DO NOW: What is better: sexual or asexual reproduction?

Mitosis Vs. Meiosis There are two types of cell division that allow organisms to grow in size and in number. Cell division: the separation of one cell into two 2 types of cell division: ◦ Mitosis ◦ Meiosis

Mitosis Mitosis: makes body cells and helps the organism to grow in size by producing TWO identical diploid cells A type of asexual reproduction Produces Diploid cells: a cell with two copies of each chromosome (2N)

1. INTERPHASE 3 Different Phases: ◦ G1 Phase: Period when cell growth and development occur ◦ S Phase : DNA Replication / synthesis occurs ◦ G2 Phase: Organelles needed for cell division are made (Centrioles and Spindle Fibers)

2. PROPHASE The longest phase Chromosomes appear Centrioles move to opposite ends of the cell Chromosomes attach to the spindle Nucleolus and nuclear membrane breaks down

3. METAPHASE Shortest phase of mitosis Chromosomes line up at center of the cell

4. ANAPHASE Centromeres split Sister chromotids separate to form individual chromosomes Anaphase ends when the movement of chromosomes stops

5. TELOPHASE Chromosomes uncoil into chromatin Nuclear membrane reforms Spindle breaks apart

Meiosis Meiosis: makes sex cells and helps an organism to reproduce by producing different haploid cells Haploid: a cell with one copy of each chromosome (N) Male vs. Female: Meiosis produces 4 sperm cells in males and ONE egg cell in females

Why meiosis? Meiosis consists of two separate divisions, known as meiosis I and meiosis II. Meiosis I begins with one diploid (2n) cell. By the end of meiosis II, there are four haploid (n) cells. These haploid cells are called sex cells— gametes. Male gametes are called sperm. Female gametes are called eggs. When a sperm fertilizes an egg, the resulting zygote once again has the diploid number of chromosomes. This pattern of reproduction, involving the production and subsequent fusion of haploid sex cells, is called sexual reproduction

Comparing Mitosis and Meiosis

MitosisMeiosis Number of cell divisions?12 Exchange of genetic material?NoYes, crossing over! Number of functioning cells produce? 24 sperm in males 1 egg in females Offspring are..Identical to original Highly variable and diverse, contain half of the genetic information of the original Purpose?Growth or replacement of body cells Combine to form the zygote for reproduction

Pros and Cons MitosisMeiosis PositivesRepair old or damaged cells Make exact copies Varied offspring Species is more stable NegativesOrganisms are all the same so one disease can wipe out an entire population Requires 2 parents More time consuming