Sec 4.3 Meiosis

1. Normal human body cells have 46 chromosomes, or two sets 1. Normal human body cells have 46 chromosomes, or two sets. One from mom and one from dad.

a. these cells are referred to as diploid or 2n b a. these cells are referred to as diploid or 2n b. how many chromosomes would the offspring have if these were the cells that created an offspring?

2. Gametes are cells that contain half the normal number of chromosomes.

a. these cells are referred to as haploid or n b a. these cells are referred to as haploid or n b. gametes are formed only in the reproductive organs. An egg is the female gamete and sperm is the male gamete.

c. fertilization occurs when the sperm unites with the egg to form an offspring with the normal number of chromosomes thus producing a diploid or 2n cell.

How are we doing? Answer the following questions on your output side of your notebook.

1. How many chromosomes does a normal human body cell have. 2 1. How many chromosomes does a normal human body cell have? 2. What does diploid mean or 2n? 3. How many chromosomes does a gamete have? 4. What is the male gamete? 5. What is the female gamete? 6. What is haploid or n?

3. Meiosis-sometimes referred to as reduction division because the cells undergo cell division twice so the cells will end up with only one chromosome from each pair

Meiosis I Interphase-the homologous (pair) of chromosomes copy themselves

Prophase I- Early Prophase I the chromosomes can become entangled and exchange corresponding sections of DNA, this is called “crossing over” Late Prophase I homologous chromosomes pair up and form a tetrad, nuclear membrane disappears, chromosomes condense into rod-like shape

Metaphase I-The chromosome pairs line up on the equator Metaphase I-The chromosome pairs line up on the equator. Anaphase I- The tetrad is separated and one chromosome pair goes to one pole and the other chromosome pair goes to the opposite pole.

Telophase I and Cytokinesis- The chromatids reach the pole, nuclear membrane reappears, cell membrane cuts through the cytoplasm to form two daughter cells

Prophase II- The homologous pair of chromatids are attached at the centromere Metaphase II- Chromatids line up on the equator

Anaphase II- Chromatids separate and are moved to opposite poles Telophase II and Cytokinesis- The cell membrane cuts through the cytoplasm of the two cells forming 4 cells that are haploid or n cells

males form 4 sperm cells here

females form 1 egg here, the other 3 are much smaller, called polar bodies and are dissolved back into the organism  

Final Check 1. What is the process that produces gametes. 2 Final Check 1. What is the process that produces gametes? 2. What is the purpose of meiosis? 3. In what phase does crossing over take place? 4. How many times does the cell divide in meiosis?

5. When does the DNA replicate. 6 5. When does the DNA replicate? 6. How many cells are produced for a female at the end of meiosis? 7. How many cells are produced for a male at the end of meiosis? 8. How is mitosis different from meiosis?