Meiosis What came first, the chicken or the Egg? We learned last semester that mitosis creates new identical cells but before we can have a chicken we must have an egg. Meiosis explains how this happens. Student Expectation: RECOGNIZE the significance of meiosis to sexual reproduction;

1. How many chromosomes do you have in healthy cells? Somatic Body cells Blood, skin, hair, bone 46 chromosomes Sperm Cell 23 chromosomes Egg Cell The 23 chromosomes from sperm and egg combine during fertilization to make 46 in a human zygote!

2. What’s the difference between haploid and diploid cells? HAPLOID - n DIPLOID – 2n Two of each type of chromosome. One from mom and one from dad. Somatic cells(Blood, hair, skin) One of each type of chromosome Include Gametes like sperm and egg

3. Let’s Review Mitosis – Define: The process of ONE cell replicating its DNA and dividing into TWO identical Cells. Type of cells: Diploid Somatic Body Cells

Mitosis Chromosome Count 46 2n 46 46 46 2n Label the n and 2n cells

3. Meiosis Define: the process by which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. Reduction Division! Type of Cells: Gametes; sperm and egg

Meiosis Chromosome Count 23 Meiosis 2 2n 46 Meiosis 1 n 23 46 46 n 23 2n 23 n Label the n and 2n cells

Asexual vs. Sexual Reproduciton Asexual reproduction a single parent reproduces by itself. The offspring is an identical clone. Sexual Reproduction Two cells from different parents unite to produce the first cell of a genetically unique organism Mitosis! Meiosis!

Terms to know Sister Chromatids Homologous Chromosomes the two identical halves of a single replicated e chromosome and joined at the centromere. Chromosomes that code for the same thing One comes from the mom and one from the dad. Paternal Maternal eye color locus B = brown eyes b = blue eyes

*Remember that unorganized chromosomes are called Chromatin during interphase

MEIOSIS is all about creating VARIATION Every sperm and egg ever made is unique because of how meiosis works

6. How does meiosis create variation in sperm and egg? Homologous Chromosomes Cross Over before separating and exchange genetic variation. (Gene Shuffling)

This only happens during meiosis, not mitosis!

B. Chromosomes independently assort into gametes to increase genetic variation. (Blue eyes doesn’t always pair up with Freckles and maternal and paternal genes segregate randomly) B b sperm haploid (n) meiosis II Bb diploid (2n) meiosis I Ff F f This means all gametes will be different! Meiosis Video

7. What is the significance of meiosis to sexual reproduction; Meiosis reduces the number of chromosomes in each cell so that sexual reproduction is possible. YAY! Meiosis insures that every sperm and egg ever made will be a little bit different which means you won’t look exactly like your siblings. DOUBLE YAY! Species with more variation have a greater chance for survival! TRIPLE YAY!!!