Meiosis Say what?!? Only 5 Mondays until finals?! Work with ALL of your teachers to get late work in!

Holding Hands When a man and a woman love each other very much… And they are financially stable… And they are in a committed relationship… Only then will they get together and hold hands. After holding hands for a long time… The two people decide to combine chromosomes… Combining their chromosomes will allow them to produce a new organism Let’s call this organism a “baby” But first, they run into two problems…

Healthy Baby = 46 chromosomes Problem #1… The man inherited 23 chromosomes from his mom and 23 chromosomes from his dad. This woman inherited 23 chromosomes from her mom and 23 chromosomes from her dad . Each of them have 46 individual chromosomes in their somatic cells. If they combine their somatic cells, how many chromosomes would that give the baby? Healthy Baby = 46 chromosomes NOT 92 chromosomes 23 pairs of chromosomes

Problem #2… Not Clones Genetic diversity and variation is critical to the ongoing survival of our species. Somatic cells make EXACT copies of their DNA during mitosis. Babies are NOT clones of their parents How do we ensure that our babies are unique from ourselves? Also not clones Unsure…

MEIOSIS! Somatic cells use MITOSIS to reproduce GAMETES (sperm, eggs) use MEIOSIS to reproduce Meiosis will… #1: Divide the chromosomal count in half #2: Recombine and independently assort chromosomes

Somatic Cells Reproduce using MITOSIS Somatic cells are BODY CELLS Somatic cells are diploid. “Di” is a root word that means “two” Diploid = two copies of each chromosome. Diploid = 2n Total chroms. = 46 (2*23) Reproduce using MITOSIS

Gamete Cells Gametes are sex cells, aka germ cells Gametes are haploid Haploid cells have one copy of each chromosome Haploid = n “Hap” sounds a bit like “Half”…Haploid cells have half as many chromosomes as diploid cells Total chroms. = 23 Reproduce using MEIOSIS

Two halves make a whole Gametes are haploid Two halves make a whole Two haploid cells fuse to make one diploid cell 23 chromosomes from mom and 23 chromosomes from dad gives you 46 total chromosomes TADA! Happy diploid cells!

How do gametes form? There are TWO nuclear divisions

Making Gametes Spermatogenesis Oogenesis Results in four sperm Produces one egg Produces 3 “polar bodies” Cytoplasm divides unevenly Egg provides cellular machinery Ribosomes Mitochondria

Asexual vs. Sexual Reproduction Can reproduce faster Don’t need to find a partner All are identical Disease can easily wipe out population Sexual Allows for variation Allows for quicker adaptation to the environment Population is more resilient

Source of Genetic Variation Crossing over Independent Assortment Shuffles genetic material

Independent Work Genetic Vocabulary Worksheet Study for a vocabulary quiz next class Collect missing assignments Work on missing assignments