Life Science
7th grade

• 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?

• 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

• 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?

• 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?

• Egg
– Female sex cell
– Forms in ovary
• Sperm
– Male sex cell
– Forms in testis

• 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?

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

• 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?

• 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

• 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?

• 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

• 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

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

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

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

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

• 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.

• Metaphase II:
– Sister chromatids line up along the middle of the cell
– Spindle attaches to centromere.

• Anaphase II:
Sister chromatids pulled apart and move toward opposite ends of the cell

• Telophase II:
– Nuclear membrane forms around chromosomes
– cytoplasm divides via cytokinesis.
• Result= four haploid cells.

• Video

Interphase 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

• 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

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

• 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?

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

• 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

• 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

• 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

• 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?

• Fission: cell division in prokaryotes that forms two genetically identical cells.
1.
Prokaryote’s DNA is copied
2.
Each copy attaches to cell membrane
3.
Cell elongates, pulling copies of DNA apart
4.
Cell membrane pinches inward along middle of the cell
5.
Cell splits and forms two new identical offspring
• Example: E.coli

• Mitotic cell division: used by unicellular eukaryotes
– Organism produces two offspring through mitosis and cell division
• Example: amoeba

• 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).

• 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)

• 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

• Vegetative reproduction: a form of asexual reproduction in which offspring grow form a part of a parent plant.
1. Parent plant can grow long stems called stolons
2.
If a stolon touches the ground, it forms roots.
3. Once roots are down, a new plant can grow.
4. If stolon is broken from parent plant, the new plant can survive on its own.
– Example: strawberries, raspberries and potatoes.

• 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.

• 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

• Don’t need a mate
• Rapidly produce a large number of offspring

• 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

• 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.