm splits in two DNA and other organelles replicate Chromosomes are not visible Two identical daughter cells are produced which are also identical to the parent cell

Chromosomes are not visible DNA and other organelles replicate Chromosomes become visible Chromosomes line up along the centre of the cell Chromosomes are pulled apart Two new nuclei form The cytoplasm splits in two Two identical daughter cells are produced which are also identical to the parent cell

• Recall the stages of mitosis • describe gametes as the scientific word for sex cells (sperm and eggs) • recall that meiosis is a type of cell division that produces gametes • understand why it is important that meiosis produces cells with only half the number of chromosomes of the original (parent) cell • Compare and contrast mitosis and meiosis

Every cell in the body is produced by mitosis…. …with the exception of two types of cells. . . . What do you think these cells are? Why?

23 23 46

Meiosis occurs. . • Only occurs in gametogenic areas. . • Males seminiferous tubules of testes • Females follicles in ovaries

2 n Haploid – containing 1 set of chromosomes (n) (half somatic cell) n n

Why are brothers and sisters not identical? Or sisters and sisters Or brothers and brothers

So how does meiosis happen?

Put these in the correct order. .

ANSWERS

The stages of meiosis are; 1) The chromosomes in the cell are copied (same as in mitosis). 2) All the homologous (the same type) chromosomes pair up. Cross over occurs 3) One from each pair move to opposite sides of the cell leading to 2 daughter cells being produced. These are diploid cells containing 23 pairs of chromosomes. 4) Each daughter cell then divides again to form 4 other daughter cells. These are the sex cells. They are haploid cells containing just 23 chromosomes. Meiosis

1. What affect does the relative sizes of the male and female gametes on behaviour of individuals? 2. What is the difference between a haploid and a diploid cell? 3. Why is the egg cell bigger? 4. Why is in-breeding so harmful? 5. Since this is sexual reproduction, what is asexual reproduction?

Mitosis How many cell divisions? How many daughter cells are produced? What are they like compared to the parent cell? What types of cells does this process produce? Meiosis

Key Questions 1. What is the difference between a haploid and a diploid cell? 2. Since this is sexual reproduction, what is asexual reproduction? 3. Where does meiosis happen?

Use relevent words to use each of the letters in meiosis M E I O S I S P E R M

Which stage is this?