DNA can form many structures! The Many Forms of DNA DNA can form many structures!

I. Organization of Genetic Material Each human cell has about 6.5 feet of DNA →enough DNA in your whole body to go to the sun and back 500 times! → Question: How can you store all that DNA in your cells?

DNA can form many structures, and they all have different names! –––––– Chromatin DNA can form many structures, and they all have different names!

I. Organization of Genetic Material Chromatin: The form of DNA when it is NOT visible to the human eye Chromosome: The form of DNA when it is tightly coiled around histone proteins and is visible to the human eye.

I. Organization of Genetic Material What are genes?

I. Organization of Genetic Material A gene is a section of DNA that makes 1 protein. Alleles are different versions of the same gene. Gene for eye color proteins Gene for hair color proteins

I. Organization of Genetic Material Human Chromosome #20

E. How are chromosomes organized in the cell? I. Organization of Genetic Material E. How are chromosomes organized in the cell? Chromosomes come in pairs.

Chromosomes come in HOMOLOGOUS PAIRS I. Organization of Genetic Material Chromosomes come in HOMOLOGOUS PAIRS matching This is true for all organisms that have 2 parents… No matter what– a mouse, a fly, etc. Half of the chromosomes come from the FATHER. The other matching half comes from the MOTHER.

I. Organization of Genetic Material Gametes (sex cells: sperm or egg) Human gametes only have 23 chromosomes (no pairs! That’s half the DNA you have in all your other cells!

Why only HALF the chromosomes in gametes?? I. Organization of Genetic Material Why only HALF the chromosomes in gametes?? Think about it…

Imagine a human sperm and egg cell with full DNA coming together… I. Organization of Genetic Material Imagine a human sperm and egg cell with full DNA coming together… 46 Sperm (male sex cell) from Dad 46 Egg (female sex cell) from Mom 92 Baby’s first Body Cell (“Zygote”)

Now, imagine a sperm and egg cell with half DNA coming together… I. Organization of Genetic Material Now, imagine a sperm and egg cell with half DNA coming together… 23 Sperm (male gamete) from Dad 23 Egg (female gamete) from Mom 46 Baby’s first Body Cell (“Zygote”)

How do the sex cells get only half the number of chromosomes??? MEIOSIS!

DIPLOID (2n)= full set of chromosomes—1 from mom, one from dad I. Organization of Genetic Material Diploid v. Haploid: All organisms have a certain number of chromosomes in their SOMATIC (body) cells called the diploid number. DIPLOID (2n)= full set of chromosomes—1 from mom, one from dad Organism Diploid Number Human 46 (23 pairs) Corn 20 (10 pairs) Dog 78 (39 pairs) Chicken Crayfish 200 (100 pairs)

HAPLOID (1n)= half set of chromosomes I. Organization of Genetic Material Diploid v. Haploid: All organisms only have half the number of chromosomes in their GAMETES (sex cells) called the haploid chromosome number. HAPLOID (1n)= half set of chromosomes Organism Diploid Number Haploid Number Human 46 23 Corn 20 10 Dog 78 39 Chicken Crayfish 200 100

Quick Check! When DNA is tightly wrapped around proteins it is called a _____________. A section of DNA that makes one protein is called a ___________. Why do chromosomes come in homologous pairs? T/F: All cells have a full set of DNA and are called “diploid.” An elephant has 56 chromosomes. What is its haploid number (1n)?

Quick Check! When DNA is tightly wrapped around proteins it is called a chromosome. A section of DNA that makes one protein is called a gene. Why do chromosomes come in homologous pairs? T/F: All cells have a full set of DNA and are called “diploid.” FALSE An elephant has 56 chromosomes. What is its haploid number (1n)? 28

How does a body make gametes? Say “My-OH-sis” Meiosis: How does a body make gametes?

So…do all cells in the body have the same number of chromosomes? Review: Pair and Share How is DNA stored in a cell? What is the difference between somatic (body) cells and gametes (sex) cells? So…do all cells in the body have the same number of chromosomes?

SOMATIC CELLS (body cells) are DIPLOID (2n) = TWO full sets of chromosomes Organism Diploid Number Human 46 (23 pairs) Corn 20 (10 pairs) Dog 78 (39 pairs) Chicken Crayfish 200 (100 pairs) Adder’s Tongue 1260 (630 pairs) Do you know where they get each set?

GAMETES (sex cells) are HAPLOID (1n) = ONE full set of chromosomes Organism Diploid Number Haploid Number Human 46 23 Corn 20 10 Dog 78 39 Chicken Crayfish 200 100 Adder’s 1260 630

Gametes (sex cells) need to be haploid! II. Meiosis Overview Gametes (sex cells) need to be haploid! 23 23 Male Gamete (sperm) Female Gamete (egg) 46 ZYGOTE

A. If your body needs a new somatic (body) cell… II. Meiosis Overview A. If your body needs a new somatic (body) cell… How does that cell get made? (Hint: think of the cell cycle) DNA Replication, then MITOSIS (one cell splits into two)

If your body needs a new gamete(sex cell)… II. Meiosis Overview If your body needs a new gamete(sex cell)… How does that cell get made? DNA replication, then MEIOSIS (one cell splits into four)

Compare and Contrast: Mitosis versus Meiosis II. Meiosis Overview Compare and Contrast: Mitosis versus Meiosis

III. Stages of Meiosis 0. INTERPHASE (Pre-Meiosis) Cell does DNA replication *NOTE* Meiosis ONLY happens in the OVARIES & TESTES (sex organs) Homologous pair Another homologous pair

III. Stages of Meiosis A closer look… INTERPHASE “sister chromatids” Still homologous pairs, there’s just a copy of each now! Q: What is similar about these sister chromatids?

III. Stages of Meiosis 1. Prophase 1 centrioles Chromosomes condense and become visible Homologous chromosomes come together and Pair up Crossing over occurs *** Nuclear membrane disappears Spindle fibers form from centrioles and will attach to sister chromatids at their centromeres !

III. Stages of Meiosis 2. Metaphase 1 Spindles move the homologous pairs toward the Middle

III. Stages of Meiosis 3. Anaphase 1 Homologous pairs get pulled Apart to opposite sides with the shortening of the spindle fibers

4. Telophase 1 (and Cytokinesis) III. Stages of Meiosis 4. Telophase 1 (and Cytokinesis) The cell splits into Two cells Other things going on: Nuclear membrane starts to form again Spindles disappear Period 5 – No cool down and no PMAT

WOW! We just made 1 cell split into 2… How will you remember all those phases? Prophase Metaphase Anaphase Telophase How will we make 4 cells??? Paco Made Estoy haciendo un taco. Paco A Taco

To make gametes, the cells in our sex organs repeat P-M-A-T! Going through P-M-A-T two times will complete the meiosis process. Let’s continue…

III. Stages of Meiosis 5. Prophase 2 Chromosomes condense and become visible Both cells Prepare to split again No crossing over Nuclear membrane disappears again Spindle fibers form again and attach to centromeres

III. Stages of Meiosis 6. Metaphase 2 Sister chromatids line up in the Middle

III. Stages of Meiosis 7. Anaphase 2 Sister chromatids get pulled Apart to opposite ends as spindle fibers shorten

8. Telophase 2 (and cytokinesis) III. Stages of Meiosis 8. Telophase 2 (and cytokinesis) Each cell splits into Two cells-- totaling 4 haploid cells Other things going on: Nuclear membrane appears again Spindles disappear

Result: Now we have 4 HAPLOID cells!

QUICK CHECK! How does the original parent cell compare to the daughter cells in: Chromosome number? Genetic information in chromosomes?

The BIG FINISH Identify 3 differences between MITOSIS and MEIOSIS.

MITOSIS (making SOMATIC cells) MEIOSIS (making GAMETES) The BIG PICTURE Work with a partner to fill in the chart below… MITOSIS (making SOMATIC cells) MEIOSIS (making GAMETES) Number of cells at start 1 How many times does DNA replication happen? How many times does the cell divide its nucleus? How many cells at the end? Are the cells DIPLOID or HAPLOID?

MITOSIS (making SOMATIC cells) MEIOSIS (making GAMETES) The BIG PICTURE Work with a partner to fill in the chart below… MITOSIS (making SOMATIC cells) MEIOSIS (making GAMETES) Number of cells at start 1 How many times does DNA replication happen? How many times does the cell divide its nucleus? 2 How many cells at the end? 4 Are the cells DIPLOID or HAPLOID? DIPLOID HAPLOID