Chapter 4: Reproduction of Organisms Life Science 7th grade

Inquiry Do you think ALL living things have two parents? What might happen if the penguins (on the chapter cover photo) did not reproduce? Why do you think living things reproduce?

Bell work Ch4. L1 Sexual reproduction: reproduction in which the genetic materials from two different cells combine, producing an offspring. Egg: female sex cell that forms in the ovary. Sperm: male sex cell that forms in the testis. Fertilization: the process during which an egg cell and a sperm cell join together to form a new cell. Zygote: The new cell that is formed as a result of fertilization. Diploid cell: Cells that have pairs of chromosomes Homologous chromosomes: pairs of chromosomes that have genes for the same trait arranged in the same order Haploid cell: Cells that only have one chromosome from each pair Meiosis: The process by which one diploid cell divides to make four haploid cells

Launch Lab (work in pairs) Each pair gets one “male parent” and one “female parent bag” Without looking in the bag, select three beads from each bag. Record bead colors from each bag The six beads you pulled represent one offspring (x4) Put beads back in respective bags after each offspring Offspring #1 Offspring #2 Offspring #3 Offspring #4 Male bag Female bag 1- How are the offspring similar? How are they different? 2- Why were there differences between offspring? Are differences beneficial? Why or why not?

What is sexual reproduction? Reproduction in which the genetic materials from two different cells combine, producing an offspring. Those cells are called sex cells Sex cells form in reproductive organs What are sex cells in humans and where do they form?

Sex cells Egg Sperm Female sex cell Forms in ovary Male sex cell Forms in testis

Fertilization An egg cell and a sperm cell join together This forms a new cell Zygote= new cell that forms from fertilization Develops into an organism What process is responsible for the development of a zygote into an organism?

Diploid cells Cells that have pairs of chromosomes Video Similar chromosomes occur in pairs This happens in body cells Diploid cells are produced via mitosis Video

Chromosomes Homologous chromosomes: pairs of chromosomes that have genes for the same trait arranged in the same order One from mom, one from dad make up a pair *****NOT IDENTICAL= DIFFERENT FROM SISTER CHROMATIDS.****** Video DO YOU THINK A MORE COMPLICATED ORGANISM HAS MORE CHROMOSOMES THAN A SIMPLER ORGANISM?

How many chromosomes? Human body cells have 23 pairs of chromosomes= 46 total chromosomes Number of chromosomes does NOT correlate with how complicated an organism is Dog has 78, Fern has 1,260 chromosomes Human on top, dog on bototm.

Haploid cells Cells that only have one chromosome from each pair (in humans have 23 total, not 46 total) Sex cells are haploid Haploid cells are produced via meiosis ONE STEP UP: WHY do you think sex cells are haploid?

Meiosis overview Many similarities to mitosis Mitosis+cytokinesis= one division of nucleus + one division of cytoplasm End result= Two diploid cells Meiosis= TWO divisions of nucleus and TWO divisions of cytoplasm End result= FOUR haploid cells Happens in two phases- meiosis I and meiosis II Video

Meiosis - phases Interphase- EXACTLY THE SAME AS IN MITOSIS. Period of growth and replication. Chromosomes are duplicated and each duplicated chromosome has two sister chromatids joined at the centromere. This only happens once

Meiosis I - phases Prophase I: chromosomes condense, homologous chromosomes form pairs. Nuclear envelope breaks apart, nucleolus disappears.

Meiosis I - phases Metaphase I: Homologous chromosomes line up along the middle of the cell. Spindle fiber attaches to centromere.

Meiosis I - phases Anaphase I: Chromosomes pairs (homologous chromosomes) are pulled apart. SISTER CHROMATIDS STAY TOGETHER.

Meiosis I - phases Telophase I: Nuclear membrane reappears around PAIRS of chromosomes, nucleolus reappears. Cytoplasm divides through cytokinesis. Two daughter cells form.

Meiosis II - phases NO SECOND INTERPHASE. Daughter cells from meiosis I immediately undergo meiosis II Prophase II: Because no replication, chromosomes stayed as thick sister chromatids Nuclear envelope breaks down Nucleolus disappears.

Meiosis II - phases Metaphase II: Sister chromatids line up along the middle of the cell Spindle attaches to centromere.

Meiosis II - phases Anaphase II: Sister chromatids pulled apart and move toward opposite ends of the cell

Meiosis II - phases Telophase II: Result= four haploid cells. Nuclear membrane forms around chromosomes cytoplasm divides via cytokinesis. Result= four haploid cells.

Meiosis Video

Meiosis summary Interphase Prophase I Metaphase I Anaphase I Cell growth and replication. Sister chromatids attached at centromere. Prophase I Homologous chromosomes form pairs, nuclear membrane breaks apart, nucleolus disappears Metaphase I Homologous chromosomes line up in center of cell, spindle fiber attaches to each chromosome Anaphase I Homologous chromosomes pulled apart towards opposite ends of the cell. SISTER CHROMATIDS stay together. Telophase I Nuclear membrane forms around sister chromatids, cytokinesis divides cytoplasm. Two daughter cells formed. Prophase II Nuclear membrane breaks apart, nucleolus disappears. Metaphase II Sister chromatids line up along metaphase plate, spindle fiber attaches to centromere. Anaphase II Sister chromatids pulled apart towards opposite ends of cell. Telophase II Nuclear envelope reappears around individual chromosomes, nucleolus reappears. Cytokinesis divides cell. End Result: FOUR haploid cells

Why is meiosis important? Maintains diploid cells When haploid cells join (via fertilization) they make a diploid cell= zygote. Zygote then divides via mitosis to make the organism Creates haploid cells Maintains correct number of chromosomes in sex cells so when they join, they form a zygote with the correct number of chromosomes

Mitosis vs Meiosis (table p.122) Characteristic Meiosis Mitosis and Cell division Number of chromosomes in parent cell Diploid Type of parent cell Reproductive Body Number of divisions of nucleus 2 1 Number of daughter cells produced 4 Chromosome number in daughter cells Haploid Function Forms sperm and egg cell Growth, cell repair, some kinds of reproduction

Advantages of sexual reproduction Genetic variation Inherit different genes from parents compared to siblings Occurs in all organisms that reproduce sexually Includes plants Selective breeding Choose the traits you like (breed individuals with those traits) and over time those can become dominant Video

Disadvantages of sexual reproduction Takes time and energy Search for mate can be problematic Expose to predators, disease or harsh environments Limitations Gestational period (pregnancy) Can’t get pregnant while already pregnant, have to wait for one to finish before can start another one ONE STEP UP: Can you think of a way some organisms overcome the gestational limitation?

HOMEWORK Ch4 L.1 Vocabulary words on flash cards Memorize for quiz Lesson review questions p.126 #1-10 Outline lesson 1 Quiz lesson 1

Meiosis lab p.138 Let’s recreate mitosis and meiosis using pool noodles 8 volunteers to be chromosomes Each person gets one 8 volunteers to be nuclear envelope Surrounds chromosomes 8 volunteers to be spindle 8 volunteers to be narrators/puppeteers

Bell Work Ch4 L.2 Asexual reproduction: the process by which one parent organism produces offspring WITHOUT meiosis and fertilization Fission: cell division in prokaryotes that forms two genetically identical cells Budding: the process by which a new organism grows by mitosis and cell division on the body of its parent. Regeneration: occurs when an offspring grows from a piece of its parent Vegetative reproduction: a form of asexual reproduction in which offspring grow form a part of a parent plant Cloning: a type of asexual reproduction performed in a laboratory that produces identical individuals from a cell or from a cluster of cells taken from a multicellular organism

Yeast launch lab p.129 I warmed water to 34˚C (93˚F) I added 5g yeast and 5g sugar What does the mixture look like initially? After 5 minutes? Drop of solution onto slide (cover with cover slip) Draw what you see under microscope. Evidence of reproduction? TURN THIS IN

What is asexual reproduction? One parent organism produces offspring WITHOUT meiosis and fertilization. Inherit all DNA from one parent What are some advantages/disadvantages of reproducing this way? Mold: a type of fungus that can reproduce sexually OR asexually. (fuzzy stuff on old food) Bacteria, protists, plants and some animals can reproduce asexually ONE STEP UP: How do parent/daughter cells compare to each other in asexual reproduction?

Types of asexual reproduction Fission: cell division in prokaryotes that forms two genetically identical cells. Prokaryote’s DNA is copied Each copy attaches to cell membrane Cell elongates, pulling copies of DNA apart Cell membrane pinches inward along middle of the cell Cell splits and forms two new identical offspring Example: E.coli

Types of asexual reproduction Mitotic cell division: used by unicellular eukaryotes Organism produces two offspring through mitosis and cell division Example: amoeba

Types of asexual reproduction Budding: a new organism grows by mitosis and cell division on the body of its parent. Bud is genetically identical to parent When bud gets big enough, it can break off from parent Example: hydra (multicellular organism), yeast (unicellular organism). Genus of small, simple, fresh-water animals that possess radial symmetry

Types of asexual reproduction Animal regeneration: occurs when an offspring grows from a piece of its parent. (varies greatly among animals) Producing new organisms: each new organism is identical to starting organism Example: planarian (can cut in half and each half makes a new organism), sea star (can cut an arm and if it contains part of central disk and conditions are right, that arm will make a whole new star)

Types of asexual reproduction Animal regeneration cont’d Producing new parts: regeneration Common in animals. Humans can regenerate skin or liver, some animals can regenerate limbs. THIS IS NOT CONSIDERED ASEXUAL REPRODUCTION BECAUSE IT DOES NOT PRODUCE A NEW ORGANISM

Types of asexual reproduction Vegetative reproduction: a form of asexual reproduction in which offspring grow form a part of a parent plant. Parent plant can grow long stems called stolons If a stolon touches the ground, it forms roots. Once roots are down, a new plant can grow. If stolon is broken from parent plant, the new plant can survive on its own. Example: strawberries, raspberries and potatoes.

Types of asexual reproduction Cloning: a type of asexual reproduction performed in a laboratory that produces identical individuals from a cell or from a cluster of cells taken from a multicellular organism.

Types of asexual reproduction Plant cloning: do via tissue culture. Use cells from meristem to grow new plants in lab Animal cloning (Example: sheep) Take cell from sheep 1, take unfertilized egg from sheep 2 Remove DNA from unfertilized egg (it’s an empty egg now) Fuse cell from sheep 1 with empty egg from sheep 2 Cell develops into embryo in laboratory Implant embryo into sheep 2 Sheep 2 gives birth to clone of sheep 1 Video

Advantages of asexual reproduction Don’t need a mate Rapidly produce a large number of offspring

Disadvantages of asexual reproduction Genetically identical to parent= little variation within a population Variation can give better chance of survival Mutations Harmful mutations will be passed on to all offspring

HOMEWORK Ch4 L.2 Vocabulary wordsß on flash cards Memorize for quiz Lesson review questions p.137 #1-9 Outline lesson 2 Quiz lesson 2 OPTIONAL: Extra credit (due on test day) p.141-145 (all) You MUST write the entire question and answer down for credit. Only answers will NOT be accepted.