MEIOSIS

WHAT ARE THE PURPOSES OF MEIOSIS? TO MAKE GAMETES (EGGS AND SPERM) 2. TO REDUCE THE NUMBER OF CHROMOSOMES IN GAMETE CELLS BY ONE-HALF 3. TO INCREASE THE GENETIC DIVERSITY IN GAMETES

Chromosomes are found in pairs: Human Karyotype

Each pair is a homologous pair:

Homologous pairs of chromosomes have genes for the same traits at the same location on the chromosome

One chromosome of a homologous pair comes from the organism’s mother, and the other comes from the organism’s father

Cells where all the chromosomes are in pairs are called DIPLOID, which means they have TWO of each chromosome Abbreviated ‘2N’, where N = the number of pairs of chromosomes Humans have 23 pairs of chromosomes, so in humans 2N = 46 In humans, ALL cells except for eggs and sperm are 2N Egg and sperm only have ONE chromosome from each pair (half of the chromosomes, so they are called HAPLOID cells, abbreviated ‘N’

How do cells make haploid cells from diploid cells? Meiosis! (pronounced my-osis) In meiosis, the number of chromosomes is reduced by one-half AND genetic diversity is increased

Meiosis has two sets of divisions called Meiosis I and Meiosis II

MEIOSIS I

TETRAD FORMATION:

INTERPHASE II: NO DNA REPLICATION!

MEIOSIS II

So, from one diploid (2N) cell, meiosis makes: FOUR haploid (N) cells And ALL of those haploid cells are genetically different (have different DNA)