Cell Division Mitosis and Meiosis

Recall A Few Main Things All new cells come from existing cells DNA is stored in the nucleus of cells in eukaryotes

Chromosomes A chromosome is a single, very long, strand of DNA Each chromosome contains many thousands of genes

Diploidy Each species has a set # of chromosomes We also have 2 versions of each chromosome (called homologous chromosomes) I.e. humans have 23 sets of chromosomes, or 46 total

Types of Cell Division Usually when we make new cells, we want them to be identical to existing cells i.e. make new skin cells from existing ones The new cell is completely identical

Mitosis Cell division that creates identical daughter cells So the new cell has the exact same chromosomes as the original cell

The Extent of Mitosis Almost every single cell in our body is made from mitosis Exceptions: the first cell, sperm/egg cells When we grow new skin, new hair, new muscles – all of that is mitosis So every cell in our body has the exact same set of chromosomes

Sperm/Egg You pass on half your genes to offspring You must make a gamete (sperm or egg cell) with half of your chromosomes Each gamete randomly receives 1 of the 2 versions of each chromosome

Meiosis Each parent cell produces 4 daughter cells Each daughter cell has 1 set of chromosomes (half of the parent’s chromosomes) (is haploid)

# of Possible Gametes There are 223 possible chromosome combinations to make a gamete =8,388,608 possibilities So you are 1 out of 8,388,6082 possibilities You are quite literally 1 in a trillion (1 of 70,368,744,200,000 possible combinations of your parents)

Mitosis vs. Meiosis Mitosis Meiosis Identical offspring (same set of chromosomes) 2 daughter cells Creates all body cells Produces diploid cells Offspring have half as many chromosomes 4 daughter cells Creates sperm/egg Produces haploid cells Mitosis vs. Meiosis

What’s the Point? Meiosis allows us to have offspring that are different and have a unique combination of genes This increases diversity in the population Increased diversity means increased ability for the species to survive and adapt to new situations