We must reduce our chromosomes ……or else!!

Each human baby gets a copy of every single gene from its parents in an egg and sperm cell… 23 chromosomes come from mom 23 chromosomes come from dad This totals 46 chromosomes When organisms make gametes (sex cells), they need to be able to reduce the number of chromosomes in half. This process is called Meiosis – reduction division. We reduce chromosomes by dividing. Chromosome Number

We do this in two divisions called meiosis I and meiosis II Each division reduces the chromosomes in half in the baby! Specialized sex cell. Meiosis begins with a specialized sex cell containing 46 chromosmes. Meiosis

Meiosis I and Meiosis II In order to get the right number of chromosomes we must go through P, M, A, T….TWICE!

Crossing over Sometimes during Meiosis 1, doubled chromosomes called tetrads get tangled up and exchange genes. This is why you don’t look exactly like your parents.

Vocabulary Diploid cell – A cell that has the full number of chromosomes. For example, heart cells, liver cells, skin cells, etc. We call these cells 2N cells. Haploid cell – A cell that has half the number of chromosomes. For example egg and sperm cells We call these cells 1N cells.

Males vs. Females Males produce 4 sperm for each specialized sex cell. Women only produce one egg for each specialized sex cell. The other three are called polar bodies and disintegrate.

Let’s suppose that A= curly hair a = straight hair. You get one gene from Mom in an egg cell. (A) You get one gene from dad in the sperm cell (a). What kind of hair would you have? How it works………